PostgreSQL Benchmarks

[Christopher Kings-Lynne]

Hrm. I just saw that the PHP ADODB guy just published a bunch of database
benchmarks. It's fairly evident to me that benchmarking PostgreSQL on
Win32 isn't really fair:

http://php.weblogs.com/oracle_mysql_performance

*sigh*

Chris



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[Mario Weilguni]

Post by Christopher Kings-Lynne
Hrm. I just saw that the PHP ADODB guy just published a bunch of database
benchmarks. It's fairly evident to me that benchmarking PostgreSQL on
http://php.weblogs.com/oracle_mysql_performance

And why is the highly advocated transaction capable MySQL 4 not tested?
That's the problem, for every performance test they choose ISAM tables, and
when transactions are mentioned it's said "MySQL has transactions". But why
no benchmarks?

Regards,
Mario Weilguni

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[Greg Copeland]

Post by Mario Weilguni

Post by Christopher Kings-Lynne
Hrm. I just saw that the PHP ADODB guy just published a bunch of database
benchmarks. It's fairly evident to me that benchmarking PostgreSQL on
http://php.weblogs.com/oracle_mysql_performance

And why is the highly advocated transaction capable MySQL 4 not tested?
That's the problem, for every performance test they choose ISAM tables, and
when transactions are mentioned it's said "MySQL has transactions". But why
no benchmarks?

Insert Statement

Not using bind variables (MySQL and Oracle):
$DB->BeginTrans();



Using bind variables:
$DB->BeginTrans();


PL/SQL Insert Benchmark
Appears to not initiate a transaction. I'm assuming this is because
it's implicitly within a transaction? Oddly enough, I am seeing
explicit commits here.

It appears that the benchmarks are attempting to use transactions,
however, I have no idea if MySQL's HEAP supports them. For all I know,
transactions are being silently ignored.


Regards,

[Shridhar Daithankar]

Post by Mario Weilguni

Post by Christopher Kings-Lynne
Hrm. I just saw that the PHP ADODB guy just published a bunch of database
benchmarks. It's fairly evident to me that benchmarking PostgreSQL on
http://php.weblogs.com/oracle_mysql_performance

And why is the highly advocated transaction capable MySQL 4 not tested?
That's the problem, for every performance test they choose ISAM tables, and
when transactions are mentioned it's said "MySQL has transactions". But why
no benchmarks?

I did benchmark mysql/postgresql/oracle sometime back. Mysql with transaction
is 90% as fast as postgresql. But it dies down with increased number of users
no matter how much resources you throw at it.

Oracle is 130% of postgresql. This was postgresql 7.2.x series so things have
changed for sure, but you got the idea, right?

Shridhar

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[ow]

There's "The Open Source Database Benchmark",
http://osdb.sourceforge.net/.

Anyone tried to use it?





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[Greg Copeland]

Post by Christopher Kings-Lynne
Hrm. I just saw that the PHP ADODB guy just published a bunch of database
benchmarks. It's fairly evident to me that benchmarking PostgreSQL on
http://php.weblogs.com/oracle_mysql_performance
*sigh*

How much of the performance difference is from the RDBMS, from the
middleware, and from the quality of implementation in the middleware.

While I'm not surprised that the the cygwin version of PostgreSQL is
slow, those results don't tell me anything about the quality of the
middleware interface between PHP and PostgreSQL. Does anyone know if we
can rule out some of the performance loss by pinning it to bad
middleware implementation for PostgreSQL?


Regards,

[Merlin Moncure]

I've tested all the win32 versions of postgres I can get my hands on
(cygwin and not), and my general feeling is that they have problems with
insert performance with fsync() turned on, probably the fault of the os.
Select performance is not so much affected.

This is easily solved with transactions and other such things. Also
Postgres benefits from pl just like oracle.

May I make a suggestion that maybe it is time to start thinking about
tuning the default config file, IMHO its just a little bit too
conservative, and its hurting you in benchmarks being run by idiots, but
its still bad publicity. Any real database admin would know his test
are synthetic and not meaningful without having to look at the #s.

This is irritating me so much that I am going to put together a
benchmark of my own, a real world one, on (publicly available) real
world data. Mysql is a real dog in a lot of situations. The FCC
publishes a database of wireless transmitters that has tables with 10
million records in it. I'll pump that into pg, run some benchmarks,
real world queries, and we'll see who the faster database *really* is.
This is just a publicity issue, that's all. Its still annoying though.

I'll even run an open challenge to database admin to beat query
performance of postgres in such datasets, complex multi table joins,
etc. I'll even throw out the whole table locking issue and analyze
single user performance.

Merlin



_____________
How much of the performance difference is from the RDBMS, from the
middleware, and from the quality of implementation in the middleware.

While I'm not surprised that the the cygwin version of PostgreSQL is
slow, those results don't tell me anything about the quality of the
middleware interface between PHP and PostgreSQL. Does anyone know if we
can rule out some of the performance loss by pinning it to bad
middleware implementation for PostgreSQL?


Regards,
--
Greg Copeland <***@copelandconsulting.net>
Copeland Computer Consulting




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[Tom Lane]

Post by Merlin Moncure
May I make a suggestion that maybe it is time to start thinking about
tuning the default config file, IMHO its just a little bit too
conservative,

It's a lot too conservative. I've been thinking for awhile that we
should adjust the defaults.

The original motivation for setting shared_buffers = 64 was so that
Postgres would start out-of-the-box on machines where SHMMAX is 1 meg
(64 buffers = 1/2 meg, leaving 1/2 meg for our other shared data
structures). At one time SHMMAX=1M was a pretty common stock kernel
setting. But our other data structures blew past the 1/2 meg mark
some time ago; at default settings the shmem request is now close to
1.5 meg. So people with SHMMAX=1M have already got to twiddle their
postgresql.conf settings, or preferably learn how to increase SHMMAX.
That means there is *no* defensible reason anymore for defaulting to
64 buffers.

We could retarget to try to stay under SHMMAX=4M, which I think is
the next boundary that's significant in terms of real-world platforms
(isn't that the default SHMMAX on some BSDen?). That would allow us
350 or so shared_buffers, which is better, but still not really a
serious choice for production work.

What I would really like to do is set the default shared_buffers to
1000. That would be 8 meg worth of shared buffer space. Coupled with
more-realistic settings for FSM size, we'd probably be talking a shared
memory request approaching 16 meg. This is not enough RAM to bother
any modern machine from a performance standpoint, but there are probably
quite a few platforms out there that would need an increase in their
stock SHMMAX kernel setting before they'd take it.

So what this comes down to is making it harder for people to get
Postgres running for the first time, versus making it more likely that
they'll see decent performance when they do get it running.

It's worth noting that increasing SHMMAX is not nearly as painful as
it was back when these decisions were taken. Most people have moved
to platforms where it doesn't even take a kernel rebuild, and we've
acquired documentation that tells how to do it on all(?) our supported
platforms. So I think it might be okay to expect people to do it.

The alternative approach is to leave the settings where they are, and
to try to put more emphasis in the documentation on the fact that the
factory-default settings produce a toy configuration that you *must*
adjust upward for decent performance. But we've not had a lot of
success spreading that word, I think. With SHMMMAX too small, you
do at least get a pretty specific error message telling you so.

Comments?

regards, tom lane

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[Greg Copeland]

Post by Tom Lane

Post by Merlin Moncure
May I make a suggestion that maybe it is time to start thinking about
tuning the default config file, IMHO its just a little bit too
conservative,

It's a lot too conservative. I've been thinking for awhile that we
should adjust the defaults.
The original motivation for setting shared_buffers = 64 was so that
Postgres would start out-of-the-box on machines where SHMMAX is 1 meg
(64 buffers = 1/2 meg, leaving 1/2 meg for our other shared data
structures). At one time SHMMAX=1M was a pretty common stock kernel
setting. But our other data structures blew past the 1/2 meg mark
some time ago; at default settings the shmem request is now close to
1.5 meg. So people with SHMMAX=1M have already got to twiddle their
postgresql.conf settings, or preferably learn how to increase SHMMAX.
That means there is *no* defensible reason anymore for defaulting to
64 buffers.
We could retarget to try to stay under SHMMAX=4M, which I think is
the next boundary that's significant in terms of real-world platforms
(isn't that the default SHMMAX on some BSDen?). That would allow us
350 or so shared_buffers, which is better, but still not really a
serious choice for production work.
What I would really like to do is set the default shared_buffers to
1000. That would be 8 meg worth of shared buffer space. Coupled with
more-realistic settings for FSM size, we'd probably be talking a shared
memory request approaching 16 meg. This is not enough RAM to bother
any modern machine from a performance standpoint, but there are probably
quite a few platforms out there that would need an increase in their
stock SHMMAX kernel setting before they'd take it.
So what this comes down to is making it harder for people to get
Postgres running for the first time, versus making it more likely that
they'll see decent performance when they do get it running.
It's worth noting that increasing SHMMAX is not nearly as painful as
it was back when these decisions were taken. Most people have moved
to platforms where it doesn't even take a kernel rebuild, and we've
acquired documentation that tells how to do it on all(?) our supported
platforms. So I think it might be okay to expect people to do it.
The alternative approach is to leave the settings where they are, and
to try to put more emphasis in the documentation on the fact that the
factory-default settings produce a toy configuration that you *must*
adjust upward for decent performance. But we've not had a lot of
success spreading that word, I think. With SHMMMAX too small, you
do at least get a pretty specific error message telling you so.
Comments?

I'd personally rather have people stumble trying to get PostgreSQL
running, up front, rather than allowing the lowest common denominator
more easily run PostgreSQL only to be disappointed with it and move on.

After it's all said and done, I would rather someone simply say, "it's
beyond my skill set", and attempt to get help or walk away. That seems
better than them being able to run it and say, "it's a dog", spreading
word-of-mouth as such after they left PostgreSQL behind. Worse yet,
those that do walk away and claim it performs horribly are probably
doing more harm to the PostgreSQL community than expecting someone to be
able to install software ever can.

Nutshell:
"Easy to install but is horribly slow."

or

"Took a couple of minutes to configure and it rocks!"



Seems fairly cut-n-dry to me. ;)


Regards,

[Jason Hihn]

Post by Greg Copeland
"Easy to install but is horribly slow."
or
"Took a couple of minutes to configure and it rocks!"

Since when is it easy to install on win32?
The easiest way I know of is through Cygwin, then you have to worry about
installing the IPC service (an getting the right version too!) I've
installed versions 6.1 to 7.1, but I almost gave up on the windows install.
At least in 6.x you had very comprehensive installation guide with a TOC.

Versus the competition which are you going to choose if you're a wanna-be
DBA? The one with all he hoops to jump through, or the one that comes with a
setup.exe?

Now I actually am in support of making it more aggressive, but it should
wait until we too have a setup.exe for the native windows port. (Changing it
on *n*x platforms is of little benefit because most benchmarks seem to run
it on w32 anyway :-( )

Just my $.02. I reserve the right to be wrong.
-J


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[mlw]

Post by Greg Copeland
I'd personally rather have people stumble trying to get PostgreSQL
running, up front, rather than allowing the lowest common denominator
more easily run PostgreSQL only to be disappointed with it and move on.
After it's all said and done, I would rather someone simply say, "it's
beyond my skill set", and attempt to get help or walk away. That seems
better than them being able to run it and say, "it's a dog", spreading
word-of-mouth as such after they left PostgreSQL behind. Worse yet,
those that do walk away and claim it performs horribly are probably
doing more harm to the PostgreSQL community than expecting someone to be
able to install software ever can.

<RANT>

And that my friends is why PostgreSQL is still relatively obscure.

This attitude sucks. If you want a product to be used, you must put the
effort into making it usable.

It is a no-brainer to make the default configuration file suitable for
the majority of users. It is lunacy to create a default configuration
which provides poor performance for over 90% of the users, but which
allows the lowest common denominator to work.

A product must not perform poorly out of the box, period. A good product
manager would choose one of two possible configurations, (a) a high
speed fairly optimized system from the get-go, or (b) it does not run
unless you create the configuration file. Option (c) out of the box it
works like crap, is not an option.

This is why open source gets such a bad reputation. Outright contempt
for the user who may not know the product as well as those developing
it. This attitude really sucks and it turns people off. We want people
to use PostgreSQL, to do that we must make PostgreSQL usable. Usability
IS important.
</RANT>



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[Greg Copeland]

Post by mlw

Post by Greg Copeland
I'd personally rather have people stumble trying to get PostgreSQL
running, up front, rather than allowing the lowest common denominator
more easily run PostgreSQL only to be disappointed with it and move on.
After it's all said and done, I would rather someone simply say, "it's
beyond my skill set", and attempt to get help or walk away. That seems
better than them being able to run it and say, "it's a dog", spreading
word-of-mouth as such after they left PostgreSQL behind. Worse yet,
those that do walk away and claim it performs horribly are probably
doing more harm to the PostgreSQL community than expecting someone to be
able to install software ever can.

<RANT>
And that my friends is why PostgreSQL is still relatively obscure.
This attitude sucks. If you want a product to be used, you must put the
effort into making it usable.

Ah..okay....

Post by mlw
It is a no-brainer to make the default configuration file suitable for
the majority of users. It is lunacy to create a default configuration
which provides poor performance for over 90% of the users, but which
allows the lowest common denominator to work.

