Re: Rename max_parallel_degree?
Josh Berkus <josh@agliodbs.com>
From: Josh berkus <josh@agliodbs.com>
To: Peter Geoghegan <pg@heroku.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>,
Noah Misch <noah@leadboat.com>, David Rowley <david.rowley@2ndquadrant.com>,
Amit Kapila <amit.kapila16@gmail.com>,
Alvaro Herrera <alvherre@2ndquadrant.com>,
Magnus Hagander <magnus@hagander.net>, Bruce Momjian <bruce@momjian.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2016-05-31T17:46:36Z
Lists: pgsql-hackers
On 05/31/2016 10:38 AM, Peter Geoghegan wrote: > On Tue, May 31, 2016 at 10:23 AM, Josh berkus <josh@agliodbs.com> wrote: >> It's still WAY simpler to understand "max_parallel is the number of >> parallel workers I requested". > > (Sorry Josh, somehow hit reply, not reply-all) > > Yes, it is. But as long as parallel workers are not really that > distinct to the leader-as-worker when executing a parallel query, then > you have another consideration. Which is that you need to care about > how many cores your query uses first and foremost, and not the number > of parallel workers used. I don't think that having only one worker > will cause too much confusion, because users will trust that we won't > allow something that simply makes no sense to happen. > > In my parallel create index patch, the leader participates as a worker > to scan and sort runs. It's identical to a worker, practically > speaking, at least until time comes to merge those runs. Similarly, > parallel aggregate does not really have much for the leader process to > do other than act as a worker. In parallel seq scan and join, do the "masters" behave as workers as well? -- -- Josh Berkus Red Hat OSAS (any opinions are my own)