Re: That EXPLAIN ANALYZE patch still needs work

It would be nice to keep the gettimeofday()s wherever they are most useful
on hardware/software where they are cheap. Perhaps a compile-time option?

On Fri, June 9, 2006 11:18 am, Martijn van Oosterhout wrote:
> On Fri, Jun 09, 2006 at 10:00:20AM -0400, Tom Lane wrote:
>
>> To tell you the truth, this information makes me even less pleased with
>>  the sampling-gettimeofday patch than I was before.  If gettimeofday()
>> in itself increases the runtime of a node by a factor of 10, then just
>> trying to subtract off that time is no solution.  There's too much
>> impact on surrounding nodes, and too much roundoff error anyhow. I had
>> thought we were applying an order-of-ten-percent correction by
>> subtracting SampleOverhead, not an order-of-10x correction :-(
>
> Eh? The whole point is to call gettimeofday() much less often. If you
> call it 1000th as often, then the correction is only on the order of one
> hundredth of the normal query time...
>
> Subtracting SampleOverhead is only a correction on the order of a few
> percent, it's the reduced calling of gettimeofday() that provides the
> benefit.
>
> Have a nice day,
> --
> Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
>
>> From each according to his ability. To each according to his ability to
>> litigate.
>