I think you read something into my email which I did not imply. I'm
certainly not advocating a default configuration file assuming 512M of
share memory or some such insane value.

Basically, you're arguing that they should keep doing exactly what they
are doing. It's currently known to be causing problems and propagating
the misconception that PostgreSQL is unable to perform under any
circumstance. I'm arguing that who cares if 5% of the potential user
base has to learn to properly install software. Either they'll read and
learn, ask for assistance, or walk away. All of which are better than
Jonny-come-lately offering up a meaningless benchmark which others are
happy to eat with rather large spoons.

Post by mlw
A product must not perform poorly out of the box, period. A good product
manager would choose one of two possible configurations, (a) a high
speed fairly optimized system from the get-go, or (b) it does not run
unless you create the configuration file. Option (c) out of the box it
works like crap, is not an option.

That's the problem. Option (c) is what we currently have. I'm amazed
that you even have a problem with option (a), as that's what I'm
suggesting. The problem is, potentially for some minority of users, it
may not run out of the box. As such, I'm more than happy with this
situation than 90% of the user base being stuck with a crappy default
configuration.

Oddly enough, your option (b) is even worse than what you are ranting at
me about. Go figure.

Post by mlw
This is why open source gets such a bad reputation. Outright contempt
for the user who may not know the product as well as those developing
it. This attitude really sucks and it turns people off. We want people
to use PostgreSQL, to do that we must make PostgreSQL usable. Usability
IS important.
</RANT>

There is no contempt here. Clearly you've read your own bias into this
thread. If you go back and re-read my posting, I think it's VERY clear
that it's entirely about usability.


Regards,

[mlw]

Apology

After Mark calms down and, in fact, sees that Greg was saying the right
thing after all, chagrin is the only word.

I'm sorry.

Post by Greg Copeland

Post by mlw

Post by Greg Copeland
I'd personally rather have people stumble trying to get PostgreSQL
running, up front, rather than allowing the lowest common denominator
more easily run PostgreSQL only to be disappointed with it and move on.
After it's all said and done, I would rather someone simply say, "it's
beyond my skill set", and attempt to get help or walk away. That seems
better than them being able to run it and say, "it's a dog", spreading
word-of-mouth as such after they left PostgreSQL behind. Worse yet,
those that do walk away and claim it performs horribly are probably
doing more harm to the PostgreSQL community than expecting someone to be
able to install software ever can.

<RANT>
And that my friends is why PostgreSQL is still relatively obscure.
This attitude sucks. If you want a product to be used, you must put the
effort into making it usable.

Ah..okay....

Post by mlw
It is a no-brainer to make the default configuration file suitable for
the majority of users. It is lunacy to create a default configuration
which provides poor performance for over 90% of the users, but which
allows the lowest common denominator to work.

I think you read something into my email which I did not imply. I'm
certainly not advocating a default configuration file assuming 512M of
share memory or some such insane value.
Basically, you're arguing that they should keep doing exactly what they
are doing. It's currently known to be causing problems and propagating
the misconception that PostgreSQL is unable to perform under any
circumstance. I'm arguing that who cares if 5% of the potential user
base has to learn to properly install software. Either they'll read and
learn, ask for assistance, or walk away. All of which are better than
Jonny-come-lately offering up a meaningless benchmark which others are
happy to eat with rather large spoons.

Post by mlw
A product must not perform poorly out of the box, period. A good product
manager would choose one of two possible configurations, (a) a high
speed fairly optimized system from the get-go, or (b) it does not run
unless you create the configuration file. Option (c) out of the box it
works like crap, is not an option.

That's the problem. Option (c) is what we currently have. I'm amazed
that you even have a problem with option (a), as that's what I'm
suggesting. The problem is, potentially for some minority of users, it
may not run out of the box. As such, I'm more than happy with this
situation than 90% of the user base being stuck with a crappy default
configuration.
Oddly enough, your option (b) is even worse than what you are ranting at
me about. Go figure.

Post by mlw
This is why open source gets such a bad reputation. Outright contempt
for the user who may not know the product as well as those developing
it. This attitude really sucks and it turns people off. We want people
to use PostgreSQL, to do that we must make PostgreSQL usable. Usability
IS important.
</RANT>

There is no contempt here. Clearly you've read your own bias into this
thread. If you go back and re-read my posting, I think it's VERY clear
that it's entirely about usability.
Regards,

[scott.marlowe]

My other pet peeve is the default max connections setting. This should be
higher if possible, but of course, there's always the possibility of
running out of file descriptors.

Apache has a default max children of 150, and if using PHP or another
language that runs as an apache module, it is quite possible to use up all
the pgsql backend slots before using up all the apache child slots.

Is setting the max connections to something like 200 reasonable, or likely
to cause too many problems?


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[Tom Lane]

Post by scott.marlowe
Is setting the max connections to something like 200 reasonable, or likely
to cause too many problems?

That would likely run into number-of-semaphores limitations (SEMMNI,
SEMMNS). We do not seem to have as good documentation about changing
that as we do about changing the SHMMAX setting, so I'm not sure I want
to buy into the "it's okay to expect people to fix this before they can
start Postgres the first time" argument here.

Also, max-connections doesn't silently skew your testing: if you need
to raise it, you *will* know it.

regards, tom lane

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[Greg Copeland]

Post by Tom Lane

Post by scott.marlowe
Is setting the max connections to something like 200 reasonable, or likely
to cause too many problems?

That would likely run into number-of-semaphores limitations (SEMMNI,
SEMMNS). We do not seem to have as good documentation about changing
that as we do about changing the SHMMAX setting, so I'm not sure I want
to buy into the "it's okay to expect people to fix this before they can
start Postgres the first time" argument here.
Also, max-connections doesn't silently skew your testing: if you need
to raise it, you *will* know it.

Besides, I'm not sure that it makes sense to let other product needs
dictate the default configurations for this one. It would be one thing
if the vast majority of people only used PostgreSQL with Apache. I know
I'm using it in environments in which no way relate to the web. I'm
thinking I'm not alone.


Regards,

[scott.marlowe]

Post by Greg Copeland

Post by Tom Lane

Post by scott.marlowe
Is setting the max connections to something like 200 reasonable, or likely
to cause too many problems?

That would likely run into number-of-semaphores limitations (SEMMNI,
SEMMNS). We do not seem to have as good documentation about changing
that as we do about changing the SHMMAX setting, so I'm not sure I want
to buy into the "it's okay to expect people to fix this before they can
start Postgres the first time" argument here.
Also, max-connections doesn't silently skew your testing: if you need
to raise it, you *will* know it.

Besides, I'm not sure that it makes sense to let other product needs
dictate the default configurations for this one. It would be one thing
if the vast majority of people only used PostgreSQL with Apache. I know
I'm using it in environments in which no way relate to the web. I'm
thinking I'm not alone.

True, but even so, 32 max connections is a bit light. I have more
pgsql databases than that on my box now. My point in my previous answer
to Tom was that you HAVE to shut down postgresql to change this. It
doesn't allocate tons of semaphores on startup, just when the child
processes are spawned, and I'd rather have the user adjust their OS to
meet the higher need than have to shut down and restart postgresql as
well. This is one of the settings that make it feel like a "toy" when you
first open it.

How many other high quality databases in the whole world restrict max
connections to 32? The original choice of 32 was set because the original
choice of 64 shared memory blocks as the most we could hope for on common
OS installs. Now that we're looking at cranking that up to 1000,
shouldn't max connections get a look too?

You don't have to be using apache to need more than 32 simo connections.
Heck, how many postgresql databases do you figure are in production with
that setting still in there? My guess is not many.

I'm not saying we should do this to make benchmarks better either, I'm
saying we should do it to improve the user experience. A limit of 32
connects makes things tough for a beginning DBA, not only does he find out
the problem while his database is under load the first time, but then he
can't fix it without shutting down and restarting postgresql. If the max
is set to 200 or 500 and he starts running out of semaphores, that's a
problem he can address while his database is still up and running in most
operating systems, at least in the ones I use.

So, my main point is that any setting that requires you to shut down
postgresql to make the change, we should pick a compromise value that
means you never likely will have to shut down the database once you've
started it up and it's under load. shared buffers, max connects, etc...
should not need tweaking for 95% or more of the users if we can help it.
It would be nice if we could find a set of numbers that reduce the number
of problems users have, so all I'm doing is looking for the sweetspot,
which is NOT 32 max connections.


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[Tom Lane]

... The original choice of 32 was set because the original
choice of 64 shared memory blocks as the most we could hope for on common
OS installs. Now that we're looking at cranking that up to 1000,
shouldn't max connections get a look too?

Actually I think max-connections at 32 was set because of SEMMAX limits,
and had only the most marginal connection to shared_buffers (anyone care
to troll the archives to check?) But sure, let's take another look at
the realistic limits today.

... If he starts running out of semaphores, that's a
problem he can address while his database is still up and running in most
operating systems, at least in the ones I use.

Back in the day, this took a kernel rebuild and system reboot to fix.
If this has changed, great ... but on exactly which Unixen can you
alter SEMMAX on the fly?

So, my main point is that any setting that requires you to shut down
postgresql to make the change, we should pick a compromise value that
means you never likely will have to shut down the database once you've
started it up and it's under load.

When I started using Postgres, it did not allocate the max number of
semas it might need at startup, but was instead prone to fail when you
tried to open the 17th or 33rd or so connection. It was universally
agreed to be an improvement to refuse to start at all if we could not
meet the specified max_connections setting. I don't want to backtrack
from that. If we can up the default max_connections setting, great ...
but let's not increase the odds of failing under load.

regards, tom lane

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[scott.marlowe]

Post by Tom Lane

... If he starts running out of semaphores, that's a
problem he can address while his database is still up and running in most
operating systems, at least in the ones I use.

Back in the day, this took a kernel rebuild and system reboot to fix.
If this has changed, great ... but on exactly which Unixen can you
alter SEMMAX on the fly?

Tom, now you're making me all misty eyed for 14" platter 10 Meg hard
drives and paper tape readers. :-)

Seriously, I know Linux can change these on the fly, and I'm pretty sure
Solaris can too. I haven't played with BSD for a while so can't speak
about that. Anyone else know?

Post by Tom Lane

So, my main point is that any setting that requires you to shut down
postgresql to make the change, we should pick a compromise value that
means you never likely will have to shut down the database once you've
started it up and it's under load.

When I started using Postgres, it did not allocate the max number of
semas it might need at startup, but was instead prone to fail when you
tried to open the 17th or 33rd or so connection. It was universally
agreed to be an improvement to refuse to start at all if we could not
meet the specified max_connections setting. I don't want to backtrack
from that. If we can up the default max_connections setting, great ...
but let's not increase the odds of failing under load.

I don't want to backtrack either, and I prefer that we now grab the
semaphores we need at startup.

Note that on a stock RH 72 box, the max number of
backends you can startup before you exhaust semphores is 2047 backends,
more than I'd ever want to try and run on normal PC hardware. So, on a
linux box 150 to 200 max backends comes no where near exhausting
semaphores.

I imagine that any "joe average" who doesn't really understand sysadmin
duties that well and is trying for the first time to install Postgresql
WILL be doing so on one of three general platforms, Linux, BSD, or
Windows. As long as the initial settings use only 10% or so of the file
handle and / or semaphore resources on each of those systems, we're
probably safe.

64 or 128 seems like a nice power of two number that is likely to keep us
safe on inital installs while forestalling problems with too many
connections.

Just for score, here's the default max output of rh72's kernel config:

kernel.sem = 250 32000 32 128
fs.file-max = 8192

Note that while older kernels needed to have max inodes bumped up as well,
nowadays that doesn't seem to be a problem, or they just set it really
high and I can't hit the ceiling on my workstation without swap storms.

the definitions of the kernel.sem line are:

kernel.sem: max_sem_per_id max_sem_total max_ops_sem_call max_sem_ids

I'll try to get FreeBSD running today and see what research I can find on
it, but 5.0 is likely to be a whole new beast for me, so if someone can
tell us what the maxes are by default on different BSDs and what the
settings are in postgresql that can exhaust them that gets us closer.

Like I've said before, anyone running HPUX, Irix, Solaris, or any other
"Industrial Strength Unix" should already know to increase all these
things and likely had to long before Postgresql showed up on their box, so
a setting that keeps pgsql from coming up won't be likely, and if it
happens, they'll most likely know how to handle it.

BSD and Linux users are more likely to contain the group of folks who
don't know all this and don't ever want to (not that all BSD/Linux users
are like that, just that the sub group mostly exists on those platforms,
and windows as well.) So the default settings really probably should be
determined, for the most part, by the needs of those users.


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[Christopher Kings-Lynne]

Post by scott.marlowe
Seriously, I know Linux can change these on the fly, and I'm pretty sure
Solaris can too. I haven't played with BSD for a while so can't speak
about that. Anyone else know?

You cannot change SHMMAX on the fly on FreeBSD.

Chris


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[Larry Rosenman]

--On Thursday, February 13, 2003 09:47:28 +0800 Christopher Kings-Lynne

Post by Christopher Kings-Lynne

Post by scott.marlowe
Seriously, I know Linux can change these on the fly, and I'm pretty sure
Solaris can too. I haven't played with BSD for a while so can't speak
about that. Anyone else know?

