The behaviour of these functions is affected by settings in php.ini.
Here's a short explanation of the configuration directives.
If enabled, the plugin checks if the host (server) parameters value of any MySQL connection attempt, matches a section name from the plugin configuration file. If not, the connection attempt is blocked.
This setting is not only useful to restrict PHP to certain servers but also to debug configuration file problems. The configuration file validity is checked at two different stages. The first check is performed when PHP begins to handle a web request. At this point the plugin reads and decodes the configuration file. Errors thrown at this early stage in an extensions life cycle may not be shown properly to the user. Thus, the plugin buffers the errors, if any, and additionally displays them when establishing a connection to MySQL. By default a buffered startup error will emit an error of type E_WARNING. If force_config_usage is set, the error type used is E_RECOVERABLE_ERROR.
Please, see also configuration file debugging notes.
Plugin specific configuration file. This setting has been renamed to mysqlnd_ms.config_file in version 1.4.0.
Plugin specific configuration file. This setting superseeds mysqlnd_ms.ini_file since 1.4.0.
Enables or disables the collection of statistics. The collection of statistics is disabled by default for performance reasons. Statistics are returned by the function mysqlnd_ms_get_stats().
Enables or disables support of MySQL multi master replication setups. Please, see also supported clusters.
Enables or disables built-in read write splitting.
Controls whether load balancing and lazy connection functionality can be used independently of read write splitting. If read write splitting is disabled, only servers from the master list will be used for statement execution. All configured slave servers will be ignored.
The SQL hint MYSQLND_MS_USE_SLAVE will not be recognized. If found, the statement will be redirected to a master.
Disabling read write splitting impacts the return value of mysqlnd_ms_query_is_select(). The function will no longer propose query execution on slave servers.
Note: Multiple master servers
Setting mysqlnd_ms.multi_master=1 allows the plugin to use multiple master servers, instead of only the first master server of the master list.
Please, see also supported clusters.