php man page for mysqlnd_ms_set_user_pick_server

MYSQLND_MS_SET_USER_PICK_SERVER(3)					 1					MYSQLND_MS_SET_USER_PICK_SERVER(3)

mysqlnd_ms_set_user_pick_server - Sets a callback for user-defined read/write splitting

SYNOPSIS
       bool mysqlnd_ms_set_user_pick_server (string  $function)

DESCRIPTION
	Sets  a  callback  for	user-defined  read/write  splitting. The plugin will call the callback only if pick[]=user is the default rule for
       server picking in the relevant section of the plugins configuration file.

	The plugins built-in read/write query split mechanism decisions can be overwritten in two ways. The easiest way is to  prepend	the  query
       string  with  the  SQL hints MYSQLND_MS_MASTER_SWITCH, MYSQLND_MS_SLAVE_SWITCH or MYSQLND_MS_LAST_USED_SWITCH. Using SQL hints one can con-
       trol, for example, whether a query shall be send to the MySQL replication master server or one of the slave servers. By help of	SQL  hints
       it is not possible to pick a certain slave server for query execution.

	Full  control  on  server selection can be gained using a callback function. Use of a callback is recommended to expert users only because
       the callback has to cover all cases otherwise handled by the plugin.

	The plugin will invoke the callback function for selecting a server from the lists of configured master and slave  servers.  The  callback
       function  inspects  the	query  to  run and picks a server for query execution by returning the hosts URI, as found in the master and slave
       list.

	If the lazy connections are enabled and the callback chooses a slave server for which no connection has been established so far and estab-
       lishing the connection to the slave fails, the plugin will return an error upon the next action on the failed connection, for example, when
       running a query. It is the responsibility of the application developer to handle the error. For example, the  application  can  re-run  the
       query  to  trigger a new server selection and callback invocation. If so, the callback must make sure to select a different slave, or check
       slave availability, before returning to the plugin to prevent an endless loop.

PARAMETERS
	      o $function
		- The function to be called. Class methods may also be	invoked  statically  using  this  function  by	passing  array($classname,
		$methodname)  to  this parameter. Additionally class methods of an object instance may be called by passing array($objectinstance,
		$methodname) to this parameter.

RETURN VALUES
	Host to run the query on. The host URI is to be taken from the master and slave connection lists passed to the callback function. If call-
       back  returns a value neither found in the master nor in the slave connection lists the plugin will fallback to the second pick method con-
       figured via the pick[] setting in the plugin configuration file. If not second pick method is given, the plugin falls back to the  build-in
       default pick method for server selection.

NOTES
       Note

	      mysqlnd_ms_set_user_pick_server(3) is available with PECL mysqlnd_ms < 1.1.0. It has been replaced by the user filter. Please, check
	      the Change History for upgrade notes.

EXAMPLES
       Example #1

	      mysqlnd_ms_set_user_pick_server(3) example

	      [myapp]
	      master[] = localhost
	      slave[] = 192.168.2.27:3306
	      slave[] = 192.168.78.136:3306
	      pick[] = user

	      <?php

	      function pick_server($connected, $query, $master, $slaves, $last_used)
	      {
	       static $slave_idx = 0;
	       static $num_slaves = NULL;
	       if (is_null($num_slaves))
		$num_slaves = count($slaves);

	       /* default: fallback to the plugins build-in logic */
	       $ret = NULL;

	       printf("User has connected to '%s'...
", $connected);
	       printf("... deciding where to run '%s'
", $query);

	       $where = mysqlnd_ms_query_is_select($query);
	       switch ($where)
	       {
		case MYSQLND_MS_QUERY_USE_MASTER:
		 printf("... using master
");
		 $ret = $master[0];
		 break;
		case MYSQLND_MS_QUERY_USE_SLAVE:
		 /* SELECT or SQL hint for using slave */
		 if (stristr($query, "FROM table_on_slave_a_only"))
		 {
		  /* a table which is only on the first configured slave  */
		  printf("... access to table available only on slave A detected
");
		  $ret = $slaves[0];
		 }
		 else
		 {
		  /* round robin */
		  printf("... some read-only query for a slave
");
		  $ret = $slaves[$slave_idx++ % $num_slaves];
		 }
		 break;
		case MYSQLND_MS_QUERY_LAST_USED:
		 printf("... using last used server
");
		 $ret = $last_used;
		 break;
	       }

	       printf("... ret = '%s'
", $ret);
	       return $ret;
	      }

	      mysqlnd_ms_set_user_pick_server("pick_server");

	      $mysqli = new mysqli("myapp", "root", "root", "test");

	      if (!($res = $mysqli->query("SELECT 1 FROM DUAL")))
	       printf("[%d] %s
", $mysqli->errno, $mysqli->error);
	      else
	       $res->close();

	      if (!($res = $mysqli->query("SELECT 2 FROM DUAL")))
	       printf("[%d] %s
", $mysqli->errno, $mysqli->error);
	      else
	       $res->close();

	      if (!($res = $mysqli->query("SELECT * FROM table_on_slave_a_only")))
	       printf("[%d] %s
", $mysqli->errno, $mysqli->error);
	      else
	       $res->close();

	      $mysqli->close();
	      ?>

	      The above example will output:

	      User has connected to 'myapp'...
	      User has connected to 'myapp'...
	      User has connected to 'myapp'...

SEE ALSO
       mysqlnd_ms_query_is_select(3), Filter concept, user filter .

PHP Documentation Group 											MYSQLND_MS_SET_USER_PICK_SERVER(3)