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  1. Add a planner support function for numeric generate_series().

  1. Added prosupport function for estimating numeric generate_series rows

    songjinzhou <tsinghualucky912@foxmail.com> — 2024-11-28T07:46:47Z

    Hello hackers, I saw a recent submission: Teach planner how to estimate rows for timestamp generate_series. I provide a patch for the numeric type here, and a simple test is as follows:


postgres=# explain SELECT * FROM generate_series(-25.0, -1.0, 2.0);
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; QUERY PLAN &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
----------------------------------------------------------------------
&nbsp;Function Scan on generate_series &nbsp;(cost=0.00..0.13 rows=13 width=32)
(1 row)


postgres=# explain SELECT * FROM generate_series(-25.0, -1.0); &nbsp; &nbsp;
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; QUERY PLAN &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
----------------------------------------------------------------------
&nbsp;Function Scan on generate_series &nbsp;(cost=0.00..0.25 rows=25 width=32)
(1 row)


postgres=#


I really want to know your thoughts, please give me feedback. Thank you.

  2. Re: Added prosupport function for estimating numeric generate_series rows

    Dean Rasheed <dean.a.rasheed@gmail.com> — 2024-11-28T13:56:10Z

    On Thu, 28 Nov 2024 at 07:47, 孤傲小二~阿沐 <tsinghualucky912@foxmail.com> wrote:
>
> Hello hackers, I saw a recent submission: Teach planner how to estimate rows for timestamp generate_series. I provide a patch for the numeric type here, and a simple test is as follows:
>
> I really want to know your thoughts, please give me feedback. Thank you.
>

Good idea.

Some random review comments:

This should test for special inputs, NaN and infinity (it doesn't make
sense to convert those to NumericVars). generate_series() produces an
error for all such inputs, so the support function can just not
produce an estimate for these cases (the same as when the step size is
zero).

NumericVars initialised using init_var() should be freed using
free_var(). That can be avoided for the 3 inputs, by using
init_var_from_num(), rather than set_var_from_num(), which saves
copying digit arrays. It should then be possible to write this using a
single additional allocated NumericVar and one init_var()/free_var()
pair.

There's no need to use floor(), since the div_var() call already
produces a floored integer result.

It could use some regression test cases.

Regards,
Dean