Re: Additional LWLOCK_STATS statistics

On Wed, Sep 16, 2015 at 1:21 AM, Jesper Pedersen <jesper(dot)pedersen(at)redhat(dot)com>
wrote:
>
> On 09/15/2015 03:42 PM, Robert Haas wrote:
>>
>> I haven't really, just the email. But it seems like a neat concept.
>> So if I understand this correctly:
>>
>> 74.05% of spin delays are attributable to CLogControLock, 20.01% to
>> ProcArrayLock, and 3.39% to XidGenLock. Incredibly, the queue length
>> reaches the number of backends (80) for both CLogControlLock and
>> XidGenLock, but for ProcArrayLock it "only" reaches a length of 75.
>>
>
> 74, as the "real" information is above the "call stack". The spin delay
report is filtered on > 0 - so only LWLock's that has any spin delay are
included.
>
> Only the weight report shows all locks.
>
>> This seems to suggest that relieving pressure on CLogControlLock would
>> be very beneficial, but I'm not sure what else to make of it.
>
>
> I have done some runs with Amit's CLogControlLock patch, but currently it
doesn't show any improvements. I'm trying to figure out why.
>

Thanks for testing the patch. I think even if you are not getting
improvement, feel free to report about it with details. I can also
look into it that why it is not showing improvement.

Two important points to care about while testing that patch are that
data should fit in shared_buffers and synchronous_commit should be
on, for other kind of workloads it might or might not give much benefit.

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com