From: Andrew Dunstan <andrew@dunslane.net>
To: pgsql-perform <pgsql-performance@postgresql.org>
Subject: assignment vs SELECT INTO
Date: Mon, 03 Nov 2014 15:00:14 -0500
Message-ID: <5457DECE.3070302@dunslane.net> (raw)
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I found out today that direct assignment to a composite type is (at
least in my test) about 70% faster than setting it via SELECT INTO. That
seems like an enormous difference in speed, which I haven't really been
able to account for.
Test case:
andrew=# \d abc
Table "public.abc"
Column | Type | Modifiers
--------+---------+-----------
x | text |
y | text |
z | integer |
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?
cheers
andrew
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To: pgsql-performance@postgresql.org
Cc: andrew@dunslane.net
Subject: Re: assignment vs SELECT INTO
In-Reply-To: <5457DECE.3070302@dunslane.net>
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