To: pgsql-performance@postgresql.org
From: Anton Bogdanovitch <poison.box@gmail.com>
Subject: perform 1 check vs exception when unique_violation
Date: Tue, 30 Dec 2008 13:41:42 +0300
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I have to insert rows to table with 95% primary key unique_violation.

I've tested 2 examples below:

1)
BEGIN
    INSERT INTO main (name, created) VALUES (i_name, CURRENT_TIMESTAMP
AT TIME ZONE 'GMT');
    EXCEPTION WHEN UNIQUE_VIOLATION THEN
       RETURN 'error: already exists';
END;
RETURN 'ok: store';

2)
PERFORM 1 FROM main WHERE name = i_name;
IF NOT FOUND THEN
    INSERT INTO main (name, created) VALUES (i_name, CURRENT_TIMESTAMP
AT TIME ZONE 'GMT');
    RETURN 'ok: stored';
ELSE
    RETURN 'error: already exists';
END IF;

The first one performs about 20% slower, have 5 times more disk i/o
write operations.
The second one uses 20% more cpu.
Is it because of raid1 and slow writes?
What is the better solution to fit best performance?
Pg version 8.3, table size will probably grow to 100M rows