Josh berkus <josh@agliodbs.com> writes:
> On 05/31/2016 11:10 AM, Tom Lane wrote:
>> The 9.6 open-items list cites
>> https://www.postgresql.org/message-id/flat/20160420174631.3qjjhpwsvvx5bau5@alap3.anarazel.de
> Looks like we didn't decide for the release, just the beta.
Indeed. I think it's premature to have this discussion. The plan
was to evaluate near the end of beta, when we (hopefully) have a
better feeling for how buggy parallel query is likely to be.
> Also, defaulting to off lets users make more use of the parallel_degree
> table attribute to just enable parallelism on select tables.
Well, that's an interesting point. The current coding is that
parallel_degree is an upper limit on per-table workers, and
max_parallel_degree also limits it. So if you want parallel scans only on
a small set of tables, parallel_degree is not an especially convenient way
to get to that. Whether we measure it in workers or cores doesn't change
this conclusion.
It might be worth reconsidering what per-table knobs we should provide
exactly, but that's orthogonal to the main point under discussion.
regards, tom lane