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. -- Michael
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