Re: [HACKERS] MERGE SQL Statement for PG11

On 29 January 2018 at 16:50, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Bruce Momjian <bruce(at)momjian(dot)us> writes:
>> On Mon, Jan 29, 2018 at 04:34:48PM +0000, Simon Riggs wrote:
>>> ... If unfinished means it has caveats
>>> that is different to unfinished meaning crappy, risky, contentious
>>> etc..
>
>> I think the question is how does it handle cases it doesn't support?
>> Does it give wrong answers? Does it give a helpful error message? Can
>> you summarize that?
>
> What I was reacting to was the comments just upthread that it doesn't
> yet handle partitions or RLS. Those things don't seem optional to me.
> Maybe they're small additions, but if so why aren't they done already?

Phasing and risk.

Partitioning doesn't look too bad, so that looks comfortable for PG11,
assuming it doesn't hit some unhandled complexity.

Including RLS in the first commit/release turns this into a high risk
patch. Few people use it, but if they do, they don't want me putting a
hole in their battleship (literally) should we discover some weird
unhandled logic in a complex new command.

My recommendation would be to support that later for those that use
it. For those that don't, it doesn't matter so can also be done later.

> Also, as far as phased development goes: Simon's drawing analogies
> to things like parallel query, which we all understood had to be
> done over multiple dev cycles because they were too big to finish
> in one cycle. I don't think MERGE qualifies: there seems no good
> reason why it can't be done, full stop, in the first release where
> it appears.

That remains the plan, barring delays.

If you want to include RLS, then I would appreciate an early review.

--
Simon Riggs http://www.2ndQuadrant.com/
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