Re: First-draft release notes for next week's releases

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