Re: Losing data

In response to Garry Saddington <garry(at)schoolteachers(dot)co(dot)uk>:

> On Thursday 19 June 2008 16:55, Joshua D. Drake wrote:
> > On Thu, 2008-06-19 at 16:55 +0100, Garry Saddington wrote:
> > > I have had a serious loss of data and wondered if anyone could shed any
> > > light on what may have happened.
> > > My users have been writing reports on students. No error messages have
> > > been produced and when called back up the reports seem to be present at
> > > the time of writing. However, next day they have disappeared, and they do
> > > not appear in a pg_dump. They seem to have been kept in memory and never
> > > written to disk.
> > > We are using Zope and connecting to Postgres through psycopg on Centos 5.
> > > I suspect a hard disk failure but any other ideas would be welcome.
> > > Would these reports be in the WAL?
> >
> > If it was hardware related you would know, quickly. This sounds a great
> > deal more like an application level interaction. Perhaps your zope
> > application caches things for a while before committing to disk?
> Yes I thought of this but once the report is sent to the DB a separate query
> is run to get all of that teacher's reports and these are then displayed on a
> new page. They all appear here but then disappear later. Zope has transaction
> machinery that rolls everything back on an error, so Postgres must have
> indicated a successful write somehow. I read in a Postgres manual that the
> hard disk may report to the OS that a write has occured when it actually has
> not, is this possible?

No. If that happens you end up with corrupt disks. The chance of that
going unnoticed by the OS is pretty slim.

> Oh, and the problem has been intermittant. Another
> thing that happened this morning is that Postgres had today as 18/06/2008
> when in fact it was 19/06/2008 and the OS reported this correctly. Restarting
> postgres sorted it, could this be the problem?

Sounds to me like there's something seriously wrong with you OS or your
PostgreSQL install. What version of PostgreSQL is this? What OS?

--
Bill Moran
Collaborative Fusion Inc.
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wmoran(at)collaborativefusion(dot)com
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