Re: [HACKERS] pg_stat_activity.waiting_start

On 12/28/16 7:10 AM, Amit Kapila wrote:
> Can we think of introducing new guc trace_system_waits or something
> like that which will indicate that the sessions will report the value
> of wait_start in pg_stat_activity?  The default value of such a
> parameter can be false which means wait_start will be shown as NULL in
> pg_stat_activity and when it is enabled the wait_start can show the
> time as proposed in this thread.

In my experience the problem with those kind of settings is that they're 
never enabled when you actually need them. I think it'd be much better 
to find a way to always capture wait_starts that are over some minimum 
duration, where collection overhead won't matter but you still have some 
good info about what's going on. For pg_stat_activity I'd think that 
threshold would be on the order of 50-100ms, though maybe there's other 
places where a tighter tolerance would help.
-- 
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
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