| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | Simon Riggs <simon(at)2ndQuadrant(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Reduce WAL logging of INSERT SELECT |
| Date: | 2011-08-06 17:43:53 |
| Message-ID: | 1312652633.10087.13.camel@jdavis |
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| Lists: | pgsql-hackers |
On Fri, 2011-08-05 at 23:16 -0400, Bruce Momjian wrote:
> Well, if the table is created in the same transaction (which is the only
> case under consideration), no other sessions can write to the table so
> you are just writing the entire table on commit, rather than to the WAL.
The transaction can still write to many tables that way, and that could
mean many fsyncs.
Also, there may be a bunch of other transactions trying to write to the
WAL that have to wait as your transaction has to seek out to fsync the
data file and then seek back to the WAL.
Regards,
Jeff Davis
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