Re: patch to allow disable of WAL recycling

On 26.06.18 15:35, Jerry Jelinek wrote:
> Attached is a patch to provide an option to disable WAL recycling. We
> have found that this can help performance by eliminating
> read-modify-write behavior on old WAL files that are no longer resident
> in the filesystem cache. The is a lot more detail on the background of
> the motivation for this in the following thread.

Your patch describes this feature as a performance feature. We would
need to see more measurements about what this would do on other
platforms and file systems than your particular one. Also, we need to
be careful with user options that trade off reliability for performance
and describe them in much more detail.

If the problem is specifically the file system caching behavior, then we
could also consider using the dreaded posix_fadvise().

Then again, I can understand that turning off WAL recycling is sensible
on ZFS, since there is no point in preallocating space that will never
be used. But then we should also turn off all other preallocation of
WAL files, including the creation of new (non-recycled) ones.

--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services