Re: RE: [COMMITTERS] pgsql/src/backend/access/transam ( xact.c xlog.c)

* Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> [001111 12:06] wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> >> I have to agree with Alfred here: this does not sound like a feature,
> >> it sounds like a horrid hack. You're giving up *all* consistency
> >> guarantees for a performance gain that is really going to be pretty
> >> minimal in the WAL context.
>
> > It does not give up consistency. The db is still consistent, it is just
> > consistent from a few seconds ago, rather than commit time.
>
> No, it isn't consistent. Without the fsync you don't know what order
> the kernel will choose to plop down WAL log blocks in; you could end up
> with a corrupt log. (Actually, perhaps that could be worked around if
> the log blocks are suitably marked so that you can tell where the last
> sequentially valid one is. I haven't looked at the log structure in
> any detail...)

This could be fixed by using O_FSYNC on the open call for the WAL
data files on *BSD, i'm not sure of the sysV equivelant, but I know
it exists.

--
-Alfred Perlstein - [bright(at)wintelcom(dot)net|alfred(at)freebsd(dot)org]
"I have the heart of a child; I keep it in a jar on my desk."