| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Jim Nasby <jim(at)nasby(dot)net>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Daniel Farina <daniel(at)heroku(dot)com>, Merlin Moncure <mmoncure(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Removing freelist (was Re: Should I implement DROP INDEX CONCURRENTLY?) |
| Date: | 2012-01-23 16:01:52 |
| Message-ID: | 205.1327334512@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Mon, Jan 23, 2012 at 12:12 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> The expensive part of what
>>> we do while holding BufFreelistLock is, I think, iterating through
>>> buffers taking and releasing a spinlock on each one (!).
>> Yeah ... spinlocks that, by definition, will be uncontested.
> What makes you think that they are uncontested?
Ah, never mind. I was thinking that we'd only be touching buffers that
were *on* the freelist, but of course this is incorrect. The real
problem there is that BufFreelistLock is also used to protect the
clock sweep pointer. I think basically we gotta find a way to allow
multiple backends to run clock sweeps concurrently. Or else fix
things so that the freelist never (well, hardly ever) runs dry.
regards, tom lane
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