On Thu, Dec 13, 2012 at 3:03 PM, Andres Freund <andres@2ndquadrant.com> wrote: > It moves a computation of the sort of: > > result -= vacuum_defer_cleanup_age; > if (!TransactionIdIsNormal(result)) > result = FirstNormalTransactionId; > > inside ProcArrayLock. But I can't really imagine that to be relevant...
I can. Go look at some of the 9.2 optimizations around GetSnapshotData(). Those made a BIG difference under heavy concurrency and they were definitely micro-optimization. For example, the introduction of NormalTransactionIdPrecedes() was shockingly effective.
The two commits coming to my mind are: - ed0b409 (Separate PGPROC into PGPROC and PGXACT) - 0d76b60 (introduction of NormalTransactionIdPrecedes) Those ones really improved concurrency performance.