Bruce Momjian wrote:

Btw., I was wondering, are we kidding ourselves when we display
microsecond precision to the user? What accuracy do these measurements
have in respect to what they are actually supposed to measure?

Not sure. I think the microsecond stuff is accurate to some degree, but not sure how much. I think the tick is 10ms, but I thought the timing was much more accurate than that.

On my (slow) linux box the apparent time delay between 2 immediately successive calls to gettimeofday() is 3 or 4 microsecs.

Presumably the clock tick is something much larger than that - I forget where to look to find that out.

I think the real question is what granularity of reporting will be most useful. For the session duration patch I restricted it to 1/100th of a second, and didn't bother rounding the last place there because it wasn't worth it (I thought). For query duration presumably something smaller seems appropriate, but I'm not sure how small. I suspect anything much below a millisec (or at most 100 microsecs) is of comparatively little value. OTOH truncating it is also probably of little value - if you can read 3 or 4 decimal places you can read 6 just as easily - just be aware that the low values have little information value.



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