On Sun, May 12, 2013 at 3:46 PM, Jim Nasby <jim@nasby.net> wrote:
> On 5/10/13 1:06 PM, Jeff Janes wrote:
>>
>> Of course the paranoid DBA could turn off restart_after_crash and do a
>> manual investigation on every crash, but in that case the database would
>> refuse to restart even in the case where it perfectly clear that all the
>> following WAL belongs to the recycled file and not the current file.
>
>
> Perhaps we should also allow for zeroing out WAL files before reuse (or just
> disable reuse). I know there's a performance hit there, but the reuse idea
> happened before we had bgWriter. Theoretically the overhead creating a new
> file would always fall to bgWriter and therefore not be a big deal.
For filesystems like btrfs, re-using a WAL file is suboptimal to
simply creating a new one and removing the old one when it's no longer
required. Using fallocate (or posix_fallocate) (I have a patch for
that!) to create a new one is - by my tests - 28 times faster than the
currently-used method.
--
Jon