Re: Parallel Index Scans

On Tue, Jan 31, 2017 at 5:53 PM, Rahila Syed <rahilasyed90@gmail.com> wrote:
> Hello,
>
>>Agreed, that it makes sense to consider only the number of pages to
>>scan for computation of parallel workers.  I think for index scan we
>>should consider both index and heap pages that need to be scanned
>>(costing of index scan consider both index and heap pages).   I thin
>>where considering heap pages matter more is when the finally selected
>>rows are scattered across heap pages or we need to apply a filter on
>>rows after fetching from the heap.  OTOH, we can consider just pages
>>in the index as that is where mainly the parallelism works
> IMO, considering just index pages will give a better estimate of work to be
> done
> in parallel. As the amount of work/number of pages divided amongst workers
> is irrespective of
> the number of heap pages scanned.
>

Yeah, I understand that point and I can see there is strong argument
to do that way, but let's wait and see what others including Robert
have to say about this point.


-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com