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

On Sun, Feb 5, 2017 at 9:19 PM, Kouhei Kaigai <kaigai@ak.jp.nec.com> wrote:
>> If the use case for this is to gather instrumentation, I'd suggest calling
>> the hook in RetrieveInstrumentation, and calling it appropriately. It would
>> make the intended use far clearer than it is now.
>>
>> And if it saves some work, all the better.
>>
>> Until there's a use case for a non-instrumentation hook in that place, I
>> wouldn't add it. This level of generality sounds like a solution waiting
>> for a problem to solve.
>>
> The use cases I'd like to add are extension specific but significant for
> performance analytics. These statistics are not included in Instrumentation.
> For example, my problems are GPU execution time, data transfer ratio over
> DMA, synchronization time for GPU task completion, and so on.
> Only extension can know which attributes are collected during the execution,
> and its data format. I don't think Instrumentation fits these requirements.
> This is a problem I faced on the v9.6 based interface design, so I could
> notice it.


What RetrieveInstrumentation currently does may not cover the
extension's specific instrumentation, but what I'm suggesting is
adding a hook, like the one you're proposing for ParallelFinish, that
would collect extension-specific instrumentation. Couple that with
extension-specific explain output and you'll get your use cases
covered, I think.