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Re: How to force Nested Loop plan?

From: Rob Nagler <nagler(at)bivio(dot)biz>
To: PgSQL Performance ML <pgsql-performance(at)postgresql(dot)org>
Subject: Re: How to force Nested Loop plan?
Date: 2003-08-30 23:59:33
Message-ID: 16209.14949.507000.384083@gargle.gargle.HOWL (view raw or flat)
Thread:
Lists: pgsql-performance
Ron Johnson writes:
> Dumb question: given your out-of-the-box satisfaction, could it be
> that postgresql.conf hasn't been tweaked?

Here are the modified values:

shared_buffers = 8000
wal_buffers = 80
sort_mem = 32000
effective_cache_size = 400000
random_page_cost = 4
autocommit = false
timezone = UTC

I had run a test with effective_cache_size to high value to see what
would happen.  Also adjusted random_page_cost:

random_page_cost effective_cache_size	elbow
    4	    	    	40000	    	675
    .5	    	    	40000	    	592
    .1	    	    	40000	    	392
    4	    	    	1000	    	30

My conclusion is that random_page_cost should be left alone and
effective_cache_size higher is better.

BTW, the hardware is 2 x 2.4ghz Xeon, 1.2GB, SCSI (linux software
raid) with 10K disks.  This is close to the production box.  Although
we are planning on adding more memory to production.

Rob



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