From: | Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz> |
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To: | Peter Geoghegan <pg(at)heroku(dot)com> |
Cc: | Marc Mamin <M(dot)Mamin(at)intershop(dot)de>, KONDO Mitsumasa <kondo(dot)mitsumasa(at)lab(dot)ntt(dot)co(dot)jp>, Stephen Frost <sfrost(at)snowman(dot)net>, Dimitri Fontaine <dimitri(at)2ndquadrant(dot)fr>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Add min and max execute statement time in pg_stat_statement |
Date: | 2013-10-23 23:07:09 |
Message-ID: | 5268569D.6000404@archidevsys.co.nz |
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Lists: | pgsql-hackers |
On 24/10/13 12:00, Gavin Flower wrote:
> On 24/10/13 11:26, Peter Geoghegan wrote:
>> On Wed, Oct 23, 2013 at 2:57 PM, Gavin Flower
>> <GavinFlower(at)archidevsys(dot)co(dot)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
>
>
Arghhhhh!
Just realized, that even if the size of the first bucket was a power of
2 greater than the old one, then you can't meaningfully use any of the
old data in any of the old buckets (this is 'obvious; but somewhat messy
to explain!)
Cheers,
Gavin
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