Re: sinval synchronization considered harmful

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/
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