From: Jesper Pedersen <jesper.pedersen@redhat.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: pgsql-hackers@postgresql.org <pgsql-hackers@postgresql.org>
Subject: Re: Additional LWLOCK_STATS statistics
Date: Tue, 15 Sep 2015 15:51:38 -0400
Message-ID: <55F876CA.8020702@redhat.com> (raw)
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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
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To: pgsql-hackers@postgresql.org
Cc: jesper.pedersen@redhat.com, robertmhaas@gmail.com
Subject: Re: Additional LWLOCK_STATS statistics
In-Reply-To: <55F876CA.8020702@redhat.com>
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