Heikki Linnakangas <[EMAIL PROTECTED]> writes: > One idea is to keep track which pins are taken using the bulk strategy. > It's a bit tricky when a buffer is pinned multiple times since we don't > know which ReleaseBuffer corresponds which ReadBuffer, but perhaps we > could get away with just a flag per pinned buffer. Set the flag when a > buffer is pinned with bulk strategy and it wasn't pinned by us before, > and clear it when it's pinned with another strategy. I'm thinking we > steal one bit from PrivateRefCount for this.
Seems like a mess. Why don't we just fix it so there's no need for different behavior at Unpin time? The facts on the ground are that the current patch's change in UnpinBuffer is a no-op anyway, because of the tupletableslot interference. The behavior I'm imagining is just that when we try to take a buffer from the ring, if its usage count exceeds 1 then drop it from the ring and get another buffer. 1 would be the expected case if no one had touched it since we last used it. >> A heapscan would pin the buffer only once and hence bump its count at >> most once, so I don't see a big problem here. Also, I'd argue that >> buffers that had a positive usage_count shouldn't get sucked into the >> ring to begin with. > True, except that with the synchronized scans patch two synchronized > scans will pin the buffer twice. Hmm. But we probably don't want the same buffer in two different backends' rings, either. You *sure* the sync-scan patch has no interaction with this one? One other question: I see the patch sets the threshold for switching from normal to ring-buffer heapscans at table size = NBuffers. Why so high? I'd have expected maybe at most NBuffers/4 or NBuffers/10. If you don't want a seqscan blowing out your buffer cache, you surely don't want it blowing out 90% of the cache either. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match