Re: [PERFORM] Performance issue with castings args of the function

From: Tom Lane
Subject: Re: [PERFORM] Performance issue with castings args of the function
Date: ,
Msg-id: 18071.1483374980@sss.pgh.pa.us
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In response to: [PERFORM] Performance issue with castings args of the function  (Андрей Хозов)
Responses: Re: [PERFORM] Performance issue with castings args of the function  (Андрей Хозов)
List: pgsql-performance

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[PERFORM] Performance issue with castings args of the function  (Андрей Хозов, )
 Re: [PERFORM] Performance issue with castings args of the function  (Pavel Stehule, )
 Re: [PERFORM] Performance issue with castings args of the function  (Tom Lane, )
  Re: [PERFORM] Performance issue with castings args of the function  (Андрей Хозов, )

=?UTF-8?B?0JDQvdC00YDQtdC5INCl0L7Qt9C+0LI=?= <> 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



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