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Re: Read only transactions - Commit or Rollback

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Greg Stark <gsstark(at)mit(dot)edu>
Cc: Markus Schaber <schabi(at)logix-tt(dot)com>, PostgreSQL Performance List <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Read only transactions - Commit or Rollback
Date: 2005-12-20 16:16:52
Message-ID: 125.1135095412@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Greg Stark <gsstark(at)mit(dot)edu> writes:
> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>> That surprises me too --- can you provide details on the test case so
>> other people can reproduce it?  AFAIR the only performance difference
>> between SERIALIZABLE and READ COMMITTED is the frequency with which
>> transaction status snapshots are taken; your report suggests you were
>> spending 30% of the time in GetSnapshotData, which is a lot higher than
>> I've ever seen in a profile.

> Perhaps it reduced the amount of i/o concurrent vacuums were doing?

Can't see how it would do that.

			regards, tom lane

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