From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
---|---|
To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
Cc: | Greg Stark <stark(at)mit(dot)edu>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Josh Berkus <josh(at)agliodbs(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: First-draft release notes for next week's releases |
Date: | 2014-03-17 23:51:31 |
Message-ID: | 20140317235130.GQ6899@eldon.alvh.no-ip.org |
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Lists: | pgsql-hackers |
Andres Freund wrote:
> On 2014-03-17 21:09:10 +0000, Greg Stark wrote:
> > That said, it would be nice to actually fix the problem, not just
> > detect it. Eventually vacuum would fix the problem. I think. I'm not
> > really sure what will happen actually.
>
> Indexes will quite possibly stay corrupted. I think. If there was a
> index lookup for a affected row, the kill_prior_tuple logic will have
> quite possibly have zapped the index entry.
>
> Aside from that, it looks like VACUUM will have a hard time cleaning up
> as well. It looks to me like heap_prune_chain() won't remove tuples that
> are marked as both HeapTupleHeaderIsHeapOnly() and
> HeapTupleHeaderIsHotUpdated(), i.e. intermediate tuples in a HOT
> chain. Neither will lazy_scan_heap()...
Ugh :-(
> I think the best way to really cleanup a table is to use something like:
> ALTER TABLE rew ALTER COLUMN data TYPE text USING (data);
> where text is the previous type of the column. That should trigger a
> full table rewrite, without any finesse about tracking ctid chains.
Isn't this what VACUUM FULL does?
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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