Re: XID wraparound and busy databases

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: XID wraparound and busy databases
Date: 2007-08-15 16:49:52
Message-ID: 7058.1187196592@sss.pgh.pa.us
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Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
> Maybe we can do something to reduce the xid consumption? For example,
> reuse xids for read-only queries.

Hmm, that's an idea.

More simply, just keep the current transaction open (resetting
everything but the XID) if we have made no changes by the time we're
told to commit or rollback ... which is something we track already,
so as not to waste cycles on useless commit XLOG records.

You'd want some upper limit on transaction lifetime, so as to avoid the
"long lived transactions hurt VACUUM" problem, but even reusing a single
xact for a few seconds would pretty much eliminate this issue, I bet.
It's hard to see how anyone could be doing 6K xacts/sec unless most are
read-only.

regards, tom lane

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