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Date: Fri, 14 Dec 2012 13:50:25 -0500
From: "Kevin Grittner" <kgrittn@mail.com>
Message-ID: <20121214185025.80080@gmx.com>
MIME-Version: 1.0
Subject: Re: PostgreSQL Performance Tuning / Postgresql.conf and on OS
 Level
To: "Shams Khan" <shams.khan22@gmail.com>,pgsql-admin@postgresql.org
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Sender: pgsql-admin-owner@postgresql.org

Shams Khan wrote:

> *Need to increase the response time of running queries on
> server...*

> 8 CPU's and 16 cores

> [64GB RAM]

> HDD 200GB
> Database size = 40GB

Without more info, there's a bit of guesswork, but...

> maintenance_work_mem = Not initialised

I would say probably 1GB

> effective_cache_size = Not initialised

48GB

> work_mem = Not initialised

You could probably go 100MB on this.

> wal_buffers = 8MB

16BM

> checkpoint_segments = 16

Higher. Probably not more than 128.

> shared_buffers = 32MB (have read should 20% of Physical memory)

16GB to start. If you have episodes of high latency, where even
queries which normally run very quickly all pause and then all
complete close together after a delay, you may need to reduce this
and/or increase the aggressiveness of the background writer. I've
had to go as low as 1GB to overcome such latency spikes.

> max_connections = 100

Maybe leave alone, possibly reduce. You should be aiming to use a
pool to keep about 20 database connections busy. If you can't do
that in the app, look at pgbouncer.

>  checkpoint_completion_target = Not initialised

It is often wise to increase this to 0.8 or 0.9

If I read this right, you have one 200GB drive for writes? That's
going to be your bottleneck if you write much data. You need a RAID
for both performance and reliability, with a good controller with
battery-backed cache configured for write-back. Until you have one
you can be less crippled on preformance by setting
synchronous_commit = off. The trade-off is that there will be a
slight delay between when PostgreSQL acknoleges a commit and when
the data is actually persisted.

-Kevin


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