You cannot change SHMMAX on the fly on FreeBSD.

Yes you can, on recent 4-STABLE:

Password:
lerlaptop# sysctl kern.ipc.shmmax=66000000
kern.ipc.shmmax: 33554432 -> 66000000
lerlaptop#uname -a
FreeBSD lerlaptop.lerctr.org 4.7-STABLE FreeBSD 4.7-STABLE #38: Mon Feb 3
21:51:25 CST 2003
***@lerlaptop.lerctr.org:/usr/obj/usr/src/sys/LERLAPTOP i386
lerlaptop#

Post by Christopher Kings-Lynne
Chris
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Larry Rosenman http://www.lerctr.org/~ler
Phone: [phone] E-Mail: ***@lerctr.org
US Mail: 1905 Steamboat Springs Drive, Garland, TX 75044-6749




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[Bruce Momjian]

Post by Christopher Kings-Lynne

Post by scott.marlowe
Seriously, I know Linux can change these on the fly, and I'm pretty sure
Solaris can too. I haven't played with BSD for a while so can't speak
about that. Anyone else know?

You cannot change SHMMAX on the fly on FreeBSD.

And part of the reason is because some/most BSD's map the page tables
into physical RAM (kernel space) rather than use some shared page table
mechanism. This is good because it prevents the shared memory from
being swapped out (performance disaster).

It doesn't actually allocate RAM unless someone needs it, but it does
lock the shared memory into a specific fixed location for all processes.

The more flexible approach is to make shared memory act just like the
memory of a user process, and have other user processes share those page
tables, but that adds extra overhead and can cause the memory to behave
just like user memory (swapable).
--
Bruce Momjian | http://candle.pha.pa.us
***@candle.pha.pa.us | [phone]
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073

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[Tom Lane]

Post by Christopher Kings-Lynne
You cannot change SHMMAX on the fly on FreeBSD.

I think we suffered some topic drift here --- wasn't the last question
about whether SEMMAX can be increased on-the-fly? That wouldn't have
anything to do with memory-mapping strategies...

regards, tom lane

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[Curt Sampson]

Post by Bruce Momjian

Post by Christopher Kings-Lynne
You cannot change SHMMAX on the fly on FreeBSD.

And part of the reason is because some/most BSD's map the page tables
into physical RAM (kernel space) rather than use some shared page table
mechanism. This is good because it prevents the shared memory from
being swapped out (performance disaster).

Not at all! In all the BSDs, as far as I'm aware, SysV shared memory is
just normal mmap'd memory.

FreeBSD offers a sysctl that lets you mlock() that memory, and that is
helpful only because postgres insists on taking data blocks that are
already in memory, fully sharable amongst all back ends and ready to be
used, and making a copy of that data to be shared amongst all back ends.

Post by Bruce Momjian
It doesn't actually allocate RAM unless someone needs it, but it does
lock the shared memory into a specific fixed location for all processes.

I don't believe that the shared memory is not locked to a specific VM
address for every process. There's certainly no reason it needs to be.

cjs

[Bruce Momjian]

I was speaking of the 4.4 BSD. FreeBSD has the merged VM, and I think
NetBSD only recently did that. BSD/OS does do the locking by default
and it maps into the kernel address space. I believe FreeBSD has a
sysctl to control locking of SysV memory.

One advantage of having it all at the same VM address is that they can
use the same page tables for virtual address lookups.

---------------------------------------------------------------------------

Post by Curt Sampson

Post by Bruce Momjian

Post by Christopher Kings-Lynne
You cannot change SHMMAX on the fly on FreeBSD.

And part of the reason is because some/most BSD's map the page tables
into physical RAM (kernel space) rather than use some shared page table
mechanism. This is good because it prevents the shared memory from
being swapped out (performance disaster).

Not at all! In all the BSDs, as far as I'm aware, SysV shared memory is
just normal mmap'd memory.
FreeBSD offers a sysctl that lets you mlock() that memory, and that is
helpful only because postgres insists on taking data blocks that are
already in memory, fully sharable amongst all back ends and ready to be
used, and making a copy of that data to be shared amongst all back ends.

Post by Bruce Momjian
It doesn't actually allocate RAM unless someone needs it, but it does
lock the shared memory into a specific fixed location for all processes.

I don't believe that the shared memory is not locked to a specific VM
address for every process. There's certainly no reason it needs to be.
cjs
--
Don't you know, in this new Dark Age, we're all light. --XTC

--
Bruce Momjian | http://candle.pha.pa.us
***@candle.pha.pa.us | [phone]
+ If your life is a hard drive, | 13 Roberts Road
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[Greg Stark]

Post by Bruce Momjian
And part of the reason is because some/most BSD's map the page tables
into physical RAM (kernel space) rather than use some shared page table
mechanism. This is good because it prevents the shared memory from
being swapped out (performance disaster).

Well, it'll only be swapped out if it's not being used...

In any case you can use madvise() to try to avoid that, but it doesn't seem
likely to be a problem since they would probably be the most heavily used
pages in postgres.

[Daniel Kalchev]

Post by scott.marlowe

Post by Greg Copeland
Besides, I'm not sure that it makes sense to let other product needs
dictate the default configurations for this one. It would be one thing
if the vast majority of people only used PostgreSQL with Apache. I know
I'm using it in environments in which no way relate to the web. I'm
thinking I'm not alone.

[...]

Post by scott.marlowe
You don't have to be using apache to need more than 32 simo connections.
Heck, how many postgresql databases do you figure are in production with

that setting still in there? My guess is not many.
I would second this. One of my larger PostgreSQL applications uses Apache,
although it's not typical web server. Apache is restricted to particular
number of processes and it rarely uses too many backends (but one should
consider the possible N databases x M apache processes when using persistent
database connections).

The main connection load on that system however comes from lots of scripts
that run asynchronously and access the same data (collect, analyze, archive
data). Even if database access is serialized as much as possible (at the cost
of performance or wall clock time waste), this load represents sometimes
hunderts of backends.

My opinion too is that increasing the number of connections will benefit more
the first-time experience in usability, rather than in performance boost.

The main trouble is, that more connections require not only more semaphores,
but also more shared memory.

If we are toying with the 'performance' idea, we should definitely increase
the sort memory default as well :-) ... and this means LOTS of memory for many
processes.

Is it possible to have some useful connections/memory usage statistics - run
this code on different installations and collect sufficient data to make
better choice.

Daniel


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[scott.marlowe]

Post by Tom Lane

Post by scott.marlowe
Is setting the max connections to something like 200 reasonable, or likely
to cause too many problems?

That would likely run into number-of-semaphores limitations (SEMMNI,
SEMMNS). We do not seem to have as good documentation about changing
that as we do about changing the SHMMAX setting, so I'm not sure I want
to buy into the "it's okay to expect people to fix this before they can
start Postgres the first time" argument here.
Also, max-connections doesn't silently skew your testing: if you need
to raise it, you *will* know it.

True, but unfortunately, the time you usually learn that the first time is
when your web server starts issuing error messages about not being able to
connect to the database. i.e. it fails at the worst possible time.

OK. I just did some very simple testing in RH Linux 7.2 and here's what I
found about file handles: default max appears to be 8192 now, not 4096.

With max file handles set to 4096, I run out of handles when opening about
450 or more simultaneous connections. At 8192, the default for RH72, I
pretty much run out of memory on a 512 Meg box and start swapping
massively long before I can exhaust the file handle pool.

At 200 connections, I use about half of all my file descriptors out of
4096, which seems pretty safe to me.

Note that setting the max connections to 200 in the conf does NOT result
in huge allocations of file handles right away, but only while the
database is under load, so this leads us to the other possible problem,
that the database will exhaust file handles if we set this number too
high, as opposed to not being able to connect because it's too low.

I'm guessing that 200 or less is pretty safe on most modern flavors of
Unix, but I'm not one of those folks who keeps the older flavors happy
really, so I can't speak for them.

Back in the day, a P100 with 30 or 40 connections was a heavy load,
nowadays, a typical workstation has 512 Meg ram or more, and a 1.5+GHz
CPU, so I can see increasing this setting too. I'd rather the only issue
for the user be adjusting their kernel than having to up the connection
limit in postgresql. I can up the max file handles in Linux on the fly,
with no one noticeing it, I have to stop and restart postgresql to make
the max backends take affect, so that's another reason not to have too low
a limit.

Is there a place on the web somewhere that lists the default settings for
most major unixes for file handles, inodes, and shared memory?


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[Tatsuo Ishii]

Post by scott.marlowe
My other pet peeve is the default max connections setting. This should be
higher if possible, but of course, there's always the possibility of
running out of file descriptors.
Apache has a default max children of 150, and if using PHP or another
language that runs as an apache module, it is quite possible to use up all
the pgsql backend slots before using up all the apache child slots.
Is setting the max connections to something like 200 reasonable, or likely
to cause too many problems?

It likely. First you will ran out kernel file descriptors. This could
be solved by increasing the kernel table or lowering
max_files_per_process, though. Second the total throughput will
rapidly descrease if you don't have enough RAM and many
CPUs. PostgreSQL can not handle many concurrent
connections/transactions effectively. I recommend to employ some kind
of connection pooling software and lower the max connections.
--
Tatsuo Ishii

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[scott.marlowe]

Post by Tatsuo Ishii

Post by scott.marlowe
My other pet peeve is the default max connections setting. This should be
higher if possible, but of course, there's always the possibility of
running out of file descriptors.
Apache has a default max children of 150, and if using PHP or another
language that runs as an apache module, it is quite possible to use up all
the pgsql backend slots before using up all the apache child slots.
Is setting the max connections to something like 200 reasonable, or likely
to cause too many problems?

It likely. First you will ran out kernel file descriptors. This could
be solved by increasing the kernel table or lowering
max_files_per_process, though. Second the total throughput will
rapidly descrease if you don't have enough RAM and many
CPUs. PostgreSQL can not handle many concurrent
connections/transactions effectively. I recommend to employ some kind
of connection pooling software and lower the max connections.

Don't know if you saw my other message, but increasing max connects to 200
used about 10% of all my semaphores and about 10% of my file handles.
That was while running pgbench to create 200 simo sessions.

Keep in mind, on my fairly small intranet database server, I routinely
have >32 connections, most coming from outside my webserver. Probably no
more than 4 or 5 connects at a time come from there. These are all things
like Windows boxes with ODBC running access or something similar. Many of
the connections are idle 98% of the time, and use little or no real
resources, even getting swapped out should the server need the spare
memory (it doesn't :-) that machine is set to 120 max simos if I remember
correctly.

while 200 may seem high, 32 definitely seems low. So, what IS a good
compromise? for this and ALL the other settings that should probably be a
bit higher. I'm guessing sort_mem or 4 or 8 meg hits the knee for most
folks, and the max fsm settings tom has suggested make sense.

What wal_sync method should we make default? Or should we pick one based
on the OS the user is running?



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[Tatsuo Ishii]

Post by scott.marlowe

Post by Tatsuo Ishii
It likely. First you will ran out kernel file descriptors. This could
be solved by increasing the kernel table or lowering
max_files_per_process, though. Second the total throughput will
rapidly descrease if you don't have enough RAM and many
CPUs. PostgreSQL can not handle many concurrent
connections/transactions effectively. I recommend to employ some kind
of connection pooling software and lower the max connections.

Don't know if you saw my other message, but increasing max connects to 200
used about 10% of all my semaphores and about 10% of my file handles.
That was while running pgbench to create 200 simo sessions.

I'm not talking about semaphores. You see the low usage of file
descriptors is just because pgbench uses very few tables.

Post by scott.marlowe
Keep in mind, on my fairly small intranet database server, I routinely
have >32 connections, most coming from outside my webserver. Probably no
more than 4 or 5 connects at a time come from there. These are all things
like Windows boxes with ODBC running access or something similar. Many of
the connections are idle 98% of the time, and use little or no real
resources, even getting swapped out should the server need the spare
memory (it doesn't :-) that machine is set to 120 max simos if I remember
correctly.
while 200 may seem high, 32 definitely seems low. So, what IS a good
compromise? for this and ALL the other settings that should probably be a
bit higher. I'm guessing sort_mem or 4 or 8 meg hits the knee for most
folks, and the max fsm settings tom has suggested make sense.

32 is not too low if the kernel file descriptors is not
increased. Beware that running out of the kernel file descriptors is a
serious problem for the entire system, not only for PostgreSQL.

Post by scott.marlowe
What wal_sync method should we make default? Or should we pick one based
on the OS the user is running?

It's really depending on the OS or kernel version. I saw open_sync is
best for certain version of Linux kernel, while fdatasync is good for
another version of kernel. I'm not sure, but it could be possible that
the file system type might affect the wal_sync choice.
--
Tatsuo Ishii

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[Robert Treat]

Post by Tatsuo Ishii

Post by scott.marlowe
while 200 may seem high, 32 definitely seems low. So, what IS a good
compromise? for this and ALL the other settings that should probably be a
bit higher. I'm guessing sort_mem or 4 or 8 meg hits the knee for most
folks, and the max fsm settings tom has suggested make sense.

32 is not too low if the kernel file descriptors is not
increased. Beware that running out of the kernel file descriptors is a
serious problem for the entire system, not only for PostgreSQL.

