Re: [HACKERS] Cost model for parallel CREATE INDEX

On Sat, Mar 4, 2017 at 2:01 PM, Peter Geoghegan <pg@bowt.ie> wrote:
> On Sat, Mar 4, 2017 at 12:23 AM, Robert Haas <robertmhaas@gmail.com> wrote:
>>> I guess that the workMem scaling threshold thing could be
>>> min_parallel_index_scan_size, rather than min_parallel_relation_size
>>> (which we now call min_parallel_table_scan_size)?
>>
>> No, it should be based on min_parallel_table_scan_size, because that
>> is the size of the parallel heap scan that will be done as input to
>> the sort.
>
> I'm talking about the extra thing we do to prevent parallelism from
> being used when per-worker workMem is excessively low. That has much
> more to do with projected index size than current heap size.

Oh.  But then I don't see why you need min_parallel_anything.  That's
just based on an estimate of the amount of data per worker vs.
maintenance_work_mem, isn't it?

-- 
Robert Haas
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