On 30 September 2016 at 10:47, Jay Knight <jay@xxxxxxxxxxxxx> wrote: >>What's max_worker_processes set to? > > 8 > >>One theory would be that, the worker might not have been available >>when you performed the query execution, but it just happened to be >>when you did the EXPLAIN ANALYZE > > This happens consistently this way. Every time I run it with explain > analyze it uses parallel workers, and every time I run it without it > doesn't. I just enabled auto_explain, and see that it is "planning" to use > a worker, but doesn't launch it. Is there a way to know why a planned > worker doesn't get launched? It seems not, at least not unless you're willing to attach a debugger. > 2016-09-29 16:45:44 CDT LOG: duration: 50703.595 ms plan: > Query Text: select count(*) from t1 > join t2 on t1.item = t2.item and t1.low <= t2.high and t1.high >= t2.low > Finalize Aggregate (cost=14609058.99..14609059.00 rows=1 width=8) > (actual time=50703.584..50703.584 rows=1 loops=1) > -> Gather (cost=14609058.88..14609058.99 rows=1 width=8) (actual > time=50703.581..50703.581 rows=1 loops=1) > Workers Planned: 1 > Workers Launched: 0 > -> Partial Aggregate (cost=14608958.88..14608958.89 rows=1 > width=8) (actual time=50703.579..50703.579 rows=1 loops=1) > -> Nested Loop (cost=0.42..13608937.28 rows=400008641 > width=0) (actual time=0.534..50577.673 rows=3669891 loops=1) > -> Parallel Seq Scan on t1 (cost=0.00..3386.71 > rows=176471 width=12) (actual time=0.041..18.351 rows=300000 loops=1) > -> Index Only Scan using t2_item_low_high_idx on t2 > (cost=0.42..63.77 rows=1333 width=12) (actual time=0.167..0.168 rows=12 > loops=300000) > Index Cond: ((item = t1.item) AND (low <= > t1.high) AND (high >= t1.low)) > Heap Fetches: 0 That's interesting. How about trying to increase max_worker_processes to say, 16. I know you've said you've tried multiple times and it seems consistent, but increasing this seems to be worth a try, if anything, to rule that out. -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
