From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
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To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: heap vacuum & cleanup locks |
Date: | 2011-11-08 15:08:53 |
Message-ID: | CA+U5nMJ-tFgrLnFV0Q24c-4Co58erkPemyvHG_vJcA69CTHbwg@mail.gmail.com |
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Lists: | pgsql-hackers |
On Tue, Nov 8, 2011 at 1:50 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> But there's an efficiency argument against doing it that way. First,
> if we release the pin then we'll have to reacquire the buffer, which
> means taking and releasing a BufMappingLock, the buffer header
> spinlock, and the buffer content lock. Second, instead of returning a
> pointer to the data in the page, we'll have to copy the data out of
> the buffer before releasing the pin.
The only way I can see this working is to optimise this in the
planner, so that when we have a nested loop within a loop, we avoid
having the row on the outer loop pinned while we perform the inner
loop.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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