Had this happen at a previous employer, and it definitely is bad. I
believe we had to do a reboot to clear it up. And we saw the problem a
couple of times since the sys admin wasn't able to deduce what had
happened the first time we got it. IIRC the problem hit somewhere around
150 connections, so we ran with 128 max. I think this is a safe number
on most servers these days (running linux as least) though out of the
box I might be more inclined to limit it to 64. If you do hit a file
descriptor problem, *you are hosed*.

Robert Treat



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[Greg Copeland]

Post by Robert Treat

Post by Tatsuo Ishii

Post by scott.marlowe
while 200 may seem high, 32 definitely seems low. So, what IS a good
compromise? for this and ALL the other settings that should probably be a
bit higher. I'm guessing sort_mem or 4 or 8 meg hits the knee for most
folks, and the max fsm settings tom has suggested make sense.

32 is not too low if the kernel file descriptors is not
increased. Beware that running out of the kernel file descriptors is a
serious problem for the entire system, not only for PostgreSQL.

Had this happen at a previous employer, and it definitely is bad. I
believe we had to do a reboot to clear it up. And we saw the problem a
couple of times since the sys admin wasn't able to deduce what had
happened the first time we got it. IIRC the problem hit somewhere around
150 connections, so we ran with 128 max. I think this is a safe number
on most servers these days (running linux as least) though out of the
box I might be more inclined to limit it to 64. If you do hit a file
descriptor problem, *you are hosed*.

That does seem like a more reasonable upper limit. I would rather see
people have to knowingly increase the limit rather than bump into system
upper limits and start scratching their heads trying to figure out what
the heck is going on.

[Tom Lane]

Post by Robert Treat
Had this happen at a previous employer, and it definitely is bad. I
believe we had to do a reboot to clear it up. And we saw the problem a
couple of times since the sys admin wasn't able to deduce what had
happened the first time we got it. IIRC the problem hit somewhere around
150 connections, so we ran with 128 max. I think this is a safe number
on most servers these days (running linux as least) though out of the
box I might be more inclined to limit it to 64. If you do hit a file
descriptor problem, *you are hosed*.

If you want to run lots of connections, it's a real good idea to set
max_files_per_process to positively ensure Postgres won't overflow
your kernel file table, ie, max_connections * max_files_per_process
should be less than the file table size.

Before about 7.2, we didn't have max_files_per_process, and would
naively believe whatever sysconf() told us was an okay number of files
to open. Unfortunately, way too many kernels promise more than they
can deliver ...

regards, tom lane

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[scott.marlowe]

Oh, another setting that should be a "default" for most users is to initdb
automatically with locale of C. If they need a different locale, they
should have to pick it.

The performance of Postgresql with a locale other than C when doing like
and such is a serious ding. I'd much rather have the user experience the
faster searches first, then get to test with other locales and see if
performance is good enough, than to start out slow and wonder why they
need to change their initdb settings to get decent performance on a where
clause with like in it.


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[Christopher Kings-Lynne]

Post by Robert Treat
Had this happen at a previous employer, and it definitely is bad. I
believe we had to do a reboot to clear it up. And we saw the problem a
couple of times since the sys admin wasn't able to deduce what had
happened the first time we got it. IIRC the problem hit somewhere around
150 connections, so we ran with 128 max. I think this is a safe number
on most servers these days (running linux as least) though out of the
box I might be more inclined to limit it to 64. If you do hit a file
descriptor problem, *you are hosed*.

Just yesterday I managed to hose my new Postgres installation during a
particular benchmarking run. Postgres did restart itself nicely though. I
have no idea why that particular run caused problems when all other runs
with identical settings didn't. I checked the log and saw file descriptor
probs. I was doing 128 connections with 128 max connetions. This was the

Post by Robert Treat
2003-02-12 04:16:15 LOG: PGSTAT: cannot open temp stats file
/usr/local/pgsql/data/global/pgstat.tmp.41388: Too many open files in
system
2003-02-12 04:16:15 LOG: PGSTAT: cannot open temp stats file
/usr/local/pgsql/data/global/pgstat.tmp.41388: Too many open files in
system
2003-02-12 04:16:39 PANIC: could not open transaction-commit log
directory
(/usr/local/pgsql/data/pg_clog): Too many open files in system
2003-02-12 04:16:39 LOG: statement: SET autocommit TO 'on';VACUUM
ANALYZE
2003-02-12 04:16:39 LOG: PGSTAT: cannot open temp stats file
/usr/local/pgsql/data/global/pgstat.tmp.41388: Too many open files in
system
kern.maxfiles: 1064
kern.maxfilesperproc: 957
sysctl -w kern.maxfiles=65536
sysctl -w kern.maxfilesperproc=8192
.. and then stick
kern.maxfiles=65536
kern.maxfilesperproc=8192
in /etc/sysctl.conf so its set during a reboot.

Which just goes to highlight the importance of rigorously testing a
production installation...

Chris





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[Tom Lane]

Post by mlw
This attitude sucks. If you want a product to be used, you must put the
effort into making it usable.
[snip]

AFAICT, you are flaming Greg for recommending the exact same thing you
are recommending. Please calm down and read again.

regards, tom lane

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[Christopher Kings-Lynne]

Post by mlw

Post by Greg Copeland
After it's all said and done, I would rather someone simply say, "it's
beyond my skill set", and attempt to get help or walk away. That seems
better than them being able to run it and say, "it's a dog", spreading
word-of-mouth as such after they left PostgreSQL behind. Worse yet,
those that do walk away and claim it performs horribly are probably
doing more harm to the PostgreSQL community than expecting someone to be
able to install software ever can.

<RANT>
And that my friends is why PostgreSQL is still relatively obscure.

Dude - I hang out on PHPBuilder's database forums and you wouldn't believe
how often the "oh, don't use Postgres, it has a history of database
corruption problems" thing is mentioned.

Chris



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[Rick Gigger]

Post by Greg Copeland

Post by Tom Lane

Post by Merlin Moncure
May I make a suggestion that maybe it is time to start thinking about
tuning the default config file, IMHO its just a little bit too
conservative,

It's a lot too conservative. I've been thinking for awhile that we
should adjust the defaults.
The original motivation for setting shared_buffers = 64 was so that
Postgres would start out-of-the-box on machines where SHMMAX is 1 meg
(64 buffers = 1/2 meg, leaving 1/2 meg for our other shared data
structures). At one time SHMMAX=1M was a pretty common stock kernel
setting. But our other data structures blew past the 1/2 meg mark
some time ago; at default settings the shmem request is now close to
1.5 meg. So people with SHMMAX=1M have already got to twiddle their
postgresql.conf settings, or preferably learn how to increase SHMMAX.
That means there is *no* defensible reason anymore for defaulting to
64 buffers.
We could retarget to try to stay under SHMMAX=4M, which I think is
the next boundary that's significant in terms of real-world platforms
(isn't that the default SHMMAX on some BSDen?). That would allow us
350 or so shared_buffers, which is better, but still not really a
serious choice for production work.
What I would really like to do is set the default shared_buffers to
1000. That would be 8 meg worth of shared buffer space. Coupled with
more-realistic settings for FSM size, we'd probably be talking a shared
memory request approaching 16 meg. This is not enough RAM to bother
any modern machine from a performance standpoint, but there are probably
quite a few platforms out there that would need an increase in their
stock SHMMAX kernel setting before they'd take it.
So what this comes down to is making it harder for people to get
Postgres running for the first time, versus making it more likely that
they'll see decent performance when they do get it running.
It's worth noting that increasing SHMMAX is not nearly as painful as
it was back when these decisions were taken. Most people have moved
to platforms where it doesn't even take a kernel rebuild, and we've
acquired documentation that tells how to do it on all(?) our supported
platforms. So I think it might be okay to expect people to do it.
The alternative approach is to leave the settings where they are, and
to try to put more emphasis in the documentation on the fact that the
factory-default settings produce a toy configuration that you *must*
adjust upward for decent performance. But we've not had a lot of
success spreading that word, I think. With SHMMMAX too small, you
do at least get a pretty specific error message telling you so.
Comments?

I'd personally rather have people stumble trying to get PostgreSQL
running, up front, rather than allowing the lowest common denominator
more easily run PostgreSQL only to be disappointed with it and move on.
After it's all said and done, I would rather someone simply say, "it's
beyond my skill set", and attempt to get help or walk away. That seems
better than them being able to run it and say, "it's a dog", spreading
word-of-mouth as such after they left PostgreSQL behind. Worse yet,
those that do walk away and claim it performs horribly are probably
doing more harm to the PostgreSQL community than expecting someone to be
able to install software ever can.
"Easy to install but is horribly slow."
or
"Took a couple of minutes to configure and it rocks!"
Seems fairly cut-n-dry to me. ;)

The type of person who can't configure it or doesnt' think to try is
probably not doing a project that requires any serious performance. As long
as you are running it on decent hardware postgres will run fantastic for
anything but a very heavy load. I think there may be many people out there
who have little experience but want an RDBMS to manage their data. Those
people need something very, very easy. Look at the following that mysql
gets despite how poor of a product it is. It's very, very easy. Mysql
works great for many peoples needs but then when they need to do something
real they need to move to a different database entirely. I think there is a
huge advantage to having a product that can be set up very quickly out of
the box. Those who need serious performance, hopefully for ther employers
sake, will be more like to take a few minutes to do some quick performance
tuning.

Rick Gigger


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[scott.marlowe]

Post by Rick Gigger
The type of person who can't configure it or doesnt' think to try is
probably not doing a project that requires any serious performance. As long
as you are running it on decent hardware postgres will run fantastic for
anything but a very heavy load. I think there may be many people out there
who have little experience but want an RDBMS to manage their data. Those
people need something very, very easy. Look at the following that mysql
gets despite how poor of a product it is. It's very, very easy. Mysql
works great for many peoples needs but then when they need to do something
real they need to move to a different database entirely. I think there is a
huge advantage to having a product that can be set up very quickly out of
the box. Those who need serious performance, hopefully for ther employers
sake, will be more like to take a few minutes to do some quick performance
tuning.

Very good point. I'm pushing for changes that will NOT negatively impact
joe beginner on the major platforms (Linux, BSD, Windows) in terms of
install. I figure anyone installing on big iron already knows enough
about their OS we don't have to worry about shared buffers being too big
for that machine.

So, a compromise of faster performance out of the box, with little or no
negative user impact seems the sweet spot here.

I'm thinking a good knee setting for each one, where not too much memory /
semaphores / file handles get gobbled up, but the database isn't pokey.

The poor performance of Postgresql in it's current default configuration
HAS cost us users, trust me, I know a few we've almost lost where I work
that I converted after some quick tweaking of their database.

In it's stock form Postgresql is very slow at large simple queries, like
'select * from table1 t1 natural join table2 t2 where t1.field='a'; where
you get back something like 10,000 rows. The real bottleneck here is
sort_mem. A simple bump up to 8192 or so makes the database much more
responsive.

If we're looking at changing default settings for 7.4, then we should look
at changing ALL of them that matter, since we'll have the most time to
shake out problems if we do them early, and we won't have four or five
rounds of setting different defaults over time and finding the limitations
of the HOST OSes one at a time.


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[Bruno Wolff III]

On Tue, Feb 11, 2003 at 17:42:06 -0700,

Post by scott.marlowe
The poor performance of Postgresql in it's current default configuration
HAS cost us users, trust me, I know a few we've almost lost where I work
that I converted after some quick tweaking of their database.

About two years ago I talked some people into trying it at work to
use with IMP/Horde which had been having some corruption problems
while using MySQL (though it wasn't necessarily a problem with MySQL).
I told them to be sure to use 7.1. When they tried it out it couldn't
keep up with the load. I asked the guys what they tried and found out
they couldn't find 7.1 rpms and didn't want to compile from source and
so ended up using 7.0.?. Also as far as I could tell from talking to them,
they didn't do any tuning at all. They weren't interested in taking another
look at it after that. We are still using MySQL with that system today.

One of our DBAs is using it for some trial projects (including one for me)
even though we have a site license for Oracle.

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[Andrew Sullivan]

Post by Rick Gigger
The type of person who can't configure it or doesnt' think to try is
probably not doing a project that requires any serious performance.

I have piles of email, have fielded thousands of phone calls, and
have had many conversations which prove that claim false. People
think that computers are magic. That they don't think the machines
require a little bit of attention is nowise an indication that they
don't need the system to come with reasonable defaults.

A
--
----
Andrew Sullivan 204-4141 Yonge Street
Liberty RMS Toronto, Ontario Canada
<***@libertyrms.info> M2P 2A8
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[Rod Taylor]

Post by Andrew Sullivan

Post by Rick Gigger
The type of person who can't configure it or doesnt' think to try is
probably not doing a project that requires any serious performance.

I have piles of email, have fielded thousands of phone calls, and
have had many conversations which prove that claim false. People

But IBM told me computers are self healing, so if there is a performance
problem should it just fix itself?

[Patrick Welche]

On Tue, Feb 11, 2003 at 11:20:14AM -0500, Tom Lane wrote:
...

Post by Tom Lane
We could retarget to try to stay under SHMMAX=4M, which I think is
the next boundary that's significant in terms of real-world platforms
(isn't that the default SHMMAX on some BSDen?).

...

