On August 18, 2016 7:44:50 AM PDT, Ants Aasma <ants.aasma@eesti.ee> wrote:
>On Tue, Aug 16, 2016 at 9:46 PM, Andres Freund <andres@anarazel.de>
>wrote:
>> On 2016-08-15 12:02:18 -0400, Robert Haas wrote:
>>> I am somewhat inclined to
>>> believe that we need to restructure the executor in a bigger way so
>>> that it passes around datums instead of tuples; I'm inclined to
>>> believe that the current tuple-centric model is probably not optimal
>>> even for the existing storage format.
>>
>> I actually prototyped that, and it's not an easy win so far. Column
>> extraction cost, even after significant optimization, is still often
>a
>> significant portion of the runtime. And e.g. projection only
>extracting
>> all columns, after evaluating a restrictive qual referring to an
>"early"
>> column, can be a significant win. We'd definitely have to give up on
>> extracting columns 0..n when accessing later columns... Hm.
>
>What about going even further than [1] in converting the executor to
>being opcode based and merging projection and qual evaluation to a
>single pass? Optimizer would then have some leeway about how to order
>column extraction and qual evaluation. Might even be worth it to
>special case some functions as separate opcodes (e.g. int4eq,
>timestamp_lt).
>
>Regards,
>Ants Aasma
>
>[1]
>https://www.postgresql.org/message-id/20160714011850.bd5zhu35szle3n3c@alap3.anarazel.de
Good question. I think I have a reasonable answer, but lets discuss that in the other thread.
Andres
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