Fix CTAS crash.

If we create a replicated table when selecting project volatile
functions from a randomly distributed table, we will try to add
a Motion on a Motion node that will cause a crash.
Create table t1(id int) distributed randomly;
Create table t2 as select random() from t1 distributed replicated;

planner may have add a top Motion earlier if we know the query's
final locus. Some codes handle volatile functions lead us to
create_motion_path_for_insert(), and we should consider the case
to avoid Assertion failure when create_plan().

Authored-by: Zhang Mingli avamingli@gmail.com

Author: avamingli

src/backend/cdb/cdbpath.c

@@ -2622,7 +2622,15 @@ create_motion_path_for_insert(PlannerInfo *root, GpPolicy *policy,
 			}
 
 		}
-		subpath = cdbpath_create_broadcast_motion_path(root, subpath, policy->numsegments);
+
+		/*
+		 * planner may have add a top Motion eariler.
+		 * Create table t1(id int) distributed randomly;
+		 * Create table t2 as select random() from t1 distributed replicated;
+		 * Avoid Motion if there was already one.
+		 */
+		if (!CdbPathLocus_IsReplicated(subpath->locus))
+			subpath = cdbpath_create_broadcast_motion_path(root, subpath, policy->numsegments);
 	}
 	else
 		elog(ERROR, "unrecognized policy type %u", policyType);

src/test/regress/expected/bfv_planner.out

@@ -663,6 +663,8 @@ select count(distinct nextval) from gp_dist_random('t_rep4');
 (1 row)
 
 drop table rep_tbl, t_rep4;
+create table t_issue_1218_random(id int) distributed randomly;
+create table t_issue_1218_replicated as select random() from t_issue_1218_random distributed replicated;
 --
 -- Test append different numsegments tables work well
 -- See Github issue: https://github.com/greenplum-db/gpdb/issues/12146

src/test/regress/expected/bfv_planner_optimizer.out

@@ -681,6 +681,8 @@ select count(distinct nextval) from gp_dist_random('t_rep4');
 (1 row)
 
 drop table rep_tbl, t_rep4;
+create table t_issue_1218_random(id int) distributed randomly;
+create table t_issue_1218_replicated as select random() from t_issue_1218_random distributed replicated;
 --
 -- Test append different numsegments tables work well
 -- See Github issue: https://github.com/greenplum-db/gpdb/issues/12146

src/test/regress/sql/bfv_planner.sql

@@ -345,6 +345,9 @@ select count(*) from gp_dist_random('t_rep4');
 select count(distinct nextval) from gp_dist_random('t_rep4');
 drop table rep_tbl, t_rep4;
 
+create table t_issue_1218_random(id int) distributed randomly;
+create table t_issue_1218_replicated as select random() from t_issue_1218_random distributed replicated;
+
 --
 -- Test append different numsegments tables work well
 -- See Github issue: https://github.com/greenplum-db/gpdb/issues/12146