Assuming 1 page = 4k, and number of pages is correct in GENERIC kernel configs,
SHMMAX=4M for NetBSD (8M for i386, x86_64)

Cheers,

Patrick

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[Justin Clift]

Tom Lane wrote:
<snip>

Post by Tom Lane
What I would really like to do is set the default shared_buffers to
1000. That would be 8 meg worth of shared buffer space. Coupled with
more-realistic settings for FSM size, we'd probably be talking a shared
memory request approaching 16 meg. This is not enough RAM to bother
any modern machine from a performance standpoint, but there are probably
quite a few platforms out there that would need an increase in their
stock SHMMAX kernel setting before they'd take it.

<snip>

Totally agree with this. We really, really, really, really need to get
the default to a point where we have _decent_ default performance.

Post by Tom Lane
The alternative approach is to leave the settings where they are, and
to try to put more emphasis in the documentation on the fact that the
factory-default settings produce a toy configuration that you *must*
adjust upward for decent performance. But we've not had a lot of
success spreading that word, I think. With SHMMMAX too small, you
do at least get a pretty specific error message telling you so.
Comments?

Yep.

Here's an *unfortunately very common* scenario, that again
unfortunately, a _seemingly large_ amount of people fall for.

a) Someone decides to "benchmark" database XYZ vs PostgreSQL vs other
databases

b) Said benchmarking person knows very little about PostgreSQL, so they
install the RPM's, packages, or whatever, and "it works". Then they run
whatever benchmark they've downloaded, or designed, or whatever

c) PostgreSQL, being practically unconfigured, runs at the pace of a
slow, mostly-disabled snail.

d) Said benchmarking person gets better performance from the other
databases (also set to their default settings) and thinks "PostgreSQL
has lots of features, and it's free, but it's Too Slow".

Yes, this kind of testing shouldn't even _pretend_ to have any real
world credibility.

e) Said benchmarking person tells everyone they know, _and_ everyone
they meet about their results. Some of them even create nice looking or
profesional looking web pages about it.

f) People who know even _less_ than the benchmarking person hear about
the test, or read the result, and don't know any better than to believe
it at face value. So, they install whatever system was recommended.

g) Over time, the benchmarking person gets the hang of their chosen
database more and writes further articles about it, and doesn't
generally look any further afield than it for say... a couple of years.
By this time, they've already influenced a couple of thousand people
in the non-optimal direction.

h) Arrgh. With better defaults, our next release would _appear_ to be a
lot faster to quite a few people, just because they have no idea about
tuning.

So, as sad as this scenario is, better defaults will probably encourage
a lot more newbies to get involved, and that'll eventually translate
into a lot more experienced users, and a few more coders to assist. ;-)

Personally I'd be a bunch happier if we set the buffers so high that we
definitely have decent performance, and the people that want to run
PostgreSQL are forced to make the choice of either:

1) Adjust their system settings to allow PostgreSQL to run properly, or

2) Manually adjust the PostgreSQL settings to run memory-constrained

This way, PostgreSQL either runs decently, or they are _aware_ that
they're limiting it. That should cut down on the false benchmarks
(hopefully).

:-)

Regards and best wishes,

Justin Clift

Post by Tom Lane
regards, tom lane

--
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
- Indira Gandhi


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[Tom Lane]

Post by Justin Clift
Personally I'd be a bunch happier if we set the buffers so high that we
definitely have decent performance, and the people that want to run
1) Adjust their system settings to allow PostgreSQL to run properly, or
2) Manually adjust the PostgreSQL settings to run memory-constrained
This way, PostgreSQL either runs decently, or they are _aware_ that
they're limiting it.

Yeah, that is the subtext here. If you can't increase SHMMAX then you
can always trim the postgresql.conf parameters --- but theoretically,
at least, you should then have a clue that you're running a
badly-configured setup ...

regards, tom lane

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[Josh Berkus]

Tom, Justin,

Post by Tom Lane
What I would really like to do is set the default shared_buffers to
1000. That would be 8 meg worth of shared buffer space. Coupled with
more-realistic settings for FSM size, we'd probably be talking a shared
memory request approaching 16 meg. This is not enough RAM to bother
any modern machine from a performance standpoint, but there are probably
quite a few platforms out there that would need an increase in their
stock SHMMAX kernel setting before they'd take it.

What if we supplied several sample .conf files, and let the user choose which
to copy into the database directory? We could have a "high read
performance" profile, and a "transaction database" profile, and a
"workstation" profile, and a "low impact" profile. We could even supply a
Perl script that would adjust SHMMAX and SHMMALL on platforms where this can
be done from the command line.

[Kaare Rasmussen]

Post by Josh Berkus
What if we supplied several sample .conf files, and let the user choose
which to copy into the database directory? We could have a "high read

Exactly my first thought when reading the proposal for a setting suited for
performance tests.

Post by Josh Berkus
performance" profile, and a "transaction database" profile, and a
"workstation" profile, and a "low impact" profile. We could even supply a

And a .benchmark profile :-)

Post by Josh Berkus
Perl script that would adjust SHMMAX and SHMMALL on platforms where this
can be done from the command line.

Or maybe configuration could be adjusted with ./configure if SHMMAX can be
determined at that point?
--
Kaare Rasmussen --Linux, spil,-- Tlf: 3816 2582
Kaki Data tshirts, merchandize Fax: [phone]
Howitzvej 75 Åben 12.00-18.00 Email: ***@kakidata.dk
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[Justin Clift]

Post by Josh Berkus
Tom, Justin,

<snip>

Post by Josh Berkus
What if we supplied several sample .conf files, and let the user choose which
to copy into the database directory? We could have a "high read
performance" profile, and a "transaction database" profile, and a
"workstation" profile, and a "low impact" profile. We could even supply a
Perl script that would adjust SHMMAX and SHMMALL on platforms where this can
be done from the command line.

This might have value as the next step in the process of:

a) Are we going to have better defaults?

or

b) Let's stick with the current approach.


If we decide to go with better (changed) defaults, we may also be able
to figure out a way of having profiles that could optionally be chosen from.

As a longer term thought, it would be nice if the profiles weren't just
hard-coded example files, but more of:

pg_autotune --setprofile=xxx

Or similar utility, and it did all the work. Named profiles being one
capability, and other tuning measurements (i.e. cpu costings, disk
performance profiles, etc) being the others.

Regards and best wishes,

Justin Clift
--
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
- Indira Gandhi


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[Tom Lane]

Post by Josh Berkus
What if we supplied several sample .conf files, and let the user choose which
to copy into the database directory? We could have a "high read
performance" profile, and a "transaction database" profile, and a
"workstation" profile, and a "low impact" profile.

Uh ... do we have a basis for recommending any particular sets of
parameters for these different scenarios? This could be a good idea
in the abstract, but I'm not sure I know enough to fill in the details.

A lower-tech way to accomplish the same result is to document these
alternatives in postgresql.conf comments and encourage people to review
that file, as Steve Crawford just suggested. But first we need the raw
knowledge.

regards, tom lane

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[Justin Clift]

Tom Lane wrote:
<snip>

Post by Tom Lane
Uh ... do we have a basis for recommending any particular sets of
parameters for these different scenarios? This could be a good idea
in the abstract, but I'm not sure I know enough to fill in the details.
A lower-tech way to accomplish the same result is to document these
alternatives in postgresql.conf comments and encourage people to review
that file, as Steve Crawford just suggested. But first we need the raw
knowledge.

Without too much hacking around, you could pretty easily adapt the
pg_autotune code to do proper profiles of a system with different settings.

i.e. increment one setting at a time, run pgbench on it with some decent
amount of transactions and users, stuff the results into a different
database. Aggregate data over time kind of thing. Let it run for a
week, etc.

If it's helpful, there's a 100% spare Althon 1.6Ghz box around with
(choose your OS) + Adaptec 29160 + 512MB RAM + 2 x 9GB Seagate Cheetah
10k rpm drives hanging around. No stress to set that up and let it run
any long terms tests you'd like plus send back results.

Regards and best wishes,

Justin Clift

Post by Tom Lane
regards, tom lane

[Josh Berkus]

Tom, Justin,

Post by Justin Clift

Post by Tom Lane
Uh ... do we have a basis for recommending any particular sets of
parameters for these different scenarios? This could be a good idea
in the abstract, but I'm not sure I know enough to fill in the details.

Sure.
Mostly-Read database, few users, good hardware, complex queries:
= High shared buffers and sort mem, high geqo and join collapse thresholds,
moderate fsm settings, defaults for WAL.
Same as above with many users and simple queries (webserver) =
same as above, except lower sort mem and higher connection limit
High-Transaction Database =
Moderate shared buffers and sort mem, high FSM settings, increase WAL files
and buffers.
Workstation =
Moderate to low shared buffers and sort mem, moderate FSM, defaults for WAL,
etc.
Low-Impact server = current defaults, more or less.

While none of these settings will be *perfect* for anyone, they will be
considerably better than what's shipping with postgresql. And, based on my
"Learning Perl" knowledge, I'm pretty sure I could write the program.

All we'd need to do is argue out, on the PERFORMANCE list, what's a good value
for each profile. That's the tough part. The Perl script is easy.

Post by Justin Clift

Post by Tom Lane
A lower-tech way to accomplish the same result is to document these
alternatives in postgresql.conf comments and encourage people to review
that file, as Steve Crawford just suggested. But first we need the raw
knowledge.

That's also not a bad approach ... the CONF file should be more heavily
commented, period, regardless of what approach we take. I volunteer to work
on this with other participants.

Post by Justin Clift
Without too much hacking around, you could pretty easily adapt the
pg_autotune code to do proper profiles of a system with different settings.

No offense, Justin, but I don't know anyone else who's gotten your pg_autotune
script to run other than you. And pg_bench has not been useful performance
measure for any real database server I have worked on so far.

I'd be glad to help improve pg_autotune, with two caveats:
1) We will still need to figure out the "profiles" above so that we have
decent starting values.
2) I suggest that we do pg_autotune in Perl or Python or another higher-level
language. This would enable several performance buffs who don't do C to
contribute to it, and a performance-tuning script is a higher-level-language
sort of function, anyway.

[Kevin Brown]

Post by Josh Berkus

Post by Tom Lane
Uh ... do we have a basis for recommending any particular sets of
parameters for these different scenarios? This could be a good idea
in the abstract, but I'm not sure I know enough to fill in the details.

Sure.
= High shared buffers and sort mem, high geqo and join collapse thresholds,
moderate fsm settings, defaults for WAL.
Same as above with many users and simple queries (webserver) =
same as above, except lower sort mem and higher connection limit
High-Transaction Database =
Moderate shared buffers and sort mem, high FSM settings, increase WAL files
and buffers.
Workstation =
Moderate to low shared buffers and sort mem, moderate FSM, defaults for WAL,
etc.
Low-Impact server = current defaults, more or less.

Okay, but there should probably be one more, called "Benchmark". The
real problem is what values to use for it. :-)

[Christopher Kings-Lynne]

OK,

Here's a stab at some extra conf files. Feel free to shoot them down.

If we can come up with at least _some_ alternative files that we can put
somewhere for them to see when postgres is installed, then at least people
can see what variables will affect what...

I didn't see the point of a 'workstation' option, the default is fine for
that.

Chris

-----Original Message-----
Sent: Friday, 14 February 2003 11:26 AM
[pgsql-advocacy]

Post by Josh Berkus

Post by Tom Lane
Uh ... do we have a basis for recommending any particular sets of
parameters for these different scenarios? This could be a good idea
in the abstract, but I'm not sure I know enough to fill in

the details.

Post by Josh Berkus
Sure.
= High shared buffers and sort mem, high geqo and join

collapse thresholds,

Post by Josh Berkus
moderate fsm settings, defaults for WAL.
Same as above with many users and simple queries (webserver) =
same as above, except lower sort mem and higher connection limit
High-Transaction Database =
Moderate shared buffers and sort mem, high FSM settings,

increase WAL files

Post by Josh Berkus
and buffers.
Workstation =
Moderate to low shared buffers and sort mem, moderate FSM,

defaults for WAL,

Post by Josh Berkus
etc.
Low-Impact server = current defaults, more or less.

Okay, but there should probably be one more, called "Benchmark". The
real problem is what values to use for it. :-)
--
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[Manfred Koizar]

On Fri, 14 Feb 2003 14:12:50 +0800, "Christopher Kings-Lynne"

Post by Christopher Kings-Lynne
Here's a stab at some extra conf files. Feel free to shoot them down.

No intent to shoot anything down, just random thoughts:

effective_cache_size = 20000 (~ 160 MB) should be more adequate for a
256 MB machine than the extremely conservative default of 1000. I
admit that the effect of this change is hard to benchmark. A way too
low (or too high) setting may lead the planner to wrong conclusions.

More parameters affecting the planner:
#cpu_tuple_cost = 0.01
#cpu_index_tuple_cost = 0.001
#cpu_operator_cost = 0.0025

Are these still good defaults? I have no hard facts, but ISTM that
CPU speed is increasing more rapidly than disk access speed.

In postgresql.conf.sample-writeheavy you have:
commit_delay = 10000

Is this still needed with "ganged WAL writes"? Tom?

Servus
Manfred

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[Daniel Kalchev]

Post by Manfred Koizar
effective_cache_size = 20000 (~ 160 MB) should be more adequate for a
256 MB machine than the extremely conservative default of 1000. I
admit that the effect of this change is hard to benchmark. A way too
low (or too high) setting may lead the planner to wrong conclusions.

