On Wednesday, October 03, 2012 10:12:58 PM Michael Paquier wrote: > On 2012/10/03, at 23:52, Andres Freund <[email protected]> wrote: > > On Wednesday, October 03, 2012 04:28:59 PM Tom Lane wrote: > >> Andres Freund <[email protected]> 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 ;) I think that might result in deadlocks with concurrent sessions in some circumstances if those other sessions already have a lower level lock on the index. Thats why I think dropping the lock on the index and then reacquiring an access exlusive might be necessary. Its not a too likely scenario, but why not do it right if its just 3 lines...
Andres -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list ([email protected]) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
