Re: ParallelFinish-hook of FDW/CSP (Re: [HACKERS] Steps inside ExecEndGather)

On Mon, Feb 6, 2017 at 1:42 AM, Kouhei Kaigai <kaigai@ak.jp.nec.com> wrote:
> I also had thought an idea to have extra space to Instrumentation structure,
> however, it needs to make Instrumentation flexible-length structure according
> to the custom format by CSP/FDW. Likely, it is not a good design.
> As long as extension can retrieve its custom statistics on DSM area required
> by ExecParallelEstimate(), I have no preference on the hook location.

That's what I had in mind: the hook happens there, but the extension
retrieves the information from some extension-specific DSM area, just
as it would on the ParallelFinish hook.

> One thing we may pay attention is, some extension (not mine) may want to
> collect worker's statistics regardless of Instrumentation (in other words,
> even if plan is not under EXPLAIN ANALYZE).
> It is the reason why I didn't put a hook under the ExecParallelRetrieveInstrumentation().

I don't think you should worry about that as long as it's a hypothetical case.

If/when some extension actually needs to do that, the design can be
discussed with a real use case at hand, and not a hypothetical one.