Subject: Re: Additional LWLOCK_STATS statistics
To: Robert Haas <robertmhaas@gmail.com>
References: <55F82AE1.3010407@redhat.com>
 <CA+TgmoYvgL7rA6jBzn60FUeHhb5TH2xu2m9JKPiXFqbZ5Dyi7w@mail.gmail.com>
 <55F871BA.4060404@redhat.com>
 <CA+TgmoaXdUvA1P=-9PScZU5PMBEYeHw2XD4zF69=_LTU2zs+Wg@mail.gmail.com>
Cc: "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
From: Jesper Pedersen <jesper.pedersen@redhat.com>
Organization: JBoss, by Red Hat
Message-ID: <55F876CA.8020702@redhat.com>
Date: Tue, 15 Sep 2015 15:51:38 -0400
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101
 Thunderbird/38.1.0
MIME-Version: 1.0
In-Reply-To: 
 <CA+TgmoaXdUvA1P=-9PScZU5PMBEYeHw2XD4zF69=_LTU2zs+Wg@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org

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


-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers