1 files changed, 29 insertions, 0 deletions
diff --git a/sql/handler.h b/sql/handler.h
index a3767573178..c44d7c7f846 100644
--- a/sql/handler.h
+++ b/sql/handler.h
@@ -420,6 +420,35 @@ typedef struct st_thd_trans
   bool        no_2pc;
   /* storage engines that registered themselves for this transaction */
   handlerton *ht[MAX_HA];
+  /* 
+    The purpose of this flag is to keep track of non-transactional
+    tables that were modified in scope of:
+    - transaction, when the variable is a member of
+    THD::transaction.all
+    - top-level statement or sub-statement, when the variable is a
+    member of THD::transaction.stmt
+    This member has the following life cycle:
+    * stmt.modified_non_trans_table is used to keep track of
+    modified non-transactional tables of top-level statements. At
+    the end of the previous statement and at the beginning of the session,
+    it is reset to FALSE.  If such functions
+    as mysql_insert, mysql_update, mysql_delete etc modify a
+    non-transactional table, they set this flag to TRUE.  At the
+    end of the statement, the value of stmt.modified_non_trans_table 
+    is merged with all.modified_non_trans_table and gets reset.
+    * all.modified_non_trans_table is reset at the end of transaction
+    
+    * Since we do not have a dedicated context for execution of a
+    sub-statement, to keep track of non-transactional changes in a
+    sub-statement, we re-use stmt.modified_non_trans_table. 
+    At entrance into a sub-statement, a copy of the value of
+    stmt.modified_non_trans_table (containing the changes of the
+    outer statement) is saved on stack. Then 
+    stmt.modified_non_trans_table is reset to FALSE and the
+    substatement is executed. Then the new value is merged with the
+    saved value.
+  */
+  bool modified_non_trans_table;
 } THD_TRANS;
 
 enum enum_tx_isolation { ISO_READ_UNCOMMITTED, ISO_READ_COMMITTED,