Fix assertion failure when Parallel Append is run serially.

Parallel-aware plan nodes must be prepared to run without parallelism
if it's not possible at execution time for whatever reason.  Commit
ab72716778128fb63d54ac256adf7fe6820a1185, which introduced Parallel
Append, overlooked this.

Rajkumar Raghuwanshi reported this problem, and I included his test
case in this patch.  The code changes are by me.

Discussion: http://postgr.es/m/CAKcux6=WqkUudLg1GLZZ7fc5ScWC1+Y9qD=pAHeqy32WoeJQvw@mail.gmail.com

diff --git a/src/backend/executor/nodeAppend.c b/src/backend/executor/nodeAppend.c
index 7a3dd2ee2d0495c1f2ec13c79512da20e61832c2..dcbf4d68aa494a397d06686a302e689f85fcf0fb 100644 (file)
--- a/src/backend/executor/nodeAppend.c
+++ b/src/backend/executor/nodeAppend.c
@@ -162,7 +162,7 @@ ExecInitAppend(Append *node, EState *estate, int eflags)
        appendstate->as_whichplan =
                appendstate->ps.plan->parallel_aware ? INVALID_SUBPLAN_INDEX : 0;
 
-       /* If parallel-aware, this will be overridden later. */
+       /* For parallel query, this will be overridden later. */
        appendstate->choose_next_subplan = choose_next_subplan_locally;
 
        return appendstate;
@@ -361,14 +361,21 @@ choose_next_subplan_locally(AppendState *node)
 {
        int                     whichplan = node->as_whichplan;
 
-       /* We should never see INVALID_SUBPLAN_INDEX in this case. */
-       Assert(whichplan >= 0 && whichplan <= node->as_nplans);
-
        if (ScanDirectionIsForward(node->ps.state->es_direction))
        {
-               if (whichplan >= node->as_nplans - 1)
-                       return false;
-               node->as_whichplan++;
+               /*
+                * We won't normally see INVALID_SUBPLAN_INDEX in this case, but we
+                * might if a plan intended to be run in parallel ends up being run
+                * serially.
+                */
+               if (whichplan == INVALID_SUBPLAN_INDEX)
+                       node->as_whichplan = 0;
+               else
+               {
+                       if (whichplan >= node->as_nplans - 1)
+                               return false;
+                       node->as_whichplan++;
+               }
        }
        else
        {

diff --git a/src/test/regress/expected/select_parallel.out b/src/test/regress/expected/select_parallel.out
index 452494fbfa3b134d8b2fabd1c4c4183b9cca8e7f..0a782616385a0fb868d3776fdc1f6867607e3347 100644 (file)
--- a/src/test/regress/expected/select_parallel.out
+++ b/src/test/regress/expected/select_parallel.out
@@ -121,6 +121,17 @@ select round(avg(aa)), sum(aa) from a_star a4;
 (1 row)
 
 reset enable_parallel_append;
+-- Parallel Append that runs serially
+create or replace function foobar() returns setof text as
+$$ select 'foo'::varchar union all select 'bar'::varchar $$
+language sql stable;
+select foobar() order by 1;
+ foobar 
+--------
+ bar
+ foo
+(2 rows)
+
 -- test with leader participation disabled
 set parallel_leader_participation = off;
 explain (costs off)

diff --git a/src/test/regress/sql/select_parallel.sql b/src/test/regress/sql/select_parallel.sql
index b12ba0b74a075f4380a8ded67a4c8865c52b88da..fa03aae0c03a1e105b874f0ae74e9c5538f64348 100644 (file)
--- a/src/test/regress/sql/select_parallel.sql
+++ b/src/test/regress/sql/select_parallel.sql
@@ -49,6 +49,12 @@ explain (costs off)
 select round(avg(aa)), sum(aa) from a_star a4;
 reset enable_parallel_append;
 
+-- Parallel Append that runs serially
+create or replace function foobar() returns setof text as
+$$ select 'foo'::varchar union all select 'bar'::varchar $$
+language sql stable;
+select foobar() order by 1;
+
 -- test with leader participation disabled
 set parallel_leader_participation = off;
 explain (costs off)