Re: Simplifying wal_sync_method

Magnus Hagander wrote:
> > > > Now thinking about it, the guy had corrupt table, not WAL log.
> > > > How is WAL->tables synched? Does the 'wal_sync_method'
> > > > affect it or not?
> > >
> > > I *think* it always fsyncs() there as it is now, but I'm
> > not 100% sure.
> >
> > wal_sync_method is also used to flush pages during a
> > checkpoint, so it could lead to table corruption too, not
> > just WAL corruption.
> >
> > However, on Unix, 99% of corruption is caused by bad disk or RAM.
>
> ... or iDE disks with write cache enabled. I've certainly seen more than
> what I'd call 1% (though I haven't studied it to be sure) that's because
> of write-cached disks...

Personally, I can't remember a case that was caused by something other
than bad RAM or bad disk.

Let me write up a section in the manual on this for 8.1, and link it to
the wal_sync_method documentation section, and see how it looks. Even
re-ordering the items in the docs and making bullets has made it clearer
to me what is happening, and what is the default.

--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073