Re: [HACKERS] why not parallel seq scan for slow functions

On Thu, Aug 17, 2017 at 2:45 PM, Dilip Kumar <dilipbalaut@gmail.com> wrote:
> On Thu, Aug 17, 2017 at 2:09 PM, Dilip Kumar <dilipbalaut@gmail.com> wrote:
>>
>> Either we can pass "num_gene" to merge_clump or we can store num_gene
>> in the root. And inside merge_clump we can check. Do you see some more
>> complexity?
>>

I think something like that should work.

> After putting some more thought I see one more problem but not sure
> whether we can solve it easily. Now, if we skip generating the gather
> path at top level node then our cost comparison while adding the
> element to pool will not be correct as we are skipping some of the
> paths (gather path).  And, it's very much possible that the path1 is
> cheaper than path2 without adding gather on top of it but with gather,
> path2 can be cheaper.
>

I think that should not matter because the costing of gather is mainly
based on a number of rows and that should be same for both path1 and
path2 in this case.

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