Simon Riggs <simon@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.
regards, tom lane