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.
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