The default on BSD systems is 10% of the total RAM, so on a 256MB machine this
would be ~26MB or effective_cache_size = 32000.

One could always modify the kernel to support much larger value, but I doubt
this is done in many cases and the usefulness of larger buffer cache is not
obvious in the presence of many fsync calls (which might be typicall). I could
be wrong, of course :)

In any case, the default is indeed low and would prevent using indexes on
larger tables, where they are most useful.

Daniel


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[Tom Lane]

Post by Justin Clift

Post by Tom Lane
Uh ... do we have a basis for recommending any particular sets of
parameters for these different scenarios? This could be a good idea
in the abstract, but I'm not sure I know enough to fill in the details.

Without too much hacking around, you could pretty easily adapt the
pg_autotune code to do proper profiles of a system with different settings.
i.e. increment one setting at a time, run pgbench on it with some decent
amount of transactions and users, stuff the results into a different
database.

If I thought that pgbench was representative of anything, or even
capable of reliably producing repeatable numbers, then I might subscribe
to results derived this way. But I have little or no confidence in
pgbench. Certainly I don't see how you'd use it to produce
recommendations for a range of application scenarios, when it's only
one very narrow scenario itself.

regards, tom lane

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[Tatsuo Ishii]

Post by Tom Lane
If I thought that pgbench was representative of anything, or even
capable of reliably producing repeatable numbers, then I might subscribe
to results derived this way. But I have little or no confidence in
pgbench. Certainly I don't see how you'd use it to produce
recommendations for a range of application scenarios, when it's only
one very narrow scenario itself.

Sigh. People always complain "pgbench does not reliably producing
repeatable numbers" or something then say "that's because pgbench's
transaction has too much contention on the branches table". So I added
-N option to pgbench which makes pgbench not to do any UPDATE to
the branches table. But still people continue to complian...

There should be many factors that would produce non-repeatable
results exist, for instance kenel buffer, PostgreSQL's buffer manager,
pgbench itself etc. etc... So far it seems no one has ever made clean
explanation why non-repeatable results happen...
--
Tatsuo Ishii

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[Josh Berkus]

Tatsuo,

Post by Tatsuo Ishii
Sigh. People always complain "pgbench does not reliably producing
repeatable numbers" or something then say "that's because pgbench's
transaction has too much contention on the branches table". So I added
-N option to pgbench which makes pgbench not to do any UPDATE to
the branches table. But still people continue to complian...

Hey, pg_bench is a good start on a Postgres performance tester, and it's much,
much better than what there was before you came along ... which was nothing.
Thank you again for contributing it.

pg_bench is, however, only a start on a performance tester, and we'd need to
build it up before we could use it as the basis of a PG tuner.

[Shridhar Daithankar]

Post by Tom Lane

Post by Josh Berkus
What if we supplied several sample .conf files, and let the user choose
which to copy into the database directory? We could have a "high read
performance" profile, and a "transaction database" profile, and a
"workstation" profile, and a "low impact" profile.

Uh ... do we have a basis for recommending any particular sets of
parameters for these different scenarios? This could be a good idea
in the abstract, but I'm not sure I know enough to fill in the details.

Let's take very simple scenario to supply pre-configured postgresql.conf.

Assume that SHMMAX=Total memory/2 and supply different config files for

64MB/128Mb/256MB/512MB and above.

Is it simple enough?

Shridhar

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[Robert Treat]

Post by Justin Clift
b) Said benchmarking person knows very little about PostgreSQL, so they
install the RPM's, packages, or whatever, and "it works". Then they run
whatever benchmark they've downloaded, or designed, or whatever

Out of curiosity, how feasible is it for the rpm/package/deb/exe
maintainers to modify their supplied postgresql.conf settings when
building said distribution? AFAIK the minimum default SHHMAX setting on
Red Hat 8.0 is 32MB, seems like bumping shared buffers to work with that
amount would be acceptable inside the 8.0 rpm's.

Robert Treat




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[Lamar Owen]

Post by Robert Treat

Post by Justin Clift
b) Said benchmarking person knows very little about PostgreSQL, so they
install the RPM's, packages, or whatever, and "it works". Then they run
whatever benchmark they've downloaded, or designed, or whatever

Out of curiosity, how feasible is it for the rpm/package/deb/exe
maintainers to modify their supplied postgresql.conf settings when
building said distribution? AFAIK the minimum default SHHMAX setting on
Red Hat 8.0 is 32MB, seems like bumping shared buffers to work with that
amount would be acceptable inside the 8.0 rpm's.

Yes, this is easy to do. But what is a sane default? I can patch any file
I'd like to, but my preference is to patch as little as possible, as I'm
trying to be generic here. I can't assume Red Hat 8 in the source RPM, and
my binaries are to be preferred only if the distributor doesn't have updated
ones.

[Steve Crawford]

A quick-'n'-dirty first step would be more comments in postgresql.conf. Most
of the lines are commented out which would imply "use the default" but the
default is not shown. (I realize this has the difficulty of defaults that
change depending upon how PostgreSQL was configured/compiled but perhaps
postgresql.conf could be built by the make process based on the configuration
options.)

If postgresql.conf were commented with recommendations it would probably be
all I need though perhaps a recommendation to edit that file should be
displayed at the conclusion of "make install".

Cheers,
Steve

Post by Tom Lane

Post by Merlin Moncure
May I make a suggestion that maybe it is time to start thinking about
tuning the default config file, IMHO its just a little bit too
conservative,

It's a lot too conservative. I've been thinking for awhile that we
should adjust the defaults.
The original motivation for setting shared_buffers = 64 was so that
Postgres would start out-of-the-box on machines where SHMMAX is 1 meg
(64 buffers = 1/2 meg, leaving 1/2 meg for our other shared data
structures). At one time SHMMAX=1M was a pretty common stock kernel
setting. But our other data structures blew past the 1/2 meg mark
some time ago; at default settings the shmem request is now close to
1.5 meg. So people with SHMMAX=1M have already got to twiddle their
postgresql.conf settings, or preferably learn how to increase SHMMAX.
That means there is *no* defensible reason anymore for defaulting to
64 buffers.
We could retarget to try to stay under SHMMAX=4M, which I think is
the next boundary that's significant in terms of real-world platforms
(isn't that the default SHMMAX on some BSDen?). That would allow us
350 or so shared_buffers, which is better, but still not really a
serious choice for production work.
What I would really like to do is set the default shared_buffers to
1000. That would be 8 meg worth of shared buffer space. Coupled with
more-realistic settings for FSM size, we'd probably be talking a shared
memory request approaching 16 meg. This is not enough RAM to bother
any modern machine from a performance standpoint, but there are probably
quite a few platforms out there that would need an increase in their
stock SHMMAX kernel setting before they'd take it.
So what this comes down to is making it harder for people to get
Postgres running for the first time, versus making it more likely that
they'll see decent performance when they do get it running.
It's worth noting that increasing SHMMAX is not nearly as painful as
it was back when these decisions were taken. Most people have moved
to platforms where it doesn't even take a kernel rebuild, and we've
acquired documentation that tells how to do it on all(?) our supported
platforms. So I think it might be okay to expect people to do it.
The alternative approach is to leave the settings where they are, and
to try to put more emphasis in the documentation on the fact that the
factory-default settings produce a toy configuration that you *must*
adjust upward for decent performance. But we've not had a lot of
success spreading that word, I think. With SHMMMAX too small, you
do at least get a pretty specific error message telling you so.
Comments?
regards, tom lane
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[Rod Taylor]

Post by Steve Crawford
A quick-'n'-dirty first step would be more comments in postgresql.conf. Most

This will not solve the issue with the large number of users who have no
interest in looking at the config file -- but are interested in
publishing their results.

[mlw]

Post by Tom Lane

Post by Merlin Moncure
May I make a suggestion that maybe it is time to start thinking about
tuning the default config file, IMHO its just a little bit too
conservative,

It's a lot too conservative. I've been thinking for awhile that we
should adjust the defaults.

One of the things I did on my Windows install was to have a number of
default configuration files, postgresql.conf.small,
postgresql.conf.medium, postgresql.conf.large.

Rather than choose one, in the "initdb" script, ask for or determine the
mount of shared memory, memory, etc.

Another pet peeve I have is forcing the configuration files to be in the
database directory. We had this argument in 7.1 days, and I submitted a
patch that allowed a configuration file to be specified as a command
line parameter. One of the things that Oracle does better is separating
the "configuration" from the data.

It is an easy patch to allow PostgreSQL to use a separate configuration
directory, and specify the data directory within the configuration file
(The way any logical application works), and, NO, symlinks are not a
solution, they are a kludge.

[Jon Griffin]

FYI, my stock linux 2.4.19 gentoo kernel has:
kernel.shmall = 2097152
kernel.shmmax = 33554432

sysctl -a

So it appears that linux at least is way above your 8 meg point, unless I
am missing something.



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[Tom Lane]

Post by Jon Griffin
So it appears that linux at least is way above your 8 meg point, unless I
am missing something.

Yeah, AFAIK all recent Linuxen are well above the range of parameters
that I was suggesting (and even if they weren't, Linux is particularly
easy to change the SHMMAX setting on). It's other Unixoid platforms
that are likely to have a problem. Particularly the ones where you
have to rebuild the kernel to change SHMMAX; people may be afraid to
do that.

Does anyone know whether cygwin has a setting comparable to SHMMAX,
and if so what is its default value? How about the upcoming native
Windows port --- any issues there?

regards, tom lane

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[Matthew T. O'Connor]

Post by Tom Lane

Post by Jon Griffin
So it appears that linux at least is way above your 8 meg point, unless I
am missing something.

Yeah, AFAIK all recent Linuxen are well above the range of parameters
that I was suggesting (and even if they weren't, Linux is particularly
easy to change the SHMMAX setting on). It's other Unixoid platforms
that are likely to have a problem. Particularly the ones where you
have to rebuild the kernel to change SHMMAX; people may be afraid to
do that.

The issue as I see it is:
Better performing vs. More Compatible Out of the box Defaults.

Perhaps a compromise (hack?):
Set the default to some default value that performs well, a value we all
agree is not too big (16M? 32M?). On startup, if the OS can't give us
what we want, instead of failing, we can try again with a smaller
amount, perhaps half the default, if that fails try again with half
until we reach some bottom threshold (1M?).

The argument against this might be: When I set shared_buffers=X, I want
X shared buffers. I don't want it to fail silently and give me less than
what I need / want. To address this we might want to add a guc option
that controls this behavior. So we ship postgresql.conf with 32M of
shared memory and auto_shared_mem_reduction = true. With a comment that
the administrator might want to turn this off for production.

Thoughts?

I think this will allow most uninformed users get decent performing
defaults as most systems will accommodate this larger value.


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[Tom Lane]

... So we ship postgresql.conf with 32M of
shared memory and auto_shared_mem_reduction = true. With a comment that
the administrator might want to turn this off for production.

This really doesn't address Justin's point about clueless benchmarkers,
however. In fact I fear it would make that problem worse: if Joe Blow
says he got horrible performance, who knows whether he was running with
a reasonable number of buffers or not? Especially when you ask him
"did you have lots of shared buffers" and he responds "yes, of course,
it says 32M right here".

We've recently been moving away from the notion that it's okay to
silently lose functionality in order to run on a given system. For
example, if you want to install without readline, you now have to
explicitly tell configure that, because we heard "why don't I have
history in psql" way too often from people who just ran configure
and paid no attention to what it told them.

I think that what this discussion is really leading up to is that we
are going to decide to apply the same principle to performance. The
out-of-the-box settings ought to give reasonable performance, and if
your system can't handle it, you should have to take explicit action
to acknowledge the fact that you aren't going to get reasonable
performance.

regards, tom lane

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[Jeff Hoffmann]

Post by Tom Lane
I think that what this discussion is really leading up to is that we
are going to decide to apply the same principle to performance. The
out-of-the-box settings ought to give reasonable performance, and if
your system can't handle it, you should have to take explicit action
to acknowledge the fact that you aren't going to get reasonable
performance.

What I don't understand is why this is such a huge issue. Set it to a
reasonable level (be it 4M or whatever the concensus is) & let the
packagers worry about it if that's not appropriate. Isn't it their job
to have a good out-of-the-package experience? Won't they have better
knowledge of what the system limits are for the packages they develop
for? Worst case, couldn't they have a standard conf package & a special
"high-performance" conf package in addition to all the base packages?
After all, it's the users of the RPMs that are the real problem, not
usually the people that compile it on their own. If you were having
problems with the "compile-it-yourself" audience, couldn't you just hit
them over the head three or four times (configure, install, initdb &
failed startup to name a few) reminding them to change it if it wasn't
appropriate. What more can you really do? At some point, the end user
has to bear some responsibility...

[Tatsuo Ishii]

It's interesting that people focus on shared_buffers. From my
experience the most dominating parameter for performance is
wal_sync_method. It sometimes makes ~20% performance difference. On
the otherhand, shared_buffers does very little for
performance. Moreover too many shared_buffers cause performance
degration! I guess this is due to the poor design of bufmgr. Until it
is fixed, just increasing the number of shared_buffers a bit, say
1024, is enough IMHO.
--
Tatsuo Ishii

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[Peter Eisentraut]

Post by Tom Lane
We could retarget to try to stay under SHMMAX=4M, which I think is
the next boundary that's significant in terms of real-world platforms
(isn't that the default SHMMAX on some BSDen?). That would allow us
350 or so shared_buffers, which is better, but still not really a
serious choice for production work.

