Allow parallel query for prepared statements with generic plans.

This was always intended to work, but due to an oversight in
max_parallel_hazard_walker, it didn't.  In testing, we missed the
fact that it was only working for custom plans, where the parameter
value has been substituted for the parameter itself early enough
that everything worked.  In a generic plan, the Param node survives
and must be treated as parallel-safe.  SerializeParamList provides
for the transmission of parameter values to workers.

Amit Kapila with help from Kuntal Ghosh.  Some changes by me.

Discussion: http://postgr.es/m/CAA4eK1+_BuZrmVCeua5Eqnm4Co9DAXdM5HPAOE2J19ePbR912Q@mail.gmail.com

diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 5344f6167a65a4a0fe69f3bfb8f33a1dd2d43fba..652843a146f76ab736161b0511ecc1996506fbe4 100644 (file)
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -1223,13 +1223,17 @@ max_parallel_hazard_walker(Node *node, max_parallel_hazard_context *context)
 
        /*
         * We can't pass Params to workers at the moment either, so they are also
-        * parallel-restricted, unless they are PARAM_EXEC Params listed in
-        * safe_param_ids, meaning they could be generated within the worker.
+        * parallel-restricted, unless they are PARAM_EXTERN Params or are
+        * PARAM_EXEC Params listed in safe_param_ids, meaning they could be
+        * generated within the worker.
         */
        else if (IsA(node, Param))
        {
                Param      *param = (Param *) node;
 
+               if (param->paramkind == PARAM_EXTERN)
+                       return false;
+
                if (param->paramkind != PARAM_EXEC ||
                        !list_member_int(context->safe_param_ids, param->paramid))
                {

diff --git a/src/pl/plpgsql/src/pl_exec.c b/src/pl/plpgsql/src/pl_exec.c
index 97166972594997492bc5c2971450743ba3f67f6d..e605ec829e3c424f32a3a52e738646c9788c88bf 100644 (file)
--- a/src/pl/plpgsql/src/pl_exec.c
+++ b/src/pl/plpgsql/src/pl_exec.c
@@ -6588,8 +6588,8 @@ exec_save_simple_expr(PLpgSQL_expr *expr, CachedPlan *cplan)
         * force_parallel_mode is on, the planner might've stuck a Gather node
         * atop that.  The simplest way to deal with this is to look through the
         * Gather node.  The Gather node's tlist would normally contain a Var
-        * referencing the child node's output ... but setrefs.c might also have
-        * copied a Const as-is.
+        * referencing the child node's output, but it could also be a Param, or
+        * it could be a Const that setrefs.c copied as-is.
         */
        plan = stmt->planTree;
        for (;;)
@@ -6616,9 +6616,9 @@ exec_save_simple_expr(PLpgSQL_expr *expr, CachedPlan *cplan)
                        /* If setrefs.c copied up a Const, no need to look further */
                        if (IsA(tle_expr, Const))
                                break;
-                       /* Otherwise, it better be an outer Var */
-                       Assert(IsA(tle_expr, Var));
-                       Assert(((Var *) tle_expr)->varno == OUTER_VAR);
+                       /* Otherwise, it had better be a Param or an outer Var */
+                       Assert(IsA(tle_expr, Param) || (IsA(tle_expr, Var) &&
+                                       ((Var *) tle_expr)->varno == OUTER_VAR));
                        /* Descend to the child node */
                        plan = plan->lefttree;
                }

diff --git a/src/test/regress/expected/select_parallel.out b/src/test/regress/expected/select_parallel.out
index 2ae600f1bbbd130903df860c71fa06947b2e82ec..3c63ad1de86976fd96d23264b304d438a3e736e0 100644 (file)
--- a/src/test/regress/expected/select_parallel.out
+++ b/src/test/regress/expected/select_parallel.out
@@ -101,6 +101,26 @@ explain (costs off)
          ->  Parallel Index Only Scan using tenk1_unique1 on tenk1
 (5 rows)
 
+-- test prepared statement
+prepare tenk1_count(integer) As select  count((unique1)) from tenk1 where hundred > $1;
+explain (costs off) execute tenk1_count(1);
+                  QUERY PLAN                  
+----------------------------------------------
+ Finalize Aggregate
+   ->  Gather
+         Workers Planned: 4
+         ->  Partial Aggregate
+               ->  Parallel Seq Scan on tenk1
+                     Filter: (hundred > 1)
+(6 rows)
+
+execute tenk1_count(1);
+ count 
+-------
+  9800
+(1 row)
+
+deallocate tenk1_count;
 -- test parallel plans for queries containing un-correlated subplans.
 alter table tenk2 set (parallel_workers = 0);
 explain (costs off)

diff --git a/src/test/regress/sql/select_parallel.sql b/src/test/regress/sql/select_parallel.sql
index 89fe80a35c296d7946e95a5371d74169c0520080..720495c81173982a309729c4928197ef1346befd 100644 (file)
--- a/src/test/regress/sql/select_parallel.sql
+++ b/src/test/regress/sql/select_parallel.sql
@@ -39,6 +39,12 @@ explain (costs off)
        select  sum(parallel_restricted(unique1)) from tenk1
        group by(parallel_restricted(unique1));
 
+-- test prepared statement
+prepare tenk1_count(integer) As select  count((unique1)) from tenk1 where hundred > $1;
+explain (costs off) execute tenk1_count(1);
+execute tenk1_count(1);
+deallocate tenk1_count;
+
 -- test parallel plans for queries containing un-correlated subplans.
 alter table tenk2 set (parallel_workers = 0);
 explain (costs off)