Re: [HACKERS] pow support for pgbench

From: Raúl Marín Rodríguez <rmrodriguez(at)carto(dot)com>
To: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, PostgreSQL mailing lists <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] pow support for pgbench
Date: 2017-12-22 08:46:31
Message-ID: CAM6_UM7J4Jo+6OFdQg4KOCzHa8+DP3r-PAajkY-UX4zehsr+Dw@mail.gmail.com
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Hi Fabien,

Thanks for the review.

If a double is always returned, I'm wondering whether keeping the ipow
> version makes much sense: In case of double loss of precision, the
> precision is lost, too bad, and casting back to int won't bring it back.

I've kept it because knowing that both are ints enables not making a lot of
checks (done in math.h pow) so it's way faster. In my system it's 2-3ns vs
~40ns. I'm willing to settle for using just pow() if that makes it clearer.

In the doc, I'm not sure that "Numeric" brings anything. "Exponentiation"
> would be enough.

Done.

Also, in pg I just noticed that POW is a shorthand for POWER. Maybe both
> should be supported? Or not.

I've never used power instead of pow, but I've added for compatibility
shake.

Attached the updated patch.

On Thu, Dec 21, 2017 at 10:48 PM, Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> wrote:

>
> Hello Raúl,
>
> v7 needs a rebase.
>>>
>>> Also, you might try to produce a version which is compatible with
>>> Robert's
>>> constraints.
>>>
>>
> My 0.02€ on this new version: Applies cleanly, compiles and works.
>
> I cannot say that I like it more than the previous version.
>
> If a double is always returned, I'm wondering whether keeping the ipow
> version makes much sense: In case of double loss of precision, the
> precision is lost, too bad, and casting back to int won't bring it back.
>
> In the doc, I'm not sure that "Numeric" brings anything. "Exponentiation"
> would be enough.
>
> Also, in pg I just noticed that POW is a shorthand for POWER. Maybe both
> should be supported? Or not.
>
> --
> Fabien.

--

*Raúl Marín Rodríguez *carto.com

Attachment Content-Type Size
pgbench_pow_v9.patch text/x-patch 5.1 KB

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