Re: LWLOCK_STATS

On 07.01.2012 19:18, Tom Lane wrote:
> Heikki Linnakangas<heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
>> A couple of weeks ago I wrote a little patch that's similar to
>> LWLOCK_STATS, but it prints out % of wallclock time that is spent
>> acquiring, releasing, or waiting for a lock. I find that more useful
>> than the counters.
>
> I would think that the measurement overhead required to obtain two
> wall-clock values for every LWLock touch would be so high as to render
> any results from this quite suspect.

It's based on sampling. The timer calls a callback every X ms, which
checks if it's waiting for any lock at that moment, and bumps a counter
if so. In LWLockAcquire/Release you just set/reset a global status variable.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com