Re: Clock sweep not caching enough B-Tree leaf pages?

On Thu, Apr 17, 2014 at 5:00 PM, Greg Stark <stark(at)mit(dot)edu> wrote:
> On Thu, Apr 17, 2014 at 10:18 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> Because all the usage counts are the same, the eviction at
>> this point is completely indiscriminate. We're just as likely to kick
>> out a btree root page or a visibility map page as we are to kick out a
>> random heap page, even though the former have probably been accessed
>> several orders of magnitude more often. That's clearly bad.
>
> That's not clear at all. In that circumstance regardless of what page
> you evict you're incurring precisely one page fault i/o when the page
> is read back in.

I am a bit confused by this remark. In *any* circumstance when you
evict you're incurring precisely one page fault I/O when the page is
read back in. That doesn't mean that the choice of which page to
evict is irrelevant.

--
Robert Haas
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