MERGE just landed for #postgresql 15.
I had this on my list of "I really hope it makes it, but it's a tough one" list from my talk at
I am very glad it made it! Thanks for keeping up to the finish line, and team!
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So what does MERGE do that you couldn’t do with INSERT … ON CONFLICT UPDATE?
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Right, but the downside is that MERGE's MVCC snapshot might not be able to see a concurrently inserted tuple, go on to insert (instead of say updating the other session's row), then get a unique violation. AFAICT you can't have generality of MERGE without accepting that downside.
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That seems right to me, but I'd expect high level application requirements to drive the choice to use one over the other