From: | "Christopher Kings-Lynne" <chriskl(at)familyhealth(dot)com(dot)au> |
---|---|
To: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | "Hackers" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Solution to UPDATE...INSERT problem |
Date: | 2003-03-27 06:55:53 |
Message-ID: | 001901c2f42d$e8fd5f60$6500a8c0@fhp.internal |
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Lists: | pgsql-general pgsql-hackers |
> Uh, why exactly do you think this is race-free?
>
> It looks fancy, but AFAICS the SELECT will return info that is correct
> as of its starting timestamp; which is not enough to guarantee that the
> INSERT won't conflict with another transaction doing the same thing
> concurrently.
How about:
INSERT INTO table SELECT 1, 'foo' WHERE NOT EXISTS (SELECT TRUE FROM table
WHERE pkcol=1 FOR UPDATE);
It's a lot more straightforward and has a FOR UPDATE. Can this still cause
unique constraint failures?
Chris
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