| From: | Noah Misch <noah(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: sinval synchronization considered harmful |
| Date: | 2011-07-21 22:43:29 |
| Message-ID: | 20110721224326.GA27478@tornado.leadboat.com |
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| Lists: | pgsql-hackers |
On Wed, Jul 20, 2011 at 09:46:33PM -0400, Robert Haas wrote:
> Profiling this combination of patches reveals that there is still some
> pretty ugly spinlock contention on sinval's msgNumLock. And it occurs
> to me that on x86, we really don't need this lock ... or
> SInvalReadLock ... or a per-backend mutex. The whole of
> SIGetDataEntries() can pretty easily be made lock-free. The only real
> changes that seem to be are needed are (1) to use a 64-bit counter, so
> you never need to decrement
On second thought, won't this be inadequate on 32-bit systems, where updating
the 64-bit counter produces two stores? You must avoid reading it between those
stores.
--
Noah Misch http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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