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Re: [HACKERS] pow support for pgbench

Fabien COELHO <coelho@cri.ensmp.fr>

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From: Fabien COELHO <coelho@cri.ensmp.fr>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Raúl Marín Rodríguez <rmrodriguez@carto.com>, Tom Lane <tgl@sss.pgh.pa.us>, Michael Paquier <michael.paquier@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, PostgreSQL mailing lists <pgsql-hackers@postgresql.org>
Date: 2017-12-06T05:58:00Z
Lists: pgsql-hackers 
>> In both cases we'd return a double but we use the fast ipow if it's 
>> possible (which can be 20x faster), so at the cost of an extra cast if 
>> you need an int, we'd have a consistent API. Would this be acceptable?
>
> It seems OK to me.

Computing as an int, casting to double and back to int8 can generate a 
loss of precision. However for powers of 2 it works exactly, so eg 
computing a mask it would be ok.

This proposal does not exactly match SQL behavior, but I do not see this 
as a problem, which is why I was happy with the previous proposal.

-- 
Fabien.

Commits

  1. Add pow(), aka power(), function to pgbench.

  2. pgbench: Support double constants and functions.