Re: PQExec returns null question

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Donald Carlile <carlile@me.com>
Cc: pgsql-interfaces@postgresql.org
Subject: Re: PQExec returns null question
Date: Mon, 20 Oct 2014 13:31:08 -0400
Message-ID: <2666.1413826268@sss.pgh.pa.us> (raw)
In-Reply-To: <D2BB3EEC-5FA7-4EB3-B232-ADBBC06590B0@me.com>
References: <D2BB3EEC-5FA7-4EB3-B232-ADBBC06590B0@me.com>
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Donald Carlile <carlile@me.com> writes:
> Our OS X application uses PostgreSQL as a back end through pqlib. Some of our customers are reporting occasional PGRES_FATAL_ERRORs, but PQresultErrorMessage returns a blank string. I have looked at the sources, and as far as I can tell, this condition can only occur when PQExec returns a null. The docs say that this shouldnt happen except in out of memory conditions. I am not using any Copy actions.
> I have two broad questions. 1) What can I do to prevent this from happening? 2) If it does happen, how can I remedy it?

There's a recent bug report
http://www.postgresql.org/message-id/20141019003736.2662.84048@wrigleys.postgresql.org
suggesting that this might happen after a loss of connection.  It'd be a
libpq bug that it's not providing a more useful error message in such a
case, but probably the more interesting question from your standpoint
is why is the server dropping the connection.  Have you looked into the
postmaster log to see if anything gets logged when this happens?

If it's not a connection-loss case then you've found some new bug that
we ought to look into, but without a reproducible test case it's hard
to do much in that line.

			regards, tom lane

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