Horton

Re: heap vacuum & cleanup locks

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2011-11-10T02:10:25Z
Lists: pgsql-hackers

Commits

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  1. Make VACUUM avoid waiting for a cleanup lock, where possible.

On Wed, Nov 9, 2011 at 6:10 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
> On Wed, Nov 9, 2011 at 10:20 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Simon Riggs <simon@2ndQuadrant.com> writes:
>>> heapgetpage() gets a page and a pin, but holds the pin until it reads
>>> the next page. Wow!
>>
>>> That is both annoying and very dumb. It should hold the pin long
>>> enough to copy the data and then release the pin.
>>
>> I don't find that anywhere near as obvious as you seem to.  I think you
>> are trying to optimize for the wrong set of conditions.
>
> ISTM we should optimise to access the cachelines in the buffer once.
> Holding a pin and re-accessing the buffer via main memory seems pretty
> bad plan to me. Which conditions are being optimised by doing that?

I believe it reduces memory copying.  But we can certainly test some
alternative you may have in mind and see how it shakes out.

-- 
Robert Haas
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