On Tue, May 31, 2016 at 2:22 PM, Josh berkus <j...@agliodbs.com> wrote:
> On 05/31/2016 11:17 AM, Peter Eisentraut wrote: > > On 5/31/16 2:02 PM, Josh berkus wrote: > >> I get where you're coming from, but I think Haas's query plan output is > >> going to show us the confusion we're going to get. So we need to either > >> change the parameter, the explain output, or brace ourselves for endless > >> repeated questions. > > > > Changing the explain output doesn't sound so bad to me. > > > > The users' problem is that the parameter setting ought to match the > > EXPLAIN output. > > > > The developers' problem is that the EXPLAIN output actually corresponds > > to leader + (N-1) workers internally. > > > > I think we can hope that developers are going to be less confused about > > that than users. > > Makes sense. > > One more consistency question: what's the effect of running out of > max_parallel_workers? > > That is, say max_parallel_workers is set to 10, and 8 are already > allocated. If I ask for max_parallel_X = 4, how many cores to I use? > > Presumably the leader isn't counted towards max_parallel_workers? > You'd have three O/S processes - the one dedicated to your session and you'd pick up two additional processes from the worker pool to assist. How the O/S assigns those to cores is outside PostgreSQL's jurisdiction. David J.