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 8b4425dcf90ddd5762bd2881c262b059b683c2e8..fa53b7a8c5050c579fa27d79340a6d9374a8e1f5 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 c98492b2a42484fdd7ce256cf5c2947cadb79258..d4333b6dc27ab20f84dd022a62a5c9af6917f0f5 100644 (file)
--- a/src/pl/plpgsql/src/pl_exec.c
+++ b/src/pl/plpgsql/src/pl_exec.c
@@ -6821,7 +6821,7 @@ exec_simple_recheck_plan(PLpgSQL_expr *expr, CachedPlan *cplan)
 {
        PlannedStmt *stmt;
        Plan       *plan;
-       TargetEntry *tle;
+       Expr       *tle_expr;
 
        /*
         * Initialize to "not simple", and remember the plan generation number we
@@ -6836,18 +6836,51 @@ exec_simple_recheck_plan(PLpgSQL_expr *expr, CachedPlan *cplan)
        if (list_length(cplan->stmt_list) != 1)
                return;
        stmt = linitial_node(PlannedStmt, cplan->stmt_list);
+       if (stmt->commandType != CMD_SELECT)
+               return;
 
        /*
-        * 2. It must be a RESULT plan --> no scan's required
+        * 2. Ordinarily, the plan node should be a simple Result.  However, if
+        * 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 it could also be a Param, or
+        * it could be a Const that setrefs.c copied as-is.
         */
-       if (stmt->commandType != CMD_SELECT)
-               return;
        plan = stmt->planTree;
-       if (!IsA(plan, Result))
-               return;
+       for (;;)
+       {
+               /*
+                * 3. The plan must have a single attribute as result
+                */
+               if (list_length(plan->targetlist) != 1)
+                       return;
+               tle_expr = castNode(TargetEntry, linitial(plan->targetlist))->expr;
+
+               if (IsA(plan, Gather))
+               {
+                       if (plan->righttree != NULL ||
+                               plan->initPlan != NULL ||
+                               plan->qual != NULL)
+                               return;
+                       /* If setrefs.c copied up a Const, no need to look further */
+                       if (IsA(tle_expr, Const))
+                               break;
+                       /* Otherwise, it had better be a Param or an outer Var */
+                       if (!IsA(tle_expr, Param) && !(IsA(tle_expr, Var) &&
+                                       ((Var *) tle_expr)->varno == OUTER_VAR))
+                               return;
+                       /* Descend to the child node */
+                       plan = plan->lefttree;
+                       continue;
+               }
+               else if (!IsA(plan, Result))
+                       return;
+               break;
+       }
 
        /*
-        * 3. Can't have any subplan or qual clause, either
+        * 4. Can't have any subplan or qual clause, either
         */
        if (plan->lefttree != NULL ||
                plan->righttree != NULL ||
@@ -6856,31 +6889,23 @@ exec_simple_recheck_plan(PLpgSQL_expr *expr, CachedPlan *cplan)
                ((Result *) plan)->resconstantqual != NULL)
                return;
 
-       /*
-        * 4. The plan must have a single attribute as result
-        */
-       if (list_length(plan->targetlist) != 1)
-               return;
-
-       tle = (TargetEntry *) linitial(plan->targetlist);
-
        /*
         * 5. Check that all the nodes in the expression are non-scary.
         */
-       if (!exec_simple_check_node((Node *) tle->expr))
+       if (!exec_simple_check_node((Node *) tle_expr))
                return;
 
        /*
         * Yes - this is a simple expression.  Mark it as such, and initialize
         * state to "not valid in current transaction".
         */
-       expr->expr_simple_expr = tle->expr;
+       expr->expr_simple_expr = tle_expr;
        expr->expr_simple_state = NULL;
        expr->expr_simple_in_use = false;
        expr->expr_simple_lxid = InvalidLocalTransactionId;
        /* Also stash away the expression result type */
-       expr->expr_simple_type = exprType((Node *) tle->expr);
-       expr->expr_simple_typmod = exprTypmod((Node *) tle->expr);
+       expr->expr_simple_type = exprType((Node *) tle_expr);
+       expr->expr_simple_typmod = exprTypmod((Node *) tle_expr);
 }
 
 /*

diff --git a/src/test/regress/expected/select_parallel.out b/src/test/regress/expected/select_parallel.out
index 6bbcd34b800e0cc76f14f028bdd0de0eafe4ccd8..f3e8b565871b62f852160df1be772dd89709f66f 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 cf02d84c8d8fa198f69be53ef09710b3619a690c..d2eee147e99e55d8c36e37e79de78dcbb8ef677a 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)