Re: pg_stat_lwlocks view - lwlocks statistics, round 2

Satoshi Nagayasu <snaga(at)uptime(dot)jp> writes:
> (2012/10/14 13:26), Fujii Masao wrote:
>> The tracing lwlock usage seems to still cause a small performance
>> overhead even if reporting is disabled. I believe some users would
>> prefer to avoid such overhead even if pg_stat_lwlocks is not available.
>> It should be up to a user to decide whether to trace lwlock usage, e.g.,
>> by using trace_lwlock parameter, I think.

> Frankly speaking, I do not agree with disabling performance
> instrument to improve performance. DBA must *always* monitor
> the performance metrix when having such heavy workload.

This brings up a question that I don't think has been honestly
considered, which is exactly whom a feature like this is targeted at.
TBH I think it's of about zero use to DBAs (making the above argument
bogus). It is potentially of use to developers, but a DBA is unlikely
to be able to do anything about lwlock-level contention even if he has
the knowledge to interpret the data.

So I feel it isn't something that should be turned on in production
builds. I'd vote for enabling it by a non-default configure option,
and making sure that it doesn't introduce any overhead when the option
is off.

regards, tom lane