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Re: Losing data

From: Garry Saddington <garry(at)schoolteachers(dot)co(dot)uk>
To: pgsql-general(at)postgresql(dot)org
Subject: Re: Losing data
Date: 2008-06-19 16:38:53
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Lists: pgsql-general
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?

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