Did this ever get addressed? ---------------------------------------------------------------------------
Simon Riggs wrote: > > As part of a performance investigation for a customer I've noticed an > O(N^2) performance issue on COMMITs of transactions that contain many > SAVEPOINTs. I've consistently measured COMMIT times of around 9 seconds, > with 49% CPU, mostly in LockReassignCurrentOwner(). > > BEGIN; > INSERT... > SAVEPOINT ... > INSERT... > SAVEPOINT ... > ... (repeat 10,000 times) > COMMIT; > > The way SAVEPOINTs work is that each is nested within the previous one, > so that at COMMIT time we must recursively commit all the > subtransactions before we issue final commit. > > That's a shame because ResourceOwnerReleaseInternal() contains an > optimisation to speed up final commit, by calling ProcReleaseLocks(). > > What we actually do is recursively call LockReassignCurrentOwner() which > sequentially scans LockMethodLocalHash at each level of transaction. The > comments refer to this as "retail" rather than the wholesale method, > which never gets to execute anything worthwhile in this case. > > This issue does NOT occur in PLpgSQL functions that contain many > EXCEPTION clauses in a loop, since in that case the subtransactions are > started and committed from the top level so that the subxact nesting > never goes too deep. > > Fix looks like we need special handling for the depth-first case, rather > than just a recursion loop in CommitTransactionCommand(). > > Issues looks like it goes all the way back, no fix for 9.0. > > I notice also that the nesting model of SAVEPOINTs also means that > read-only subtransactions will still generate an xid when followed by a > DML statement. That's unnecessary, but required given current design. > > -- > Simon Riggs www.2ndQuadrant.com > PostgreSQL Development, 24x7 Support, Training and Services > > > -- > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-hackers -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers