On 2013-09-26 20:40:40 +0900, Michael Paquier wrote: > On Thu, Sep 26, 2013 at 7:34 PM, Andres Freund <and...@2ndquadrant.com> wrote: > > On 2013-09-26 12:13:30 +0900, Michael Paquier wrote: > >> > 2) I don't think the drop algorithm used now is correct. Your > >> > index_concurrent_set_dead() sets both indisvalid = false and indislive = > >> > false at the same time. It does so after doing a WaitForVirtualLocks() - > >> > but that's not sufficient. Between waiting and setting indisvalid = > >> > false another transaction could start which then would start using that > >> > index. Which will not get updated anymore by other concurrent backends > >> > because of inislive = false. > >> > You really need to follow index_drop's lead here and first unset > >> > indisvalid then wait till nobody can use the index for querying anymore > >> > and only then unset indislive. > > > >> Sorry, I do not follow you here. index_concurrent_set_dead calls > >> index_set_state_flags that sets indislive and *indisready* to false, > >> not indisvalid. The concurrent index never uses indisvalid = true so > >> it can never be called by another backend for a read query. The drop > >> algorithm is made to be consistent with DROP INDEX CONCURRENTLY btw. > > > > That makes it even worse... You can do the concurrent drop only in the > > following steps: > > 1) set indisvalid = false, no future relcache lookups will have it as valid
> indisvalid is never set to true for the concurrent index. Swap is done > with concurrent index having indisvalid = false and former index with > indisvalid = true. The concurrent index is validated with > index_validate in a transaction before swap transaction. Yes. I've described how it *has* to be done, not how it's done. The current method of going straight to isready = false for the original index will result in wrong results because it's not updated anymore while it's still being used. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers