From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Greg Stark <stark(at)mit(dot)edu> |
Cc: | 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 23:39:19 |
Message-ID: | 20140317233919.GS16438@awork2.anarazel.de |
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Thread: | |
Lists: | pgsql-hackers |
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()...
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.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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