|From:||Jeff Davis <pgsql(at)j-davis(dot)com>|
|To:||Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>|
|Cc:||Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org|
|Subject:||Re: Removing PD_ALL_VISIBLE|
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On Mon, 2013-01-21 at 12:00 +0200, Heikki Linnakangas wrote:
> On 21.01.2013 11:10, Jeff Davis wrote:
> > That confuses me. The testing was to show it didn't hurt other workloads
> > (like scans or inserts/updates/deletes); so the best possible result is
> > that they don't show signs either way.
> I went back to look at the initial test results that demonstrated that
> keeping the pin on the VM buffer mitigated the overhead of pinning the
> vm page. The obvious next question is, what is the impact when that's
> inefficient, ie. when you update pages across different 512 MB sections,
> so that the vm pin has to be dropped and reacquired repeatedly.
> I tried to construct a worst case scenario for that:
I confirmed this result in a single connection (no concurrency). I used
a shared_buffers of 2GB so that the whole table would fit.
Also, I fixed a bug that I noticed along the way, which was an
uninitialized variable. New version attached.
FWIW, I'm considering this patch to be rejected; I just didn't want to
leave a patch with a bug in it.
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