Re: Performance issue with castings args of the function

[Андрей Хозов <avkhozov@xxxxxxxxx>]

Thanks all for explain!

On Mon, Jan 2, 2017 at 9:36 PM, Tom Lane <tgl@xxxxxxxxxxxxx> wrote:

=?UTF-8?B?0JDQvdC00YDQtdC5INCl0L7Qt9C+0LI=?= <avkhozov@xxxxxxxxx> writes:
> create table t1 (id serial, str char(32));

> create function f1(line text) returns void as $$
> begin
>   perform * from t1 where str = line;
> end;
> $$ language plpgsql;

This query is specifying a text comparison (text = text operator).
Since the table column isn't text, a char-to-text conversion must
happen at each line.

> create function f2(line char) returns void as $$
> begin
>   perform * from t1 where str = line;
> end;
> $$ language plpgsql;

This query is specifying a char(n) comparison (char = char operator).
No type conversion step needed, so it's faster.

                        regards, tom lane

--

​Andrey Khozov