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Re: gSoC add MERGE command new patch -- merge_v104

Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>

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From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
To: Andres Freund <andres@anarazel.de>
Cc: Boxuan Zhai <bxzhai2010@gmail.com>, pgsql-hackers@postgresql.org
Date: 2010-08-25T06:26:51Z
Lists: pgsql-hackers 
On 24/08/10 23:56, Andres Freund wrote:
> I have to ask one question: On a short review of the discussion and
> the patch I didn't find anything about the concurrency issues
> involved (at least nodeModifyTable.c didnt show any).

The SQL spec doesn't require MERGE to be an atomic "upsert" operation.

> Whats the plan to go forward at that subject? I think the patch needs
> to lock tables exclusively (the pg level, not access exclusive) as
> long as there is no additional handling...

Well, you can always do LOCK TABLE before calling MERGE if that's what 
you want, but I don't think doing that automatically would make people 
happy.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com