Alvaro Herrera wrote:
Tom Lane wrote:
Gregory Stark <[EMAIL PROTECTED]> writes:
Is there a reason UnpinBuffer has to be the one to increment the usage count
anyways? Why can't ReadBuffer handle incrementing the count and just trust
that it won't be decremented until the buffer is unpinned anyways?
That's a good question.  I think the idea was that if we hold a buffer
pinned for awhile (long enough that the bgwriter's clock sweep passes
over it one or more times), we want the usage count decrementing to
start when we release the pin, not when we acquire it.  But maybe that
could be fixed if the clock sweep doesn't touch the usage_count of a
pinned buffer.  Which in fact it may not do already --- didn't look.

It does -- in BgBufferSync the "all" scan calls SyncOneBuffer with
skip_pinned=false.  The "lru" scan does skip pinned buffers.

You're looking at the wrong place. StrategyGetBuffer drives the clock sweep, and it always decreases the usage_count, IOW it doesn't skip pinned buffers. SyncOneBuffer and BgBufferSync don't decrease the usage_count in any case.

  Heikki Linnakangas

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