Message-ID: <5457E614.1030902@dunslane.net>
Date: Mon, 03 Nov 2014 15:31:16 -0500
From: Andrew Dunstan <andrew@dunslane.net>
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: pgsql-perform <pgsql-performance@postgresql.org>
Subject: Re: assignment vs SELECT INTO
References: <5457DECE.3070302@dunslane.net> <25915.1415046245@sss.pgh.pa.us>
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On 11/03/2014 03:24 PM, Tom Lane wrote:
> Andrew Dunstan <andrew@dunslane.net> writes:
>>      andrew=# do $x$ declare r abc; begin for i in 1 .. 10000000 loop
>>      select 'a','b',i into r.x,r.y,r.z; end loop; end; $x$;
>>      DO
>>      Time: 63731.434 ms
>>      andrew=# do $x$ declare r abc; begin for i in 1 .. 10000000 loop r
>>      := ('a','b',i); end loop; end; $x$;
>>      DO
>>      Time: 18744.151 ms
>> Is it simply because the SELECT is in effect three assignments, so it
>> takes nearly 3 times as long?
> I think it's more likely that the second example is treated as a "simple
> expression" so it has less overhead than a SELECT.
>
> 			


Well, I accidetally left out this case:

    andrew=# do $x$ declare r abc; begin for i in 1 .. 10000000 loop
    select row('a','b',i) into r; end loop; end; $x$;
    DO
    Time: 81919.721 ms


which is slower still.

cheers

andrew


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