On Thu, 5 Apr 2007, John Allgood wrote:
The hard thing about running multiple postmasters is that you have to tune
each one separate. Most of the databases I have limited the max-connections
to 30-50 depending on the database. What would reasonable values for
effective_cache_size and random_page_cost. I think I have these default.
Also what about kernel buffers on RHEL4.
Normally, you would look at the output of 'free' and set it to the amount of
cache/8. For example:
total used free shared buffers cached
Mem: 2055120 2025632 29488 0 505168 368132
-/+ buffers/cache: 1152332 902788
Swap: 2048184 2380 2045804
So, you could take 902788/8 = 112848. This machine is a bad example as it's
just a workstation, but you get the idea.
That tells the planner it can expect the OS cache to have that much of the DB
cached. It's kind of an order of magnitude knob, so it doesn't have to be
that precise.
Since you're running multiple postmasters on the same machine (5 per machine
right?), then setting the shared_buffers up to 50000 (400MB) on each
postmaster is probably desirable, though if you have smaller DBs on some of
them, it might only be worth it for the largest one. I suspect that having
the effective_cache_size set to the output of free on each postmaster is
desirable, but your case likely requires some benchmarking to find the optimal
config.
If you look through the archives, there is a formula for calculating what you
need to set the kernel shared memory parameters. Otherwise, you can just
start postgres and look at the log as it'll tell you what it tried to
allocate.
Hopefully there's someone with experience running multiple postmasters on the
same machine that can speak to the postgresql.conf knobs more specifically.
I'd still suggest you upgrade to at least 8.1.8.
Thanks
-----Original Message-----
From: pgsql-performance-owner@xxxxxxxxxxxxxx
[mailto:pgsql-performance-owner@xxxxxxxxxxxxxx] On Behalf Of Jeff Frost
Sent: Thursday, April 05, 2007 3:24 PM
To: John Allgood
Cc: pgsql-performance@xxxxxxxxxxxxxx
Subject: Re: [PERFORM] High Load on Postgres 7.4.16 Server
On Thu, 5 Apr 2007, John Allgood wrote:
Hello All
I sent this message to the admin list and it never got through so I
am trying the performance list.
We moved our application to a new machine last night. It is a Dell
PowerEdge 6950 2X Dual Core. AMD Opteron 8214 2.2Ghz. 8GB Memory. The
machine is running Redhat AS 4 Upd 4 and Redhat Cluster Suite. The SAN is
an
EMC SAS connected via fibre. We are using Postgres 7.4.16. We have
recently
had some major hardware issues and replaced the hardware with brand new
Dell
equipment. We expected a major performance increase over the previous
being
the old equipment was nearly three years old
I will try and explain how things are configured. We have 10
separate postmasters running 5 on each node. Each of the postmasters is a
single instance of each database. Each database is separated by division
and
also we have them separate so we can restart an postmaster with needing to
restart all databases My largest database is about 7 GB. And the others
run
anywhere from 100MB - 1.8GB.
The other configuration was RHEL3 and Postgres 7.4.13 and Redhat
Cluster Suite. The application seemed to run much faster on the older
equipment.
My thoughts on the issues are that I could be something with the OS
tuning. Here is what my kernel.shmmax, kernel.shmall = 1073741824. Is
there
something else that I could tune in the OS. My max_connections=35 and
shared
buffers=8192 for my largest database.
John,
Was the SAN connected to the previous machine or is it also a new addition
with the Dell hardware? We had a fairly recent post regarding a similar
upgrade in which the SAN ended up being the problem, so the first thing I
would do is test the SAN with bonnie-++ and/or move your application to use
a
local disk and test again. With 8GB of RAM, I'd probably set the
shared_buffers to at least 50000...If I remember correctly, this was the
most
you could set it to on 7.4.x and continue benefitting from it. I'd strongly
encourage you to upgrade to at least 8.1.8 (and possibly 8.2.3) if you can,
as
it has much better shared memory management. You might also want to double
check your effective_cache_size and random_page_cost to see if they are set
to
reasonable values. Did you just copy the old postgresql.conf over?
This is the beginning of the thread I mentioned above:
http://archives.postgresql.org/pgsql-performance/2007-03/msg00104.php
--
Jeff Frost, Owner <jeff@xxxxxxxxxxxxxxxxxxxxxx>
Frost Consulting, LLC http://www.frostconsultingllc.com/
Phone: 650-780-7908 FAX: 650-649-1954
