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Re: Support for REINDEX CONCURRENTLY

From: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
To: Andres Freund <andres(at)2ndquadrant(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Greg Stark <stark(at)mit(dot)edu>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Support for REINDEX CONCURRENTLY
Date: 2012-10-03 20:12:58
Message-ID: E8867ECA-6804-446B-AFAE-24D2C6E8BCDD@gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On 2012/10/03, at 23:52, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:

> On Wednesday, October 03, 2012 04:28:59 PM Tom Lane wrote:
>> Andres Freund <andres(at)2ndquadrant(dot)com> writes:
>>> Maybe I am missing something here, but reindex concurrently should do
>>> 1) BEGIN
>>> 2) Lock table in share update exlusive
>>> 3) lock old index
>>> 3) create new index
>>> 4) obtain session locks on table, old index, new index
>>> 5) commit
>>> 6) process till newindex->insisready (no new locks)
>>> 7) process till newindex->indisvalid (no new locks)
>>> 8) process till !oldindex->indisvalid (no new locks)
>>> 9) process till !oldindex->indisready (no new locks)
>>> 10) drop all session locks
>>> 11) lock old index exlusively which should be "invisible" now
>>> 12) drop old index
>> 
>> You can't drop the session locks until you're done.  Consider somebody
>> else trying to do a DROP TABLE between steps 10 and 11, for instance.
> Yea, the session lock on the table itself probably shouldn't be dropped. If 
> were holding only that one there shouldn't be any additional deadlock dangers 
> when dropping the index due to lock upgrades as were doing the normal dance 
> any DROP INDEX does. They seem pretty unlikely in a !valid !ready table 
> 
Just à note...
My patch drops the locks on parent table and indexes at the end of process, after dropping the old indexes ;)

Michael
> 
> Greetings,
> 
> Andres
> -- 
> Andres Freund        http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Training & Services


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