Re: Additional LWLOCK_STATS statistics

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.

> It
> would be nice to get a better sense of how *long* we block on various
> locks. It's hard to tell whether some other lock might be have fewer
> blocking events but for a much longer average duration.
>

Yes, that would be interesting.

Best regards,
Jesper