Fix to bug 736: http://bugs.mariadb.com/show_bug.cgi?id=736

Added a cofigurable limit on the number of session commands the readwritesplit router stores.

Documentation/Getting-Started/Configuration-Guide.md

@@ -798,6 +798,12 @@ When value all is used, queries reading session variables can be routed to any a
 
 In above-mentioned case the user-defined variable would only be updated in the master where query would be routed due to `INSERT` statement.
 
+`max_sescmd_history` sets a limit on how many session commands each session can execute before the connection is closed. The default is an unlimited number of session commands.
+
+	max_sescmd_history=1500
+
+When a limitation is set, it effectively creates a cap on the session's memory consumption. This might be useful if connection pooling is used and the sessions use large amounts of session commands.
+
 An example of Read/Write Split router configuration :
 
 ```

server/MaxScale_template.cnf

@@ -182,6 +182,12 @@ replace=select
 #	router_options=
 #	slave_selection_criteria=[LEAST_CURRENT_OPERATIONS|LEAST_BEHIND_MASTER]
 #
+# router_options=max_sescmd_history specifies a limit on the number of 'session commands'
+# a single session can execute. Please refer to the configuration guide for more details - optional.
+#
+#	router_options=
+#	max_sescmd_history=2500
+#
 # max_slave_connections specifies how many slaves a router session can 
 # connect to - optional.
 #

server/modules/include/readwritesplit.h

@@ -246,7 +246,8 @@ typedef struct rwsplit_config_st {
         int               rw_max_slave_conn_count;
         select_criteria_t rw_slave_select_criteria;
         int               rw_max_slave_replication_lag;
-	target_t          rw_use_sql_variables_in;	
+	target_t          rw_use_sql_variables_in;
+        int               rw_max_sescmd_history_size;
 } rwsplit_config_t;
      
 
@@ -285,6 +286,7 @@ struct router_client_session {
         backend_ref_t*   rses_backend_ref; /*< Pointer to backend reference array */
         rwsplit_config_t rses_config;    /*< copied config info from router instance */
         int              rses_nbackends;
+        int              rses_nsescmd;  /*< Number of executed session commands */
         int              rses_capabilities; /*< input type, for example */
         bool             rses_autocommit_enabled;
         bool             rses_transaction_active;

server/modules/routing/readwritesplit/readwritesplit.c

@@ -4347,6 +4347,19 @@ static bool route_session_write(
 		
 		goto return_succp;
 	}
+
+	if(router_cli_ses->rses_config.rw_max_sescmd_history_size > 0 &&
+	 router_cli_ses->rses_nsescmd >= router_cli_ses->rses_config.rw_max_sescmd_history_size)
+	{
+	    LOGIF(LT, (skygw_log_write(
+		    LOGFILE_TRACE,
+			"Router session exceeded session command history limit. "
+		        "Closing router session. <")));
+		router_cli_ses->rses_closed = true;
+		rses_end_locked_router_action(router_cli_ses);
+		goto return_succp;
+	}
+
         /** 
          * Additional reference is created to querybuf to 
          * prevent it from being released before properties
@@ -4418,6 +4431,9 @@ static bool route_session_write(
                         }
                 }
         }
+
+	atomic_add(&router_cli_ses->rses_nsescmd,1);
+
         /** Unlock router session */
         rses_end_locked_router_action(router_cli_ses);
                
@@ -4517,6 +4533,10 @@ static void rwsplit_process_router_options(
                                         router->rwsplit_config.rw_slave_select_criteria = c;
                                 }
                         }
+			else if(strcmp(options[i], "max_sescmd_history") == 0)
+			{
+			    router->rwsplit_config.rw_max_sescmd_history_size = atoi(value);
+			}
                 }
         } /*< for */
 }