What is a serious choice for production work? And what is the ideal
choice? The answer probably involves some variables, but maybe we should
get values for those variables in each case and work from there.

[Tom Lane]

Post by Peter Eisentraut

Post by Tom Lane
We could retarget to try to stay under SHMMAX=4M, which I think is
the next boundary that's significant in terms of real-world platforms
(isn't that the default SHMMAX on some BSDen?). That would allow us
350 or so shared_buffers, which is better, but still not really a
serious choice for production work.

What is a serious choice for production work?

Well, as I commented later in that mail, I feel that 1000 buffers is
a reasonable choice --- but I have to admit that I have no hard data
to back up that feeling. Perhaps we should take this to the
pgsql-perform list and argue about reasonable choices.

A separate line of investigation is "what is the lowest common
denominator nowadays?" I think we've established that SHMMAX=1M
is obsolete, but what replaces it as the next LCD? 4M seems to be
correct for some BSD flavors, and I can confirm that that's the
current default for Mac OS X --- any other comments?

regards, tom lane

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[Christopher Kings-Lynne]

Post by Tom Lane

Post by Peter Eisentraut

Post by Tom Lane
We could retarget to try to stay under SHMMAX=4M, which I think is
the next boundary that's significant in terms of real-world platforms
(isn't that the default SHMMAX on some BSDen?). That would allow us
350 or so shared_buffers, which is better, but still not really a
serious choice for production work.

What is a serious choice for production work?

Well, as I commented later in that mail, I feel that 1000 buffers is
a reasonable choice --- but I have to admit that I have no hard data
to back up that feeling. Perhaps we should take this to the
pgsql-perform list and argue about reasonable choices.

Damn. Another list I have to subscribe to!

The results I just posted indicate that 1000 buffers is really quite bad
performance comaped to 4000, perhaps up to 100 TPS for selects and 30 TPS
for TPC-B.

Still, that 1000 is in itself vastly better than 64!!

Chris



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[Christopher Kings-Lynne]

Post by Tom Lane
A separate line of investigation is "what is the lowest common
denominator nowadays?" I think we've established that SHMMAX=1M
is obsolete, but what replaces it as the next LCD? 4M seems to be
correct for some BSD flavors, and I can confirm that that's the
current default for Mac OS X --- any other comments?

It's 1025 * 4k pages on FreeBSD = 4MB

Chris


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[Peter Eisentraut]

Post by Tom Lane
Well, as I commented later in that mail, I feel that 1000 buffers is
a reasonable choice --- but I have to admit that I have no hard data
to back up that feeling.

I know you like it in that range, and 4 or 8 MB of buffers by default
should not be a problem. But personally I think if the optimal buffer
size does not depend on both the physical RAM you want to dedicate to
PostgreSQL and the nature and size of the database, then we have achieved
a medium revolution in computer science. ;-)

[Tom Lane]

Post by Peter Eisentraut
I know you like it in that range, and 4 or 8 MB of buffers by default
should not be a problem. But personally I think if the optimal buffer
size does not depend on both the physical RAM you want to dedicate to
PostgreSQL and the nature and size of the database, then we have achieved
a medium revolution in computer science. ;-)

But this is not about "optimal" settings. This is about "pretty good"
settings. As long as we can get past the knee of the performance curve,
I think we've done what should be expected of a default parameter set.

I believe that 1000 buffers is enough to get past the knee in most
scenarios. Again, I haven't got hard evidence, but that's my best
guess.

regards, tom lane

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[Bruce Momjian]

Post by Peter Eisentraut

Post by Tom Lane
Well, as I commented later in that mail, I feel that 1000 buffers is
a reasonable choice --- but I have to admit that I have no hard data
to back up that feeling.

I know you like it in that range, and 4 or 8 MB of buffers by default
should not be a problem. But personally I think if the optimal buffer
size does not depend on both the physical RAM you want to dedicate to
PostgreSQL and the nature and size of the database, then we have achieved
a medium revolution in computer science. ;-)

I have thought about this and I have an idea. Basically, increasing the
default values may get us closer, but it will discourage some to tweek,
and it will cause problems with some OS's that have small SysV params.

So, my idea is to add a message at the end of initdb that states people
should run the pgtune script before running a production server.

The pgtune script will basically allow us to query the user, test the OS
version and perhaps parameters, and modify postgresql.conf with
reasonable values. I think this is the only way to cleanly get folks
close to where they should be.

For example, we can ask them how many rows and tables they will be
changing, on average, between VACUUM runs. That will allow us set the
FSM params. We can ask them about using 25% of their RAM for shared
buffers. If they have other major apps running on the server or have
small tables, we can make no changes. We can basically ask them
questions and use that info to set values.

We can even ask about sort usage maybe and set sort memory. We can even
control checkpoint_segments this way if they say they will have high
database write activity and don't worry about disk space usage. We may
even be able to compute some random page cost estimate.

Seems a script is going to be the best way to test values and assist
folks in making reasonable decisions about each parameter. Of course,
they can still edit the file, and we can ask them if they want
assistance to set each parameter or leave it alone.

I would restrict the script to only deal with tuning values, and tell
people they still need to review that file for other useful parameters.

Another option would be to make a big checklist or web page that asks
such questions and computes proper values, but it seems a script would
be easiest. We can even support '?' which would explain why the
question is being ask and how it affects the value.

[Daniel Kalchev]

[...]

Post by Bruce Momjian
For example, we can ask them how many rows and tables they will be
changing, on average, between VACUUM runs. That will allow us set the
FSM params. We can ask them about using 25% of their RAM for shared
buffers. If they have other major apps running on the server or have
small tables, we can make no changes. We can basically ask them
questions and use that info to set values.

Bruce, this is an very good idea and such tool would simplify setup for the
me-too type of DBA - we should definitely try to attract them.

However, how could one possibly answer the above question, if they setup their
database for the first time?

What is more, these settings are on a per-installation, not per-database -
which means, that if you have several small, but active databases and one
large database the requirements will be very different.

Nobody likes answering such questions when installing new software. You might
enjoy it the first few times, but then learn the 'answers' and don't even
think what the question is. (we all know the answer :)

Perhaps indeed a better idea is to have PostgreSQL itself collect usage
statistics, and from time to time print 'suggestions' to the log file (best in
my opinion), or have these available via some query. These suggestions should
best reflect the of course require minimal intervention to the database
system, such as restart etc.


Daniel



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[Bruce Momjian]

I imagined they could run pgtune anytime after install to update those
performance parameters. It gives them a one-stop location to at least
do minimal tuning, and as their load changes, they can run it again.

---------------------------------------------------------------------------

Post by Daniel Kalchev
[...]

Post by Bruce Momjian
For example, we can ask them how many rows and tables they will be
changing, on average, between VACUUM runs. That will allow us set the
FSM params. We can ask them about using 25% of their RAM for shared
buffers. If they have other major apps running on the server or have
small tables, we can make no changes. We can basically ask them
questions and use that info to set values.

Bruce, this is an very good idea and such tool would simplify setup for the
me-too type of DBA - we should definitely try to attract them.
However, how could one possibly answer the above question, if they setup their
database for the first time?
What is more, these settings are on a per-installation, not per-database -
which means, that if you have several small, but active databases and one
large database the requirements will be very different.
Nobody likes answering such questions when installing new software. You might
enjoy it the first few times, but then learn the 'answers' and don't even
think what the question is. (we all know the answer :)
Perhaps indeed a better idea is to have PostgreSQL itself collect usage
statistics, and from time to time print 'suggestions' to the log file (best in
my opinion), or have these available via some query. These suggestions should
best reflect the of course require minimal intervention to the database
system, such as restart etc.
Daniel
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[Jason Hihn]

Pardon my ignorance, but there's no way to auto-tune? Ship it with a thread
that gathers statistics and periodically re-tunes the database parameters.
Of course, be able to turn it off. People that actually take the time to run
tune manually will turn it off as to not have the overhead or interruption.
Those that don't care about pg_tune shouldn't care about having a thread
around retuning. Those that will care will tune manually.



-----Original Message-----
From: pgsql-advocacy-***@postgresql.org
[mailto:pgsql-advocacy-***@postgresql.org]On Behalf Of Bruce Momjian
Sent: Thursday, February 13, 2003 2:22 PM
To: Daniel Kalchev
Cc: PostgresSQL Hackers Mailing List; pgsql-***@postgresql.org
Subject: Re: [pgsql-advocacy] [HACKERS] Changing the default
configuration



I imagined they could run pgtune anytime after install to update those
performance parameters. It gives them a one-stop location to at least
do minimal tuning, and as their load changes, they can run it again.

---------------------------------------------------------------------------

Post by Daniel Kalchev
[...]

Post by Bruce Momjian
For example, we can ask them how many rows and tables they will be
changing, on average, between VACUUM runs. That will allow us set the
FSM params. We can ask them about using 25% of their RAM for shared
buffers. If they have other major apps running on the server or have
small tables, we can make no changes. We can basically ask them
questions and use that info to set values.

Bruce, this is an very good idea and such tool would simplify setup for the
me-too type of DBA - we should definitely try to attract them.
However, how could one possibly answer the above question, if they setup their
database for the first time?
What is more, these settings are on a per-installation, not per-database -
which means, that if you have several small, but active databases and one
large database the requirements will be very different.
Nobody likes answering such questions when installing new software. You might
enjoy it the first few times, but then learn the 'answers' and don't even
think what the question is. (we all know the answer :)
Perhaps indeed a better idea is to have PostgreSQL itself collect usage
statistics, and from time to time print 'suggestions' to the log file (best in
my opinion), or have these available via some query. These suggestions should
best reflect the of course require minimal intervention to the database
system, such as restart etc.
Daniel
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--
Bruce Momjian | http://candle.pha.pa.us
***@candle.pha.pa.us | [phone]
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073

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[Bruce Momjian]

To auto-tune, you would need to monitor swap usage and other stuff that
may vary too much based on load from other systems. Only the admin
knows how to answer some of those questions.

---------------------------------------------------------------------------

Post by Jason Hihn
Pardon my ignorance, but there's no way to auto-tune? Ship it with a thread
that gathers statistics and periodically re-tunes the database parameters.
Of course, be able to turn it off. People that actually take the time to run
tune manually will turn it off as to not have the overhead or interruption.
Those that don't care about pg_tune shouldn't care about having a thread
around retuning. Those that will care will tune manually.
-----Original Message-----
Sent: Thursday, February 13, 2003 2:22 PM
To: Daniel Kalchev
Subject: Re: [pgsql-advocacy] [HACKERS] Changing the default
configuration
I imagined they could run pgtune anytime after install to update those
performance parameters. It gives them a one-stop location to at least
do minimal tuning, and as their load changes, they can run it again.
---------------------------------------------------------------------------

Post by Daniel Kalchev
[...]

Post by Bruce Momjian
For example, we can ask them how many rows and tables they will be
changing, on average, between VACUUM runs. That will allow us set the
FSM params. We can ask them about using 25% of their RAM for shared
buffers. If they have other major apps running on the server or have
small tables, we can make no changes. We can basically ask them
questions and use that info to set values.

Bruce, this is an very good idea and such tool would simplify setup for

the

Post by Daniel Kalchev
me-too type of DBA - we should definitely try to attract them.
However, how could one possibly answer the above question, if they setup

their

Post by Daniel Kalchev
database for the first time?
What is more, these settings are on a per-installation, not per-database -
which means, that if you have several small, but active databases and one
large database the requirements will be very different.
Nobody likes answering such questions when installing new software. You

might

Post by Daniel Kalchev
enjoy it the first few times, but then learn the 'answers' and don't even
think what the question is. (we all know the answer :)
Perhaps indeed a better idea is to have PostgreSQL itself collect usage
statistics, and from time to time print 'suggestions' to the log file

(best in

Post by Daniel Kalchev
my opinion), or have these available via some query. These suggestions

should

Post by Daniel Kalchev
best reflect the of course require minimal intervention to the database
system, such as restart etc.
Daniel
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--
Bruce Momjian | http://candle.pha.pa.us
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
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[Josh Berkus]

HEY PEOPLE!

How about we take this discussion to the Performance List, where it belongs?

[Daniel Kalchev]

Post by Josh Berkus
How about we take this discussion to the Performance List, where it belongs?

I believe the design and addition of code that collects and outputs the usage patterns of the database (statistics) belongs here.

If we take the approach to providing information to tune PostgreSQL based on real-world usage, I guess we need at least the following:

- Usage statistics on a per-database or even per-table level. I believe we already collect some;
- Statistics analysis tool/routine/process to produce suggestions;
- Of course lots of real-world data to justify the suggestions;

- Can we provide more knobs for tunable parameters that can be applied on a per-database or even per-table level. One first candidate might be the FSM?
- Can some of these parameters (when available) to auto-tune?

Of course, this could move out of pgsql-hackers :)

Daniel


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[Daniel Kalchev]

Post by Jason Hihn
Pardon my ignorance, but there's no way to auto-tune? Ship it with a thread
that gathers statistics and periodically re-tunes the database parameters.
Of course, be able to turn it off. People that actually take the time to run
tune manually will turn it off as to not have the overhead or interruption.
Those that don't care about pg_tune shouldn't care about having a thread
around retuning. Those that will care will tune manually.

