Re: SSI atomic commit

On Tue, Jul 5, 2011 at 2:35 PM, Kevin Grittner
<Kevin.Grittner@wicourts.gov> wrote:
>> It'd be better to push some functionality into the procarray code.
>
> That's easily done if we don't mind taking out a ProcArrayLock
> during completion of a transaction which has no XID, if only long
> enough to increment a uint64 in shared memory, and then stash the
> value -- somewhere -- so that SSI code can find and use it.

That sure sounds scary from a scalability perspective.  If we can
piggyback on an existing ProcArrayLock acquisition, fine, but
additional ProcArrayLock acquisitions when SSI isn't even being used
sound like a real bad idea to me.  I doubt you'll notice much of a
performance regression in the current code, but if/when we fix the
lock manager bottlenecks that my fastlock and lazy vxid lock patches
are intended to correct, then I suspect it's going to matter quite a
bit.

-- 
Robert Haas
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