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Re: cheaper snapshots redux

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Markus Wanner <markus(at)bluegap(dot)ch>, Jim Nasby <jim(at)nasby(dot)net>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: cheaper snapshots redux
Date: 2011-08-25 14:59:37
Message-ID: 2294.1314284377@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> Well, one long-running transaction that only has a single XID is not
> really a problem: the snapshot is still small.  But one very old
> transaction that also happens to have a large number of
> subtransactions all of which have XIDs assigned might be a good way to
> stress the system.

That's a good point.  If the ring buffer size creates a constraint on
the maximum number of sub-XIDs per transaction, you're going to need a
fallback path of some sort.

			regards, tom lane

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