MDEV-35571 Check for LIMIT ROWS EXAMINED exceeded in UNION ALL

When UNION ALL is used with LIMIT ROWS EXAMINED, and when the limit is
exceeded for a SELECT that is not the last in the UNION, interrupt the
execution and call end_eof on the result. This makes sure that the
results are sent, and the query result status is conclusive rather
than empty, which would cause an assertion failure.

mysql-test/main/limit_rows_examined.result

@@ -895,3 +895,46 @@ Warnings:
 Note	1003	select `test`.`t1`.`c1` AS `c1`,`test`.`t2`.`c2` AS `c2` from `test`.`t1` join `test`.`t2` where `test`.`t2`.`c2` = `test`.`t1`.`c1`
 drop table t1,t2;
 # End of 10.4 tests
+#
+# MDEV-35571: Connection hangs after query on a partitioned table with UNION and LIMIT ROWS EXAMINED
+#
+create table t1 (a int);
+insert into t1 values (1), (2);
+select * from t1 UNION ALL select * from t1 LIMIT ROWS EXAMINED 1;
+a
+1
+Warnings:
+Warning	1931	Query execution was interrupted. The query exceeded LIMIT ROWS EXAMINED 1. The query result may be incomplete
+select * from t1 UNION DISTINCT select * from t1 LIMIT ROWS EXAMINED 1;
+a
+1
+Warnings:
+Warning	1931	Query execution was interrupted. The query exceeded LIMIT ROWS EXAMINED 1. The query result may be incomplete
+DROP TABLE t1;
+create table t1 (a int);
+insert into t1 values (1), (2);
+(select a from t1 UNION ALL select a from t1) order by a desc LIMIT ROWS EXAMINED 2;
+a
+1
+Warnings:
+Warning	1931	Query execution was interrupted. The query exceeded LIMIT ROWS EXAMINED 2. The query result may be incomplete
+(select a from t1 UNION DISTINCT select a from t1) order by a desc LIMIT ROWS EXAMINED 2;
+a
+1
+Warnings:
+Warning	1931	Query execution was interrupted. The query exceeded LIMIT ROWS EXAMINED 2. The query result may be incomplete
+DROP TABLE t1;
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 SELECT seq%25 FROM seq_1_to_100;
+CREATE TABLE t2 (b INT, c INT, KEY(b)) PARTITION BY HASH(c) PARTITIONS 12;
+INSERT INTO t2 SELECT seq, seq FROM seq_1_to_10;
+SELECT COUNT(*) FROM t1 JOIN t2 ON (b = a) UNION ALL SELECT COUNT(*) FROM t1 JOIN t2 ON (b = a) LIMIT ROWS EXAMINED 100;
+COUNT(*)
+Warnings:
+Warning	1931	Query execution was interrupted. The query exceeded LIMIT ROWS EXAMINED 100. The query result may be incomplete
+SELECT COUNT(*) FROM t1 JOIN t2 ON (b = a) UNION DISTINCT SELECT COUNT(*) FROM t1 JOIN t2 ON (b = a) LIMIT ROWS EXAMINED 100;
+COUNT(*)
+Warnings:
+Warning	1931	Query execution was interrupted. The query exceeded LIMIT ROWS EXAMINED 100. The query result may be incomplete
+DROP TABLE t1, t2;
+# End of 10.5 tests

mysql-test/main/limit_rows_examined.test

@@ -617,3 +617,44 @@ select * from t1, t2 where c1 = c2 LIMIT ROWS EXAMINED 2;
 drop table t1,t2;
 
 --echo # End of 10.4 tests
+
+--echo #
+--echo # MDEV-35571: Connection hangs after query on a partitioned table with UNION and LIMIT ROWS EXAMINED
+--echo #
+
+--source include/have_partition.inc
+--source include/have_sequence.inc
+
+# Simplified test
+create table t1 (a int);
+insert into t1 values (1), (2);
+select * from t1 UNION ALL select * from t1 LIMIT ROWS EXAMINED 1;
+# UNION DISTINCT produces the same result here. Note that this is not
+# affected by the MDEV-35571 patch
+select * from t1 UNION DISTINCT select * from t1 LIMIT ROWS EXAMINED 1;
+DROP TABLE t1;
+
+# Simplified test with order by
+create table t1 (a int);
+insert into t1 values (1), (2);
+(select a from t1 UNION ALL select a from t1) order by a desc LIMIT ROWS EXAMINED 2;
+# UNION DISTINCT produces the same result with order by desc. Note
+# that this is not affected by the MDEV-35571 patch
+(select a from t1 UNION DISTINCT select a from t1) order by a desc LIMIT ROWS EXAMINED 2;
+DROP TABLE t1;
+
+# Original test
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 SELECT seq%25 FROM seq_1_to_100;
+
+CREATE TABLE t2 (b INT, c INT, KEY(b)) PARTITION BY HASH(c) PARTITIONS 12;
+INSERT INTO t2 SELECT seq, seq FROM seq_1_to_10;
+
+SELECT COUNT(*) FROM t1 JOIN t2 ON (b = a) UNION ALL SELECT COUNT(*) FROM t1 JOIN t2 ON (b = a) LIMIT ROWS EXAMINED 100;
+# UNION DISTINCT produces the same result here. Note that this is not
+# affected by the MDEV-35571 patch
+SELECT COUNT(*) FROM t1 JOIN t2 ON (b = a) UNION DISTINCT SELECT COUNT(*) FROM t1 JOIN t2 ON (b = a) LIMIT ROWS EXAMINED 100;
+
+DROP TABLE t1, t2;
+
+--echo # End of 10.5 tests

sql/sql_union.cc

@@ -1026,7 +1026,8 @@ bool select_union_direct::send_eof()
   // Reset for each SELECT_LEX, so accumulate here
   limit_found_rows+= thd->limit_found_rows;
 
-  if (unit->thd->lex->current_select == last_select_lex)
+  if (unit->thd->lex->current_select == last_select_lex ||
+      thd->killed == ABORT_QUERY)
   {
     thd->limit_found_rows= limit_found_rows;