| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Martijn van Oosterhout <kleptog(at)svana(dot)org> |
| Cc: | Gregory Wood <gregw(at)com-stock(dot)com>, PostgreSQL-General <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: Is vacuum full lock like old's vacuum's lock? |
| Date: | 2002-03-09 00:24:45 |
| Message-ID: | 26850.1015633485@sss.pgh.pa.us |
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| Lists: | pgsql-general |
Martijn van Oosterhout <kleptog(at)svana(dot)org> writes:
> Actually, it seems to me you could get this to play with MVCC by treating
> the move as a UPDATE that does nothing. Copy the tuple from the end to the
> beginning, mark the end one as deleted and the beginning one as new. Voila,
> tuple moved and everything will eventually use the new one and ignore the
> old one.
... except for scans in progress ...
VACUUM FULL is indeed like an UPDATE as far as crash recovery goes:
either the original tuple or the moved one is good, never both. The
problem is to ensure that concurrent scans will see the tuple correctly.
regards, tom lane
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