Thread: VX_CONCURRENT flag on vxfs( 5.1 or later) for performance for postgresql?

Dear all

When database files are on a VxFS filesystem, performance can be
significantly improved by setting the VX_CONCURRENT cache advisory on
the file according to vxfs document,

my question is that have any tested by this?


#include <sys/fs/vx_ioctl.h>
ioctl(fd, VX_SETCACHE, VX_CONCURRENT);


Regards

HSIEN WEN

On 04/27/2011 11:33 PM, HSIEN-WEN CHU wrote:
> When database files are on a VxFS filesystem, performance can be
> significantly improved by setting the VX_CONCURRENT cache advisory on
> the file according to vxfs document,
>

That won't improve performance, and it's not safe either.  VX_CONCURRENT
switches the filesystem to use direct I/O.  That's usually slower for
PostgreSQL.  And it introduces some requirements for both block
alignment and the application avoiding overlapping writes.  PostgreSQL
doesn't do either, so I wouldn't expect it to be compatible with
VX_CONCURRENT.

--
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us