Regression when PARALLELISM kicks in

[robe]

So I forced parallelism on on my PostgreSQL 9.6 instance with this:

ALTER SYSTEM set parallel_tuple_cost=0.01;
ALTER SYSTEM set max_parallel_degree=4;
ALTER SYSTEM set force_parallel_mode=on;
ALTER SYSTEM set parallel_setup_cost=100;

SELECT pg_reload_conf();

and after that I get two regression failures:

regress_index .. failed (diff expected obtained: /projects/postgis/tmp/2.3_pg9.6w64/test_59_diff)

sfcgal/regress_ogc_prep .. failed (diff expected obtained: /projects/postgis/tmp/2.3_pg9.6w64/test_119_diff)

The first one I forget what all those things mean so might be just the way parallelism is breaking out the work load:

--- regress_index_expected	2015-07-30 14:50:49 -0400
+++ /projects/postgis/tmp/2.3_pg9.6w64/test_59_out	2016-05-16 21:28:41 -0400
@@ -7,10 +7,10 @@
 3618|POINT(130.447205 131.655289)
 7245|POINT(128.10466 130.94133)
 3+=5:true
-924+=60:true
-12621+=500:true
-50000+=600:true
+924+=60:false:924
+12621+=500:false:12621
+50000+=600:false:50000
 expr|3+=5:true
-expr|924+=60:true
-expr|12621+=500:true
-expr|50000+=600:true
+expr|924+=60:false:924
+expr|12621+=500:false:12621
+expr|50000+=600:false:50000

The sfcgal one I guess means we can't have parallelism enabled for all tests, have to be selective, which means our regress needs to be modified to accomodate parallel testing (I'll flag as separate ticket).

--- sfcgal/regress_ogc_prep_expected	2015-07-30 14:50:46 -0400
+++ /projects/postgis/tmp/2.3_pg9.6w64/test_119_out	2016-05-16 21:29:44 -0400
@@ -1,21 +1,25 @@
+WARNING:  cannot set parameters during a parallel operation
 intersects099|t
 intersects100|t
 intersects101|t
 intersects102|f
 intersects103|t
 intersects104|f
+WARNING:  cannot set parameters during a parallel operation
 contains099|t
 contains100|t
 contains101|f
 contains102|f
 contains103|f
 contains104|f
+WARNING:  cannot set parameters during a parallel operation
 covers099|t
 covers100|t
 covers101|t
 covers102|f
 covers103|t
 covers104|f
+WARNING:  cannot set parameters during a parallel operation
 containsproperly099|t
 containsproperly100|t
 containsproperly101|f

[pramsey]

I ran this test against trunk (no CGAL tho) w/o issue. Since you have to work to create a failure mode, I'm going to close as worksforme and we'll wait for a real bug to fix.