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
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
If the size of the first bucket changed, then implicitly the histogram
would be restarted. As there is no meaningful way of using any data
from the existing histogram - even if the size of the first bucket was a
power of 2 greater than the old one (here things are fine, until you try
and apportion the data in the last bucket!).
Cheers,
Gavin
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