1 files changed, 50 insertions, 5 deletions

diff --git a/sql/sql_class.h b/sql/sql_class.h
index 0a098fc8492..ac1a10f57b9 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -2309,10 +2309,6 @@ public:
   {
     return limit_found_rows;
   }
-  inline bool active_transaction()
-  {
-    return server_status & SERVER_STATUS_IN_TRANS;
-  }
   /**
     Returns TRUE if session is in a multi-statement transaction mode.
 
@@ -2323,11 +2319,60 @@ public:
     OPTION_BEGIN: Regardless of the autocommit status, a multi-statement
     transaction can be explicitly started with the statements "START
     TRANSACTION", "BEGIN [WORK]", "[COMMIT | ROLLBACK] AND CHAIN", etc.
+
+    Note: this doesn't tell you whether a transaction is active.
+    A session can be in multi-statement transaction mode, and yet
+    have no active transaction, e.g., in case of:
+    set @@autocommit=0;
+    set @a= 3;                                     <-- these statements don't
+    set transaction isolation level serializable;  <-- start an active
+    flush tables;                                  <-- transaction
+
+    I.e. for the above scenario this function returns TRUE, even
+    though no active transaction has begun.
+    @sa in_active_multi_stmt_transaction()
   */
-  inline bool in_multi_stmt_transaction()
+  inline bool in_multi_stmt_transaction_mode()
   {
     return variables.option_bits & (OPTION_NOT_AUTOCOMMIT | OPTION_BEGIN);
   }
+  /**
+    TRUE if the session is in a multi-statement transaction mode
+    (@sa in_multi_stmt_transaction_mode()) *and* there is an
+    active transaction, i.e. there is an explicit start of a
+    transaction with BEGIN statement, or implicit with a
+    statement that uses a transactional engine.
+
+    For example, these scenarios don't start an active transaction
+    (even though the server is in multi-statement transaction mode):
+
+    set @@autocommit=0;
+    select * from nontrans_table;
+    set @var=TRUE;
+    flush tables;
+
+    Note, that even for a statement that starts a multi-statement
+    transaction (i.e. select * from trans_table), this
+    flag won't be set until we open the statement's tables
+    and the engines register themselves for the transaction
+    (see trans_register_ha()),
+    hence this method is reliable to use only after
+    open_tables() has completed.
+
+    Why do we need a flag?
+    ----------------------
+    We need to maintain a (at first glance redundant)
+    session flag, rather than looking at thd->transaction.all.ha_list
+    because of explicit start of a transaction with BEGIN. 
+
+    I.e. in case of
+    BEGIN;
+    select * from nontrans_t1; <-- in_active_multi_stmt_transaction() is true
+  */
+  inline bool in_active_multi_stmt_transaction()
+  {
+    return server_status & SERVER_STATUS_IN_TRANS;
+  }
   inline bool fill_derived_tables()
   {
     return !stmt_arena->is_stmt_prepare() && !lex->only_view_structure();