On Tue, Jul 26, 2011 at 7:24 PM, Alvaro Herrera
<alvherre@commandprompt.com> wrote:
> Excerpts from Simon Riggs's message of mar jul 26 14:11:19 -0400 2011:
>
>> Let me ask a few questions to stimulate a different solution
>>
>> * Can we do this using an active technique (e.g. signals) rather than
>> a passive one (reading a counter?)
>
> Signals are already in use for special cases (queue is full), and I
> think going through the kernel to achieve much more will lower
> performance significantly.
If there are no invalidations, there would be no signals. How would
zero signals decrease performance?
>> * Can we partition the sinval lock, so we have multiple copies? That
>> increases the task for those who trigger an invalidation, but will
>> relieve the pressure for most readers.
>
> Not sure there's a way to meaningfully partition the queue. In any
> case, I think the problem being dealt with here is how to update the
> read heads of the queue, not its contents.
I agree there's no meaningful way to partition the queue, but we can
store the information in more than one place to reduce the contention
of people requesting it.
Both those ideas are still on the table.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services