Re: profiling pgbench

On Wed, Nov 24, 2010 at 5:33 PM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
> On Wed, Nov 24, 2010 at 1:19 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>> On Wednesday 24 November 2010 22:14:04 Andres Freund wrote:
>>> On Wednesday 24 November 2010 21:24:43 Robert Haas wrote:
>>>
>>> Recarding LWLockAcquire costs:
>>> Yes, its pretty noticeable - on loads of different usages. On a bunch of
>>> production machines its the second (begind XLogInsert) on some the most
>>> expensive function. Most of the time
>
>> AllocSetAlloc is the third, battling with hash_search_with_hash value. To
>> complete that sentence...
>
> I've played a bit with hash_search_with_hash_value and found that most
> of the time is spent on shared hash tables, not private ones.  And the
> time attributed to it for the shared hash tables mostly seems to be
> due to the time it takes to fight cache lines away from other CPUs.  I
> suspect the same thing is true of LWLockAcquire.

How do you get stats on that?

How big is a typical cache line on modern CPUs?

--
Robert Haas
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