On Thu, 2009-05-14 at 13:28 -0400, Tom Lane wrote: > Simon Riggs <si...@2ndquadrant.com> writes: > > In a thread on -perform it has been observed that our Read-Only > > scalability is not as good as it could be. One problem being that we > > need to scan the whole of the ProcArray to derive a snapshot, which > > becomes the dominant task with many users. > > GetSnapshotData doesn't take an exclusive lock. Neither does start or > end of a read-only transaction. AFAIK there is no reason, and certainly > no shred of experimental evidence, to think that ProcArrayLock > contention is the bottleneck for read-only scenarios.
I agree completely; I didn't mention the ProcArrayLock at all... I did mention scanning the procarray itself, which is likely too big to fit in on-chip cache and so must be re-read from main RAM each time. -- Simon Riggs www.2ndQuadrant.com PostgreSQL Training, Services and Support -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
