On Sat, Mar 25, 2006 at 04:24:05PM +0100, Martijn van Oosterhout wrote: > I agree. However, if it's the overhead of calling gettimeofday() that > slows everything down, perhaps we should tackle that end. For example, > have a sampling mode that only times say 5% of the executed nodes. > > EXPLAIN ANALYZE SAMPLE blah;
<snip>
> You could do a non-random sampling fairly easily:
Actually, I thought of a better way to control the sampling that's
probably better than the crude if-then-else structure I gave which also
takes advantage of the fact that the numbers are floating point:
InstrInit:
next_sample = 0;
InstrStart:
if( ntuples < 16 )
dosample = yes;
else if( ntuples > next_sample )
{
dosample = yes;
next_sample += log2(ntuples);
}
else
dosample = no;
This will sample approxiamtly log2 of the actual executions. You could
use log10(), sqrt() or any other function you find reflects the sample
you want.
Have a nice day,
--
Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.
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