Re: old synchronized scan patch

Gregory Stark <stark@enterprisedb.com> writes:
> "Tom Lane" <tgl@sss.pgh.pa.us> writes:
>> Sure, it should hang around for awhile, and will.  The problem is that
>> its lifetime will be artificially inflated, so that the seqscan ends up
>> kicking out other blocks that are really of greater importance, rather
>> than recycling its own old blocks as it should.

> I thought you had switched this all to a clock sweep algorithm.

Yeah ... it's a clock sweep with counter.  A buffer's counter is
incremented by each access and decremented when the sweep passes over
it.  So multiple accesses allow the buffer to survive longer.  For a
large seqscan you really would rather the counter stayed at zero,
because you want the buffers to be recycled when the sweep comes back
the first time.
        regards, tom lane