This is related to my proposition, but trouble is, there is not such thing as
'well tuned database' that will suit all queries. You can tune the database to
the hardware for example (still remember that old argument on random access
and fast disks).

It seems the system could 'self-tune' itself on minor choices. I believe it
does this today for a number of things already. More significant changes
require the DBA consent and choice - but they need to be well informed of the
current usage statistics when making the choice.

Daniel


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[Daniel Kalchev]

Post by Bruce Momjian
I imagined they could run pgtune anytime after install to update those
performance parameters. It gives them a one-stop location to at least
do minimal tuning, and as their load changes, they can run it again.

True, but to make reasonably good choice, they will need to base the parameter
selection on some statistics data. Not many people do trough testing before
tuning their system and in many cases, the tests one do rarely resemble the
real-world usage of their database(s).

I agree that pgtune would be wonderful tool in this case, but they first need
to get some idea what parameters should be given to it.

This process if further complicated by the fact that we can tune PostgreSQL on
a per-installation basis, instead of on per-database basis - many of the
parameters, for example FSM and sort memory are database related. We usually
split data into databases to put related data together or data with similar
usage pattern etc.

Daniel


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[Tom Lane]

Post by Bruce Momjian
So, my idea is to add a message at the end of initdb that states people
should run the pgtune script before running a production server.

Do people read what initdb has to say?

IIRC, the RPM install scripts hide initdb's output from the user
entirely. I wouldn't put much faith in such a message as having any
real effect on people...

regards, tom lane

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[Bruce Momjian]

Post by Tom Lane

Post by Bruce Momjian
So, my idea is to add a message at the end of initdb that states people
should run the pgtune script before running a production server.

Do people read what initdb has to say?
IIRC, the RPM install scripts hide initdb's output from the user
entirely. I wouldn't put much faith in such a message as having any
real effect on people...

Yes, that is a problem. We could show something in the server logs if
pg_tune hasn't been run. Not sure what else we can do, but it would
give folks a one-stop thing to run to deal with performance
configuration.

We could prevent the postmaster from starting unless they run pg_tune or
if they have modified postgresql.conf from the default. Of course,
that's pretty drastic.

[Kevin Brown]

Post by Bruce Momjian
We could prevent the postmaster from starting unless they run pg_tune or
if they have modified postgresql.conf from the default. Of course,
that's pretty drastic.

If you're going to do that, then you may as well make the defaults
something that will perform reasonably well under the widest
circumstances possible and let the postmaster fail when it can't
acquire the resources those defaults demand.

What I'd do is go ahead and make the defaults something reasonable,
and if the postmaster can't allocate, say, enough shared memory pages,
then it should issue an error message saying not only that it wasn't
able to allocate enough shared memory, but also which parameter to
change and (if it's not too much trouble to implement) what it can be
changed to in order to get past that part of the initialization (this
means that the postmaster has to figure out how much shared memory it
can actually allocate, via a binary search allocate/free method). It
should also warn that by lowering the value, the resulting performance
may be much less than satisfactory, and that the alternative (to
increase SHMMAX, in this example) should be used if good performance
is desired.

That way, someone whose only concern is to make it work will be able
to do so without having to do a lot of experimentation, and will get
plenty of warning that the result isn't likely to work very well.

And we end up getting better benchmarks in the cases where people
don't have to touch the default config. :-)

[Curt Sampson]

Post by Tom Lane
It's a lot too conservative. I've been thinking for awhile that we
should adjust the defaults.

Some of these issues could be made to Just Go Away with some code
changes. For example, using mmap rather than SysV shared memory
would automatically optimize your memory usage, and get rid of the
double-buffering problem as well. If we could find a way to avoid using
semephores proportional to the number of connections we have, then you
wouldn't have to worry about that configuration parameter, either.

In fact, some of this stuff might well improve our portability, too.
For example, mmap is a POSIX standard, whereas shmget is only an X/Open
standard. That makes me suspect that mmap is more widely available on
non-Unix platforms. (But I could be wrong.)

cjs

[scott.marlowe]

Post by Curt Sampson

Post by Tom Lane
It's a lot too conservative. I've been thinking for awhile that we
should adjust the defaults.

Some of these issues could be made to Just Go Away with some code
changes. For example, using mmap rather than SysV shared memory
would automatically optimize your memory usage, and get rid of the
double-buffering problem as well. If we could find a way to avoid using
semephores proportional to the number of connections we have, then you
wouldn't have to worry about that configuration parameter, either.
In fact, some of this stuff might well improve our portability, too.
For example, mmap is a POSIX standard, whereas shmget is only an X/Open
standard. That makes me suspect that mmap is more widely available on
non-Unix platforms. (But I could be wrong.)

I'll vote for mmap. I use the mm libs with apache/openldap/authldap and
it is very fast and pretty common nowadays. It seems quite stable as
well.


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[Christopher Kings-Lynne]

Why don't we include a postgresql.conf.recommended along with our
postgresql.conf.sample. That shouldn't be too hard. We can just jack up
the shared buffers and wal buffers and everything - it doesn't matter if
it's not perfect, but it will at least give people an idea of what needs to
be increased, etc to get good results.

I'm currently benchmarking our new DB server before we put it into
production. I plan to publish the results from that shortly.

Regards,

Chris

-----Original Message-----
Sent: Tuesday, 11 February 2003 11:44 PM
To: Greg Copeland
Subject: Re: [pgsql-advocacy] [HACKERS] PostgreSQL Benchmarks
I've tested all the win32 versions of postgres I can get my hands on
(cygwin and not), and my general feeling is that they have problems with
insert performance with fsync() turned on, probably the fault of the os.
Select performance is not so much affected.
This is easily solved with transactions and other such things. Also
Postgres benefits from pl just like oracle.
May I make a suggestion that maybe it is time to start thinking about
tuning the default config file, IMHO its just a little bit too
conservative, and its hurting you in benchmarks being run by idiots, but
its still bad publicity. Any real database admin would know his test
are synthetic and not meaningful without having to look at the #s.
This is irritating me so much that I am going to put together a
benchmark of my own, a real world one, on (publicly available) real
world data. Mysql is a real dog in a lot of situations. The FCC
publishes a database of wireless transmitters that has tables with 10
million records in it. I'll pump that into pg, run some benchmarks,
real world queries, and we'll see who the faster database *really* is.
This is just a publicity issue, that's all. Its still annoying though.
I'll even run an open challenge to database admin to beat query
performance of postgres in such datasets, complex multi table joins,
etc. I'll even throw out the whole table locking issue and analyze
single user performance.
Merlin
_____________
How much of the performance difference is from the RDBMS, from the
middleware, and from the quality of implementation in the middleware.
While I'm not surprised that the the cygwin version of PostgreSQL is
slow, those results don't tell me anything about the quality of the
middleware interface between PHP and PostgreSQL. Does anyone know if we
can rule out some of the performance loss by pinning it to bad
middleware implementation for PostgreSQL?
Regards,
--
Copeland Computer Consulting
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[Merlin Moncure]

True, but even so, 32 max connections is a bit light. I have more
pgsql databases than that on my box now. My point in my previous answer

to Tom was that you HAVE to shut down postgresql to change this. It
doesn't allocate tons of semaphores on startup,
[snip]

is this correct? I recall looking through the source and seeing
comments to the affect that it is better to allocate them all
(semaphores) up front in order to prevent runtime failed allocations.
(could be totally off base on this).

You don't have to be using apache to need more than 32 simo connections.

Heck, how many postgresql databases do you figure are in production with

that setting still in there? My guess is not many.

[snip]
True, and it is not unheard of to put minimum specs for version x of the
database, i.e. 7.4 requires kernel 2.x and so on.

Here's the comment I was referring to:

/*
* InitProcGlobal -
* initializes the global process table. We put it here so that
* the postmaster can do this initialization.
*
* We also create all the per-process semaphores we will need to
support
* the requested number of backends. We used to allocate
semaphores
* only when backends were actually started up, but that is bad
because
* it lets Postgres fail under load --- a lot of Unix systems are
* (mis)configured with small limits on the number of semaphores,
and
* running out when trying to start another backend is a common
failure.
* So, now we grab enough semaphores to support the desired max
number
* of backends immediately at initialization --- if the sysadmin
has set
* MaxBackends higher than his kernel will support, he'll find
out sooner
* rather than later.
*
* Another reason for creating semaphores here is that the
semaphore
* implementation typically requires us to create semaphores in
the
* postmaster, not in backends.
*/

Merlin

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[scott.marlowe]

Post by Merlin Moncure
/*
* InitProcGlobal -
* initializes the global process table. We put it here so that
* the postmaster can do this initialization.
*
* We also create all the per-process semaphores we will need to
support
* the requested number of backends. We used to allocate
semaphores
* only when backends were actually started up, but that is bad
because
* it lets Postgres fail under load --- a lot of Unix systems are
* (mis)configured with small limits on the number of semaphores,
and
* running out when trying to start another backend is a common
failure.
* So, now we grab enough semaphores to support the desired max
number
* of backends immediately at initialization --- if the sysadmin
has set
* MaxBackends higher than his kernel will support, he'll find
out sooner
* rather than later.
*
* Another reason for creating semaphores here is that the
semaphore
* implementation typically requires us to create semaphores in
the
* postmaster, not in backends.
*/

Interesting. I was looking at the max number of file handles, but not
semaphores. I don't have to adjust the sem settings until I break 2047
connections, about 10 times what I want to set the default to.

With max connections set to 200 and buffers set to 1000, I pretty much
can't run out of system resources on my box, only postgresql resources.

My box running RH72 has about 6500 free file handles out of the default
8192 left when running 200 simo transactions with pgbench, and the 200 max
connects setting would account for about 10% of the shared semaphore max
on the box, well under what I'd worry about.

So, what OSes would have a problem, if any, with boosting something
like max connects to 200? What are the breaking points on other OSes?

I just downloaded FreeBSD 5.0 yesterday, so I'll try to get it installed
and tested as well.



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[Andrew Sullivan]

Post by scott.marlowe
So, what OSes would have a problem, if any, with boosting something
like max connects to 200? What are the breaking points on other OSes?

Solaris 8 broke at 200, the last time I tried on a new box. 150
didn't break it, though.

Given the absolute bare-minimum hardware you can get Solaris to work
on, Solaris installs with totally silly defaults for all this stuff.
I dunno why they do it that way, but anyway, anyone using Solaris
_will_ need to reconfigure the kernel (just for the default config),
so problems there aren't an argument for leaving the defaults alone.

A
--
----
Andrew Sullivan 204-4141 Yonge Street
Liberty RMS Toronto, Ontario Canada
<***@libertyrms.info> M2P 2A8
[phone] x110


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[Dann Corbit]

-----Original Message-----
Sent: Tuesday, February 11, 2003 10:32 PM
To: Shridhar
Subject: Re: [pgsql-advocacy] [HACKERS] PostgreSQL Benchmarks
There's "The Open Source Database Benchmark",
http://osdb.sourceforge.net/.
Anyone tried to use it?

Requires a real Linux or UNIX installation. Won't run under Cygwin. At
least I could not get it to work. Got it compiled, but I am missing
something to make it work correctly.

Here are some other benchmark things:
http://www.eweek.com/article2/0,3959,293,00.asp
Which has this link:
ftp://ftp.eweek.com/pub/eweek/pdf/printpub/benchmark/dbbenchmark_v1.zip

This article:
http://www.dcc.unicamp.br/~celio/mc527/interbase/PCweek_test.html
Has this code:
ftp://ftp.zdnet.com/pcweek/labs/0207codefile.zip
But it requires the very expensive "Benchmark Factory" product. It
might be useful to people who already have "benchmark factory".

Another open source database test:
http://sourceforge.net/projects/osdldbt


Java database benchmark routines:
http://www.firstsql.com/firstsqlj/


This site:
http://www.mipt.sw.ru/
(which does not appear to be available right now)
Has three excellent benchmark tools, ATS, LTS, OTS.
They are Windows machine centric, though, and would probably be very
hard to port to Unix environments.

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[Dann Corbit]

A financial database benchmark:
http://www.cs.nyu.edu/cs/faculty/shasha/fintime.html

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[Dann Corbit]

This is how to get the FIPS benchmark. It measures CONFORMANCE rather
than performance:
http://www.itl.nist.gov/div897/ctg/sql_form.htm

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[Dann Corbit]

The benchmark handbook:
http://www.benchmarkresources.com/handbook/contents.asp

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[Kevin Brown]

Post by Christopher Kings-Lynne
Hrm. I just saw that the PHP ADODB guy just published a bunch of database
benchmarks. It's fairly evident to me that benchmarking PostgreSQL on
http://php.weblogs.com/oracle_mysql_performance
*sigh*

Not fair, perhaps.

But if you look, you'll see that *Cygwin* PostgreSQL beat most
everything on the Win32 platform except MySQL and Oracle with PL/SQL.
Read further and you'll see that Cygwin PostgreSQL came *really* close
(within 10% or something) to MS-SQL.

Considering that they weren't even running a native version of
PostgreSQL, I think the results were surprisingly *good*.


But yes, we really do want to be the fastest. :-)