| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
| Cc: | Csaba Nagy <nagy(at)ecircle-ag(dot)com>, postgres hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: CLUSTER and MVCC |
| Date: | 2007-03-09 16:36:29 |
| Message-ID: | 420.1173458189@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
> We wouldn't clean up tuples that are visible to a transaction, but if
> you have one long-running transaction like pg_dump in a database with
> otherwise short transaction, you'll have a lot of tuples that are not
> vacuumable because of the long-running process, but are not in fact
> visible to any transaction.
It sounds to me like you are proposing to remove the middles of update
chains, which would break READ-COMMITTED updates initiated by the older
transactions. Now admittedly pg_dump isn't going to issue any such
updates, but VACUUM doesn't know that.
regards, tom lane
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