Re: [PATCH] Negative Transition Aggregate Functions (WIP)

From: David Rowley <dgrowleyml(at)gmail(dot)com>
To: Florian Pflug <fgp(at)phlo(dot)org>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Kevin Grittner <kgrittn(at)ymail(dot)com>, Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Greg Stark <stark(at)mit(dot)edu>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [PATCH] Negative Transition Aggregate Functions (WIP)
Date: 2014-01-23 00:07:29
Message-ID: CAApHDvrNnQY5J8tJZ249KNaJHZbC=ptBc+O-3T2OkVL6oH5Szw@mail.gmail.com
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On Tue, Jan 21, 2014 at 3:20 AM, Florian Pflug <fgp(at)phlo(dot)org> wrote:

> On Jan20, 2014, at 08:42 , David Rowley <dgrowleyml(at)gmail(dot)com> wrote:
> >> On Mon, Jan 20, 2014 at 2:45 PM, Florian Pflug <fgp(at)phlo(dot)org> wrote:
> >> * I've also renamed INVFUNC to INVSFUNC. That's a pretty invasive
> change, and
> >> it's the last commit, so if you object to that, then you can merge up
> to
> >> eafa72330f23f7c970019156fcc26b18dd55be27 instead of
> >> de3d9148be9732c4870b76af96c309eaf1d613d7.
> >
> >
> > Seems like sfunc really should be tfunc then we could have invtfunc. I'd
> probably
> > understand this better if I knew what the 's' was for in sfunc. I've not
> applied
> > this just yet. Do you have a reason why you think it's better?
>
> My issue with just "invfunc" is mainly that it's too generic - it doesn't
> tell
> you what it's supposed to be the inverse of.
>
> I've always assumed that 's' in 'sfunc' and 'stype' stands for 'state',
> and that
> the naming is inspired by control theory, where the function which acts on
> the
> state space is often called S.
>
>
Ok, that makes more sense now and it seems like a reasonable idea. I'm not
not quite sure yet as when someone said upthread that these "negative
transition functions" as I was calling them at the time should really be
called "inverse transition functions", I then posted that I was going to
call the create aggregate option "invfunc" which nobody seemed to object
to. I just don't want to go and change that now. It is very possible this
will come up again when the committer is looking at the patch. It would be
a waste if it ended up back at invfunc after we changed it to invsfunc.

Regards

David Rowley

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