On Wed, Oct 23, 2013 at 4:00 PM, Gavin Flower <gavinflo...@archidevsys.co.nz > wrote:
> On 24/10/13 11:26, Peter Geoghegan wrote: > >> On Wed, Oct 23, 2013 at 2:57 PM, Gavin Flower >> <gavinflo...@archidevsys.co.nz**> wrote: >> >>> Looks definitely bimodal in the log version, very clear! >>> >>> Yes, I feel that having a 32 log binary binned histogram (as Alvaro >>> Herrera >>> suggested) would be very useful. >>> >> I'm having a hard time imagining how you'd actually implement that. >> For example, this: >> >> https://wiki.postgresql.org/**wiki/Aggregate_Histogram<https://wiki.postgresql.org/wiki/Aggregate_Histogram> >> >> requires that a "limit" be specified ahead of time. Is there a >> principled way to increase or decrease this kind of limit over time, >> and have the new buckets contents "spill into each other"? >> >> To smplify things, I'm using 5 buckets, but 32 would be better. > Assume first bucket width is 1ms. > > bucket range > 0 x =< 1ms > 1 1ms < x =< 2ms > 2 2ms < x =< 4ms > 3 4ms < x =< 8ms > 5 8ms < x > The last bucket would be limited to 8ms < x <= 16 ms. If you find something > 16ms, then you have to rescale *before* you increment any of the buckets. Once you do, there is now room to hold it. bucket range 0 x =< 2ms (sum of previous bucket 0 and previous bucket 1) 1 2ms < x =< 4ms 2 4ms < x =< 8ms 3 8ms < x =< 16ms 4 16ms < x =< 32ms (starts empty) Cheers, Jeff
