Re: Read only transactions - Commit or Rollback - Mailing list pgsql-performance

From Tom Lane
Subject Re: Read only transactions - Commit or Rollback
Date
Msg-id 125.1135095412@sss.pgh.pa.us
Whole thread Raw
In response to Re: Read only transactions - Commit or Rollback  (Greg Stark <gsstark@mit.edu>)
List pgsql-performance
Greg Stark <gsstark@mit.edu> writes:
> Tom Lane <tgl@sss.pgh.pa.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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