Re: heap vacuum & cleanup locks

On Tue, Jun 7, 2011 at 8:24 PM, Greg Stark <gsstark(at)mit(dot)edu> wrote:
> On Mon, Jun 6, 2011 at 11:30 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> But I think you've hit the important point here. The problem is not
>> whether VACUUM waits for the pin, its that the pins can be held for
>> extended periods.
>
> Yes
>
>> It makes more sense to try to limit pin hold times than it does to
>> come up with pin avoidance techniques.
>
> Well it's super-exclusive-vacuum-lock avoidance techniques. Why
> shouldn't it make more sense to try to reduce the frequency and impact
> of the single-purpose outlier in a non-critical-path instead of
> burdening every other data reader with extra overhead?
>
> I think Robert's plan is exactly right though I would phrase it
> differently. We should get the exclusive lock, freeze/kill any xids
> and line pointers, then if the pin-count is 1 do the compaction.

Would that also be possible during recovery?

A similar problem exists with Hot Standby, so I'm worried fixing just
VACUUMs would be a kluge.

--
 Simon Riggs                   http://www.2ndQuadrant.com/
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