Change strict_multi_stmt default value

The default value for strict_multi_stmt prevents compound statements and
atomic multi-statement commands from being executed without completely
disabling load balancing. As the new default value will have no practical
effect on all correct uses of readwritesplit, this is a relatively safe
thing to change.

Documentation/Release-Notes/MaxScale-2.2.1-Release-Notes.md

@@ -50,6 +50,21 @@ root@host:~# maxscale --user=root ...
 The default value of the configuration parameter `detect_standalone_master` has
 been changed from `false` to `true`.
 
+### ReadWritesplit
+
+The default value of `strict_multi_stmt` was changed to `false` to make
+usage of atomic compound statements and multi-statement queries less
+restrictive and to align it with the default value of `strict_sp_calls`.
+
+Most cases where the functionality of `strict_multi_stmt` was triggered
+were cases where the added safety of locking a session to the master did
+more harm than it did good.
+
+The only case where `strict_multi_stmt` should be enabled is when a
+multi-statement or a compound statement modifies the state of the
+session. This is not a good practice and a change in the client side
+behavior is advised.
+
 ## Dropped Features
 
 ## New Features

Documentation/Routers/ReadWriteSplit.md

@@ -220,21 +220,23 @@ router_options=master_accept_reads=true
 
 ### `strict_multi_stmt`
 
-When a client executes a multi-statement query, all queries after that will be
+This option is disabled by default since MaxScale 2.2.1. In older versions, this
-routed to the master to guarantee a consistent session state. This behavior can
+option was enabled by default.
-be controlled with the **`strict_multi_stmt`** router option. This option is
-enabled by default.
 
-If set to false, queries are routed normally after a multi-statement query.
+When a client executes a multi-statement query, it will be treated as if it were
+a DML statement and routed to the master. If the option is enabled, all queries
+after a multi-statement query will be routed to the master to guarantee a
+consistent session state.
 
-**Warning:** this can cause false data to be read from the slaves if the
+If the feature is disabled, queries are routed normally after a multi-statement
-multi-statement query modifies the session state. Only disable the strict mode
+query.
-if you know that no changes to the session state will be made inside the
+
-multi-statement queries.
+**Warning:** Enable the strict mode only if you know that the clients will send
+  statements that cause inconsistencies in the session state.
 
 ```
-# Disable strict multi-statement mode
+# Enable strict multi-statement mode
-router_options=strict_multi_stmt=false
+router_options=strict_multi_stmt=true
 ```
 
 ### `strict_sp_calls`

server/modules/routing/readwritesplit/readwritesplit.cc

@@ -1432,7 +1432,7 @@ MXS_MODULE *MXS_CREATE_MODULE()
             {"retry_failed_reads", MXS_MODULE_PARAM_BOOL, "true"},
             {"disable_sescmd_history", MXS_MODULE_PARAM_BOOL, "true"},
             {"max_sescmd_history", MXS_MODULE_PARAM_COUNT, "0"},
-            {"strict_multi_stmt",  MXS_MODULE_PARAM_BOOL, "true"},
+            {"strict_multi_stmt",  MXS_MODULE_PARAM_BOOL, "false"},
             {"strict_sp_calls",  MXS_MODULE_PARAM_BOOL, "false"},
             {"master_accept_reads", MXS_MODULE_PARAM_BOOL, "false"},
             {"connection_keepalive", MXS_MODULE_PARAM_COUNT, "0"},