Update autocommit mode and transaction state

The transaction state only reflects explicitly started transactions.
Thus, by looking at the autocommit mode and the transaction state a
component can figure out whether the current statement will be committed
or not.

include/maxscale/session.h

@@ -83,8 +83,6 @@ typedef enum
 
 typedef enum
 {
-    /*< The current transaction state is not known. */
-    SESSION_TRX_UNKNOWN     = 0,
     /*< There is no on-going transaction. */
     SESSION_TRX_INACTIVE    = SESSION_TRX_INACTIVE_BIT,
     /*< A transaction is active. */
@@ -241,6 +239,20 @@ void enable_session_timeouts();
 /**
  * Get the transaction state of the session.
  *
+ * Note that this tells only the state of @e explicitly started transactions.
+ * That is, if @e autocommit is OFF, which means that there is always an
+ * active transaction that is ended with an explicit COMMIT or ROLLBACK,
+ * at which point a new transaction is started, this function will still
+ * return SESSION_TRX_INACTIVE, unless a transaction has explicitly been
+ * started with START TRANSACTION.
+ *
+ * Likewise, if @e autocommit is ON, which means that every statement is
+ * executed in a transaction of its own, this will return false, unless a
+ * transaction has explicitly been started with START TRANSACTION.
+ *
+ * @note The return value is valid only if either a router or a filter
+ *       has declared that it needs RCAP_TYPE_TRANSACTION_TRACKING.
+ *
  * @param ses The SESSION object.
  * @return The transaction state.
  */
@@ -259,7 +271,12 @@ session_trx_state_t session_get_trx_state(const SESSION* ses);
 session_trx_state_t session_set_trx_state(SESSION* ses, session_trx_state_t new_state);
 
 /**
- * Tells whether a transaction is active.
+ * Tells whether an explicit transaction is active.
+ *
+ * @see session_get_trx_state
+ *
+ * @note The return value is valid only if either a router or a filter
+ *       has declared that it needs RCAP_TYPE_TRANSACTION_TRACKING.
  *
  * @return True if a transaction is active, false otherwise.
  */
@@ -271,6 +288,11 @@ static inline bool session_trx_is_active(const SESSION* ses)
 /**
  * Tells whether an explicit READ ONLY transaction is active.
  *
+ * @see session_get_trx_state
+ *
+ * @note The return value is valid only if either a router or a filter
+ *       has declared that it needs RCAP_TYPE_TRANSACTION_TRACKING.
+ *
  * @return True if an explicit READ ONLY transaction is active,
  *         false otherwise.
  */
@@ -282,6 +304,11 @@ static inline bool session_trx_is_read_only(const SESSION* ses)
 /**
  * Tells whether an explicit READ WRITE transaction is active.
  *
+ * @see session_get_trx_state
+ *
+ * @note The return value is valid only if either a router or a filter
+ *       has declared that it needs RCAP_TYPE_TRANSACTION_TRACKING.
+ *
  * @return True if an explicit READ WRITE  transaction is active,
  *         false otherwise.
  */
@@ -303,6 +330,8 @@ static inline bool session_trx_is_read_write(const SESSION* ses)
  *
  * Note also that by default autocommit is ON.
  *
+ * @see session_get_trx_state
+ *
  * @return True if autocommit has been set ON, false otherwise.
  */
 static inline bool session_is_autocommit(const SESSION* ses)

server/core/session.c

@@ -142,7 +142,7 @@ session_alloc(SERVICE *service, DCB *client_dcb)
      */
     session->state = SESSION_STATE_READY;
 
-    session->trx_state = SESSION_TRX_UNKNOWN;
+    session->trx_state = SESSION_TRX_INACTIVE;
     session->autocommit = true;
     /*
      * Only create a router session if we are not the listening
@@ -1081,8 +1081,6 @@ const char* session_trx_state_to_string(session_trx_state_t state)
 {
     switch (state)
     {
-    case SESSION_TRX_UNKNOWN:
-        return "SESSION_TRX_UNKNOWN";
     case SESSION_TRX_INACTIVE:
         return "SESSION_TRX_INACTIVE";
     case SESSION_TRX_ACTIVE:

server/modules/protocol/MySQL/MySQLClient/mysql_client.c

@@ -1439,25 +1439,28 @@ static int route_by_statement(SESSION* session, uint64_t capabilities, GWBUF** p
 
                     if (type & QUERY_TYPE_BEGIN_TRX)
                     {
-                        session_trx_state_t trx_state;
-                        if (type & QUERY_TYPE_WRITE)
-                        {
-                            trx_state = SESSION_TRX_READ_WRITE;
-                        }
-                        else if (type & QUERY_TYPE_READ)
-                        {
-                            trx_state = SESSION_TRX_READ_ONLY;
-                        }
-                        else
-                        {
-                            trx_state = SESSION_TRX_ACTIVE;
-                        }
-
-                        session_set_trx_state(session, trx_state);
-
                         if (type & QUERY_TYPE_DISABLE_AUTOCOMMIT)
                         {
                             session_set_autocommit(session, false);
+                            session_set_trx_state(session, SESSION_TRX_INACTIVE);
+                        }
+                        else
+                        {
+                            session_trx_state_t trx_state;
+                            if (type & QUERY_TYPE_WRITE)
+                            {
+                                trx_state = SESSION_TRX_READ_WRITE;
+                            }
+                            else if (type & QUERY_TYPE_READ)
+                            {
+                                trx_state = SESSION_TRX_READ_ONLY;
+                            }
+                            else
+                            {
+                                trx_state = SESSION_TRX_ACTIVE;
+                            }
+
+                            session_set_trx_state(session, trx_state);
                         }
                     }
                     else if ((type & QUERY_TYPE_COMMIT) || (type & QUERY_TYPE_ROLLBACK))