Re: Losing data

-------------- Original message ----------------------
From: 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? 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?
> Regards
> Garry
>

Seems like a transaction with no commit. Basically along as the session is active the data is there but once the session is closed the data does not persist.

--
Adrian Klaver
aklaver(at)comcast(dot)net