Re: limiting hint bit I/O

On Tue, Jan 18, 2011 at 12:44 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Tue, Jan 18, 2011 at 9:24 AM, Merlin Moncure <mmoncure@gmail.com> wrote:
>> a few weeks back I hacked an experimental patch that removed the hint
>> bit action completely.  the results were very premature and/or
>> incorrect, but my initial findings suggested that hint bits might not
>> be worth the cost from performance standpoint.  i'd like to see some
>> more investigation in this direction before going with a complex
>> application mechanism (although that would be beneficial vs the status
>> quo).
>
> I think it's not very responsible to allege that hint bits aren't
> providing a benefit without providing the patch that you used and the
> tests that you ran.  This is a topic that needs careful analysis, and
> I think that saying "hint bits don't provide a benefit... maybe..."
> doesn't do anything but confuse the issue.  How about doing some tests
> with the patch from my OP and posting the results?  If removing hint
> bits entirely doesn't degrade performance, then surely the
> less-drastic approach I've taken here ought to be OK too.  But in my
> testing, it didn't look too good.

hm. well, I would have to agree on the performance hit -- I figure 5%
scan penalty should be about the maximum you'd want to pay to get the
i/o reduction.  Odds are you're correct and I blew something...I'd be
happy to test your patch.

merlin