BUG #10748: xmax is not resetting properly with FOR UPDATE

From: pinker(at)onet(dot)eu
To: pgsql-bugs(at)postgresql(dot)org
Subject: BUG #10748: xmax is not resetting properly with FOR UPDATE
Date: 2014-06-24 14:29:26
Message-ID: 20140624142926.2618.16610@wrigleys.postgresql.org
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The following bug has been logged on the website:

Bug reference: 10748
Logged by: Alicja Kucharczyk
Email address: pinker(at)onet(dot)eu
PostgreSQL version: 9.3.4
Operating system: RedHat
Description:

The problem is described here:
http://stackoverflow.com/questions/24382158/strange-cleanup-behaviour-with-for-update

The main problem is that xmax values stays set with xid of transaction that
has already committed. The documentation says: "The identity (transaction
ID) of the deleting transaction, or zero for an undeleted row version. It is
possible for this column to be nonzero in a visible row version. That
usually indicates that the deleting transaction hasn't committed yet, or
that an attempted deletion was rolled back."

I have used this feature for a queue to avoid locking, but it doesn't work
together with FOR UPDATE clause.

best regards,
A.Kucharczyk

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