| From: | Hannu Krosing <hannu(at)skype(dot)net> |
|---|---|
| To: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
| Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, nagy(at)ecircle-ag(dot)com |
| Subject: | Re: CLUSTER and MVCC |
| Date: | 2007-03-09 12:25:35 |
| Message-ID: | 1173443135.3132.5.camel@localhost.localdomain |
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| Thread: | |
| Lists: | pgsql-hackers |
Ühel kenal päeval, R, 2007-03-09 kell 11:29, kirjutas Heikki
Linnakangas:
> Is there a particular reason why CLUSTER isn't MVCC-safe? It seems to me
> that it would be trivial to fix, by using SnapshotAny instead of
> SnapshotNow, and not overwriting the xmin/xmax with the xid of the
> cluster command.
>
> I feel that I must missing something, or someone would've already fixed
> it a long time ago...
Probably it is not MVCC safe because the relation is swapped out from
under the pg_class.
That is, it can be possible , that older and newer transactions read
different datafiles and so simle MVCC does not work.
> Csaba, you mentioned recently
> (http://archives.postgresql.org/pgsql-hackers/2007-03/msg00027.php) that
> you're actually using the MVCC-violation to clean up tables during a
> backup. Can you tell us a bit more about that? Would you be upset if we
> shut that backdoor?
>
> In any case, the MVCC-violation needs to be documented. I'll send a doc
> patch to pgsql-patches shortly.
>
--
----------------
Hannu Krosing
Database Architect
Skype Technologies OÜ
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