Mysqlnd_ms Functions
PHP Manual

mysqlnd_ms_query_is_select

Find whether to send the query to the master, the slave or the last used MySQL server

Description

int mysqlnd_ms_query_is_select ( string $query )

Finds whether to send the query to the master, the slave or the last used MySQL server.

The plugins built-in read/write split mechanism will be used to analyze the query string to make a recommendation where to send the query. The built-in read/write split mechanism is very basic and simple. The plugin will recommend sending all queries to the MySQL replication master server but those which begin with SELECT, or begin with a SQL hint which enforces sending the query to a slave server. Due to the basic but fast algorithm the plugin may propose to run some read-only statements such as SHOW TABLES on the replication master.

Parameters

query

Query string to test.

Return Values

A return value of MYSQLND_MS_QUERY_USE_MASTER indicates that the query should be send to the MySQL replication master server. The function returns a value of MYSQLND_MS_QUERY_USE_SLAVE if the query can be run on a slave because it is considered read-only. A value of MYSQLND_MS_QUERY_USE_LAST_USED is returned to recommend running the query on the last used server. This can either be a MySQL replication master server or a MySQL replication slave server.

If read write splitting has been disabled by setting mysqlnd_ms.disable_rw_split, the function will always return MYSQLND_MS_QUERY_USE_MASTER or MYSQLND_MS_QUERY_USE_LAST_USED.

Examples

Example #1 mysqlnd_ms_query_is_select example

<?php
function is_select($query)
{
 switch (mysqlnd_ms_query_is_select($query))
 {
  case MYSQLND_MS_QUERY_USE_MASTER:
   printf("'%s' should be run on the master.\n", $query);
   break;
  case MYSQLND_MS_QUERY_USE_SLAVE:
   printf("'%s' should be run on a slave.\n", $query);
   break;
  case MYSQLND_MS_QUERY_USE_LAST_USED:
   printf("'%s' should be run on the server that has run the previous query\n", $query);
   break;
  default:
   printf("No suggestion where to run the '%s', fallback to master recommended\n", $query);
   break;
 }
}

is_select("INSERT INTO test(id) VALUES (1)");
is_select("SELECT 1 FROM DUAL");
is_select("/*" . MYSQLND_MS_LAST_USED_SWITCH . "*/SELECT 2 FROM DUAL");
?>

The above example will output:

INSERT INTO test(id) VALUES (1) should be run on the master.
SELECT 1 FROM DUAL should be run on a slave.
/*ms=last_used*/SELECT 2 FROM DUAL should be run on the server that has run the previous query