Re: Additional LWLOCK_STATS statistics - Mailing list pgsql-hackers

From Amit Kapila
Subject Re: Additional LWLOCK_STATS statistics
Date
Msg-id CAA4eK1LsLvC7c2M2nKokYLT+m7sM5UhLAGS1KeHFQ3pbK5A_JA@mail.gmail.com
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In response to Re: Additional LWLOCK_STATS statistics  (Jesper Pedersen <jesper.pedersen@redhat.com>)
List pgsql-hackers
On Wed, Sep 16, 2015 at 1:21 AM, Jesper Pedersen <jesper.pedersen@redhat.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

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