Bug#44664: valgrind warning for COMMIT_AND_CHAIN and ROLLBACK_AND_CHAIN

The problem is that the internal variable used to specify a
transaction with consistent read was being used outside the
processing context of a START TRANSACTION WITH CONSISTENT
SNAPSHOT statement. The practical consequence was that a
consistent snapshot specification could leak to unrelated
transactions on the same session.

The solution is to ensure a consistent snapshot clause is
only relied upon for the START TRANSACTION statement.

This is already fixed in a similar way on 6.0.

mysql-test/r/consistent_snapshot.result:
  Add test case result for Bug#44664
mysql-test/t/consistent_snapshot.test:
  Add test case for Bug#44664
sql/sql_parse.cc:
  The WITH CONSISTENT SNAPSHOT clause is only valid for the
  START TRANSACTION statement.

mysql-test/r/consistent_snapshot.result

@@ -1,6 +1,9 @@
 DROP TABLE IF EXISTS t1;
 # Establish connection con1 (user=root)
 # Establish connection con2 (user=root)
+### Test 1:
+### - While a consistent snapshot transaction is executed,
+###   no external inserts should be visible to the transaction.
 # Switch to connection con1
 CREATE TABLE t1 (a INT) ENGINE=innodb;
 START TRANSACTION WITH CONSISTENT SNAPSHOT;
@@ -10,6 +13,9 @@ INSERT INTO t1 VALUES(1);
 SELECT * FROM t1;
 a
 COMMIT;
+### Test 2:
+### - For any non-consistent snapshot transaction, external
+###   committed inserts should be visible to the transaction.
 DELETE FROM t1;
 START TRANSACTION;
 # Switch to connection con2
@@ -19,5 +25,18 @@ SELECT * FROM t1;
 a
 1
 COMMIT;
+### Test 3:
+### - Bug#44664: valgrind warning for COMMIT_AND_CHAIN and ROLLBACK_AND_CHAIN
+###   Chaining a transaction does not retain consistency level.
+START TRANSACTION WITH CONSISTENT SNAPSHOT;
+DELETE FROM t1;
+COMMIT WORK AND CHAIN;
+# Switch to connection con2
+INSERT INTO t1 VALUES(1);
+# Switch to connection con1
+SELECT * FROM t1;
+a
+1
+COMMIT;
 # Switch to connection default + close connections con1 and con2
 DROP TABLE t1;

mysql-test/t/consistent_snapshot.test

@@ -12,9 +12,9 @@ connect (con1,localhost,root,,);
 --echo # Establish connection con2 (user=root)
 connect (con2,localhost,root,,);
 
-### Test 1:
+--echo ### Test 1:
-### - While a consistent snapshot transaction is executed,
+--echo ### - While a consistent snapshot transaction is executed,
-###   no external inserts should be visible to the transaction.
+--echo ###   no external inserts should be visible to the transaction.
 
 --echo # Switch to connection con1
 connection con1;
@@ -31,9 +31,9 @@ SELECT * FROM t1; # if consistent snapshot was set as expected, we
 # should see nothing.
 COMMIT;
 
-### Test 2:
+--echo ### Test 2:
-### - For any non-consistent snapshot transaction, external
+--echo ### - For any non-consistent snapshot transaction, external
-###   committed inserts should be visible to the transaction.
+--echo ###   committed inserts should be visible to the transaction.
 
 DELETE FROM t1;
 START TRANSACTION; # Now we omit WITH CONSISTENT SNAPSHOT
@@ -48,6 +48,24 @@ SELECT * FROM t1; # if consistent snapshot was not set, as expected, we
 # should see 1.
 COMMIT;
 
+--echo ### Test 3:
+--echo ### - Bug#44664: valgrind warning for COMMIT_AND_CHAIN and ROLLBACK_AND_CHAIN
+--echo ###   Chaining a transaction does not retain consistency level.
+
+START TRANSACTION WITH CONSISTENT SNAPSHOT;
+DELETE FROM t1;
+COMMIT WORK AND CHAIN;
+
+--echo # Switch to connection con2
+connection con2;
+INSERT INTO t1 VALUES(1);
+
+--echo # Switch to connection con1
+connection con1;
+SELECT * FROM t1; # if consistent snapshot was not set, as expected, we
+# should see 1.
+COMMIT;
+
 --echo # Switch to connection default + close connections con1 and con2
 connection default;
 disconnect con1;

sql/sql_parse.cc

@@ -198,8 +198,6 @@ bool begin_trans(THD *thd)
     LEX *lex= thd->lex;
     thd->options|= OPTION_BEGIN;
     thd->server_status|= SERVER_STATUS_IN_TRANS;
-    if (lex->start_transaction_opt & MYSQL_START_TRANS_OPT_WITH_CONS_SNAPSHOT)
-      error= ha_start_consistent_snapshot(thd);
   }
   return error;
 }
@@ -4027,6 +4025,11 @@ end_with_restore_list:
     }
     if (begin_trans(thd))
       goto error;
+    if (lex->start_transaction_opt & MYSQL_START_TRANS_OPT_WITH_CONS_SNAPSHOT)
+    {
+      if (ha_start_consistent_snapshot(thd))
+        goto error;
+    }
     my_ok(thd);
     break;
   case SQLCOM_COMMIT: