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From: Thomas Kellerer <spam_eater@gmx.net>
To: pgsql-hackers@postgresql.org
Subject: Re: MERGE SQL Statement for PG11
Date: Fri, 3 Nov 2017 00:46:20 -0700 (MST)
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PMFJI

> We seem to have a few options for PG11
> 
> 1. Do nothing, we reject MERGE
> 
> 2. Implement MERGE for unique index situations only, attempting to
> avoid errors (Simon OP)
> 
> 3. Implement MERGE, but without attempting to avoid concurrent ERRORs
> (Peter)
> 
> 4. Implement MERGE, while attempting to avoid concurrent ERRORs in
> cases where that is possible.

From an end-users point of view I would prefer 3 (or 4 if that won't prevent
this from going into 11) 

INSERT ... ON CONFLICT is great, but there are situations where the
restrictions can get in the way and it would be nice to have an alternative
- albeit with some (documented) drawbacks. As far as I know Oracle also
doesn't guarantee that MERGE is safe for concurrent use - you can still wind
up with a unique key violation. 





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