On Mon, Sep 25, 2017 at 10:17 AM, Alexander Kuzmenkov <a.kuzmen...@postgrespro.ru> wrote: > Here is some news about the CSN patch. > > * I merged it with master (58bd60995f), which now has the clog group update. > With this optimization, CSN is now faster than the master by about 15% on > 100 to 400 clients (72 cores, pgbench tpcb-like, scale 500). It does not > degrade faster than master as it did before. The numbers of clients greater > than 400 were not measured.
Hmm, that's gratifying. > * Querying for CSN of subtransactions was not implemented in the previous > version of the patch, so I added it. I tested the performance on the > tpcb-like pgbench script with some savepoints added, and it was > significantly worse than on the master. The main culprit seems to be the > ProcArrayLock taken in GetSnapshotData, GetRecentGlobalXmin, > ProcArrayEndTransaction. Although it is only taken in shared mode, just > reading the current lock mode and writing the same value back takes about > 10% CPU. Maybe we could do away with some of these locks, but there is some > interplay with imported snapshots and replication slots which I don't > understand well. I plan to investigate this next. That's not so good, though. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
