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Possible Bug?

From: Francis Reader <freader(at)imerge(dot)co(dot)uk>
To: "'pgsql-bugs(at)postgresql(dot)org'" <pgsql-bugs(at)postgresql(dot)org>
Subject: Possible Bug?
Date: 2002-07-08 13:13:28
Message-ID: C0D45ABB3F45D5118BBC00508BC292DBA943EF@imgserv04 (view raw or flat)
Thread:
Lists: pgsql-bugs
We are running pg 7.1.3. x86 Redhat 6.1 with 2.4.17 and glibc 2.2.2.

We have several s/w subsystems which keep some pg backends open for a VERY
period of time. (Well the whole time the machine is powered up.), and others
which have a short lifetime when connected to pg backends.

The total amount of data stored within the database is relatively small <
30Mb.

We have seen occurences when pg runs out of disk space (currently it has
approx 90Mb allocated to it) and fails.

In some circumstances we have noticed that some backends still have file
descriptors open to /pg_xlog/0000* files even though they have obviously
been deleted some while ago when that wal file was no longer referenced.

Is this expected behaviour? Or just an artifact that the backend life is
prolonged in our use of pg.

We have started experimenting with wal_files and checkpoint_segment settings
to see how that affects both the number of wal file created and whether or
not they get deleted correctly. 

At the time of writing, even with wal_files =1 and checkpoint_segment =1 pg
appeared to have one current wal file and one which had been deleted and
still referenced by a backend. (You can observer these by "ls -l
/proc/*/fd/* | grep xlog" )

eg:
lrwx------   1 postgres postgres       64 Apr 22 21:20 /proc/1576/fd/36 
-> /db/live/pg_xlog/0000000000000002 (deleted)
lrwx------   1 postgres postgres       64 Apr 22 21:20 /proc/1613/fd/36 
-> /db/live/pg_xlog/0000000000000000 (deleted)
lrwx------   1 postgres postgres       64 Apr 22 21:20 /proc/1672/fd/36 
-> /db/live/pg_xlog/0000000000000000 (deleted)
lrwx------   1 postgres postgres       64 Apr 22 21:20 /proc/1763/fd/36 
-> /db/live/pg_xlog/0000000000000000 (deleted)
lrwx------   1 postgres postgres       64 Apr 22 21:20 /proc/1803/fd/26 
-> /db/live/pg_xlog/0000000000000000 (deleted)
lrwx------   1 postgres postgres       64 Apr 22 21:20 /proc/3241/fd/36 
-> /db/live/pg_xlog/0000000000000000 (deleted)


TIA 

Francis Reader



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