From: | Merlin Moncure <mmoncure(at)gmail(dot)com> |
---|---|
To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Jim Nasby <jim(at)nasby(dot)net>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, Josh Berkus <josh(at)agliodbs(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: limiting hint bit I/O |
Date: | 2011-01-19 12:57:12 |
Message-ID: | AANLkTimR9Bv7BQL6zc7KeXaGo-y9Kp26DA-+tdUnhMhC@mail.gmail.com |
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Lists: | pgsql-hackers |
On Tue, Jan 18, 2011 at 12:44 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Tue, Jan 18, 2011 at 9:24 AM, Merlin Moncure <mmoncure(at)gmail(dot)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
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