Re: Rename max_parallel_degree?
Robert Haas <robertmhaas@gmail.com>
From: Robert Haas <robertmhaas@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Julien Rouhaud <julien.rouhaud@dalibo.com>,
Josh Berkus <josh@agliodbs.com>, "David G. Johnston" <david.g.johnston@gmail.com>,
Amit Kapila <amit.kapila16@gmail.com>, Peter Geoghegan <pg@heroku.com>, Noah Misch <noah@leadboat.com>, David Rowley <david.rowley@2ndquadrant.com>,
Alvaro Herrera <alvherre@2ndquadrant.com>, Magnus Hagander <magnus@hagander.net>, Bruce Momjian <bruce@momjian.us>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2016-06-14T17:07:25Z
Lists: pgsql-hackers
On Tue, Jun 14, 2016 at 12:16 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote: > Robert Haas <robertmhaas@gmail.com> writes: >> Of course, it would be nice if we could make these counters 64-bit >> integers, but we can't, because we don't rely on 64-bit reads and >> writes to be atomic on all platforms. So instead they'll have to be >> uint32. That means they could wrap (if you really work at it) but >> subtraction will still return the right answer, so it's OK. > > OK ... > >> If we >> want to allow the number of parallel workers started to be available >> for statistical purposes, we can keep to uint32 values for that >> (parallel_register_count_lo and parallel_register_count_hi, for >> example), and increment the second one whenever the first one rolls >> over to zero. > > And that's going to be atomic how exactly? The only process that can look at that structure without taking a lock is the postmaster. And the postmaster would only examine parallel_register_count_lo. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company