Re: Add min and max execute statement time in pg_stat_statement

On 24/10/13 11:26, Peter Geoghegan wrote:
> On Wed, Oct 23, 2013 at 2:57 PM, Gavin Flower
> <GavinFlower@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