Re: [HACKERS] MERGE SQL Statement for PG11

On 30 January 2018 at 16:27, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> As far as I am able to understand, the substantive issue here is what
> to do when we match an invisible tuple rather than a visible tuple.
> The patch currently throws a serialization error on the basis that you
> (Simon) thought that's what was previously agreed.

Correct. We discussed this and agreed point (3) below

> 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.

Acting in good faith, in respect of all of your wishes, I implemented
exactly that and not what I had personally argued in favour of.

> Peter is arguing
> that we don't normally issue a serialization error at READ COMMITTED
> (which I think is true) and proposed that we instead try to INSERT.

Which IMHO is case 4 since it would avoid a concurrent ERROR. This
meets exactly my original implementation goals as clearly stated on
this thread, so of course I agree with him and have already said I am
happy to change the code, though I am still wary of the dangers he
noted upthread.

If you now agree with doing that and are happy that there are no
dangers, then I'm happy we now have consensus again and we can
continue implementing MERGE for PG11.

This is a good outcome, thanks, our users will be happy.

--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services