From: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com> |
---|---|
To: | Peter Geoghegan <pg(at)heroku(dot)com> |
Cc: | Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz>, 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 23:06:35 |
Message-ID: | CAMkU=1wgbyA9AT9TUBmOM29C4nwGnaBm9T6pu_cAkdP05N358A@mail.gmail.com |
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Lists: | pgsql-hackers |
On Wed, Oct 23, 2013 at 3:26 PM, Peter Geoghegan <pg(at)heroku(dot)com> 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"?
>
If you are doing a log scale in the bucket widths, 32 buckets covers a huge
range, so I think you could get away without having the ability to rescale
at all. For example just have the bottom bucket mean <=1ms, and the top
bucket mean > 12.42 days (rather than between 12.42 and 24.85 days). But
it should be possible to rescale if you really want to. If a bucket >32 is
needed, just add bucket[2] into bucket[1], slide buckets 3..32 down one
each, and initialize a new bucket 32, and bump the factor that says how
many times this shift has been done before.
Cheers,
Jeff
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