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Re: Recovering a database in danger of transaction wrap-around

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Steven Rosenstein <srosenst(at)us(dot)ibm(dot)com>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: Recovering a database in danger of transaction wrap-around
Date: 2008-01-25 19:10:06
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-admin
Steven Rosenstein <srosenst(at)us(dot)ibm(dot)com> writes:
> I did as instructed, and fired up the standalone backend.  I then started
> VACUUM.  About four days later, the standalone backend terminated with the
> message:

> WARNING:  terminating connection because of crash of another server process
> DETAIL:  The postmaster has commanded this server process to roll back the
> current transaction and exit, because another server process exited
> abnormally and possibly corrupted shared memory.
> HINT:  In a moment you should be able to reconnect to the database and
> repeat your command.
> CONTEXT:  writing block 465 of relation 1663/16384/863912

Ugh.  Something sent the standalone backend a SIGQUIT signal.  You need
to find out what did that.

> I used lsof to monitor which files the backend was actually working on.  It
> took two of the four days for it to vacuum a single table with 43
> one-gigabyte extents.  I have one table with over 300 extents.  I'm looking
> at a vacuum process which can ultimately take weeks (if not months) to
> complete.

Yipes.  You are just using plain VACUUM, right, not VACUUM FULL?
Have you checked that vacuum_cost_delay isn't enabled?

> Bottom line.  Is there *any* way of faking out the 1 million transaction
> limit which prevents the postmaster from running, long enough for me to use
> pg_dump to rescue the data?

In 8.1 those limits are all hard-wired; you'd need to modify
SetTransactionIdLimit() in src/backend/access/transam/varsup.c
and recompile.  Might be worth doing, if you think these tables
have been bloated by a complete lack of vacuuming.

			regards, tom lane

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Subject: Re: Recovering a database in danger of transaction wrap-around
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