Looking at the way cache invalidations are handled in two-phase transactions, it would be simpler if we store the shared cache invalidation messages in the twophase state file header, like we store deleted relations and subxids. This allows them to be copied to the COMMIT_PREPARED WAL record, so that we don't need treat twophase commits differently than regular ones in xact_redo_commit. As the patch stands, the new xactGetCommittedInvalidationMessages/MakeSharedInvalidMessagesArray mechanism is duplicated functionality with AtPrepare_Inval/-PersistInvalidationMessage - both materialize the pending shared invalidation messages so that they can be written to disk. I did that in my git branch.
I wonder if we might have alignment issues with the SharedInvalidationMessages being stored in WAL records, following the subxids. All the data stored in that record have 4-byte alignment at the moment, but if SharedInvalidationMessage ever needs 8-byte alignment, we would have trouble. Probably not worth changing code, it's highly unlikely that SharedInvalidationMessage will ever need 8-byte alignment, but perhaps a comment somewhere would be in order. I note that we don't emit RunningXacts after a shutdown checkpoint. So if recovery starts at a shutdown checkpoint, we don't let read-only backends in until the first online checkpoint. Could we treat a shutdown checkpoint as a snapshot with no transactions running? Or do prepared transactions screw that up? -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
