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Re: Commitfest patches

From: Martijn van Oosterhout <kleptog(at)svana(dot)org>
To: Gregory Stark <stark(at)enterprisedb(dot)com>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>,Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Commitfest patches
Date: 2008-03-28 18:48:47
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Lists: pgsql-hackers
On Fri, Mar 28, 2008 at 05:34:30PM +0000, Gregory Stark wrote:
> But what I really need is someone to read the patch and say "looks good" or
> point out things they don't like. In particular, what I really, really want is
> some guidance on the singular key question I asked.

I was going to write all sorts of stuff, till I noticed Heikki said
basically everything I was going to say:

- I think normal index scans could benefit from this (it was measurable
when I was playing with AIO in postgres a few years back).
- The integration with the bitmap scan is good, neat even
- I think the number of preread_count is far too small, given you get a
benefit even if you only have one spindle.
- I don't understand the ramp-up method either.

People spend a lot of time worrying about hundreds of posix_fadvise()
calls but you don't need anywhere near that much to be effective. With
AIO I limited the number of outstanding requests to a dozen and it was
still useful. You lose nothing by capping the number of requests at any

> I want to know if we're interested in the more invasive patch restructuring
> the buffer manager. My feeling is that we probably are eventually. But I
> wonder if people wouldn't feel more comfortable taking baby steps at first
> which will have less impact in cases where it's not being heavily used.

I think the way it is now is neat and simple and enough for now.

Have a nice day,
Martijn van Oosterhout   <kleptog(at)svana(dot)org>
> Please line up in a tree and maintain the heap invariant while 
> boarding. Thank you for flying nlogn airlines.

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