Re: RE: xlog checkpoint depends on sync() ... seems uns afe

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> "Mikheev, Vadim" <vmikheev(at)SECTORBASE(dot)COM> writes:
> >> The idea is, that by the time the last sync has run, the
> >> first sync will be done flushing the buffers to disk. - this is what
> >> we were told by the IBM engineers when I worked tier-2/3 AIX support
> >> at IBM.
>
> > I was told the same a long ago about FreeBSD. How much can we count on
> > this undocumented sync() feature?
>
> Sounds quite unreliable to me. Unless there's some interlock ... like,
> say, the second sync not being able to advance past a buffer page that's
> as yet unwritten by the first sync. But would all Unixen share such a
> strange detail of implementation?

I'm pretty sure it has no basis in fact, it's just one of these habits
that gives sysadmins a warm fuzzy feeling. ;) It's apparently been
around a long time, though I don't remember where I read about it--it
was quite a few years ago.

-Doug