Re: Parallel Seq Scan

On Tue, Apr 21, 2015 at 9:38 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> On Mon, Apr 20, 2015 at 10:08 PM, Robert Haas <robertmhaas@gmail.com> wrote:
>>
>> On Tue, Apr 7, 2015 at 11:58 PM, Amit Kapila <amit.kapila16@gmail.com>
>> wrote:
>> > One disadvantage of retaining parallel-paths could be that it can
>> > increase the number of combinations planner might need to evaluate
>> > during planning (in particular during join path evaluation) unless we
>> > do some special handling to avoid evaluation of such combinations.
>>
>> Yes, that's true.  But the overhead might not be very much.  In the
>> common case, many baserels and joinrels will have no parallel paths
>> because the non-parallel paths is known to be better anyway.  Also, if
>> parallelism does seem to be winning, we're probably planning a query
>> that involves accessing a fair amount of data,
>
> Am I understanding right that by above you mean to say that retain the
> parallel and non-parallel path only if parallel-path wins over non-parallel
> path?

Yes.

-- 
Robert Haas
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