Re: kernel version impact on PostgreSQL performance

Cyril Scetbon wrote:
> Does anyone know what can be the differences between linux kernels
> 2.6.29 and 2.6.30 that can cause this big difference (TPS x 7 !)
> http://www.phoronix.com/scan.php?page=article&item=linux_2624_2633&num=2

Discussed in detail at
http://archives.postgresql.org/message-id/4B512D0D.4030909@2ndquadrant.com

You might need the background information at
http://developer.postgresql.org/pgdocs/postgres/wal-reliability.html to
be able to follow what that's talking about.

The short version is that ext3 combined with regular hard drives has
never been safe for database use by default, it was cheating on writes
in a way that left it possible for corruption to occur after a crash.
The change in ext4 that caused the performance drop is from the kernel
developers finally eliminating the source for that cheat.  The result
should be reliable operation by default, which unfortunately happens to
be much slower operation by default too.

--
Greg Smith  2ndQuadrant US  Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com   www.2ndQuadrant.us