下列常量由此扩展定义，且仅在此扩展编译入 PHP 或在运行时动态载入时可用。
SQL hint related
Example #1 Example demonstrating the usage of mysqlnd_ms constants
The mysqlnd replication and load balancing plugin (mysqlnd_ms) performs read/write splitting. This directs write queries to a MySQL master server, and read-only queries to the MySQL slave servers. The plugin has a built-in read/write split logic. All queries which start with SELECT are considered read-only queries, which are then sent to a MySQL slave server that is listed in the plugin configuration file. All other queries are directed to the MySQL master server that is also specified in the plugin configuration file.
User supplied SQL hints can be used to overrule automatic read/write splitting, to gain full control on the process. SQL hints are standards compliant SQL comments. The plugin will scan the beginning of a query string for an SQL comment for certain commands, which then control query redirection. Other systems involved in the query processing are unaffected by the SQL hints because other systems will ignore the SQL comments.
The plugin supports three SQL hints to direct queries to either the MySQL slave servers, the MySQL master server, or the last used MySQL server. SQL hints must be placed at the beginning of a query to be recognized by the plugin.
For better portability, it is recommended to use the string constants
MYSQLND_MS_MASTER_SWITCH,
MYSQLND_MS_SLAVE_SWITCH and
MYSQLND_MS_LAST_USED_SWITCH instead of their literal
values.
<?php
/* Use constants for maximum portability */
$master_query = "/*" . MYSQLND_MS_MASTER_SWITCH . "*/SELECT id FROM test";
/* Valid but less portable: using literal instead of constant */
$slave_query = "/*ms=slave*/SHOW TABLES";
printf("master_query = '%s'\n", $master_query);
printf("slave_query = '%s'\n", $slave_query);
?>
以上例程会输出：
master_query = /*ms=master*/SELECT id FROM test slave_query = /*ms=slave*/SHOW TABLES
MYSQLND_MS_MASTER_SWITCH
(string)
MYSQLND_MS_SLAVE_SWITCH
(string)
MYSQLND_MS_LAST_USED_SWITCH
(string)
mysqlnd_ms_query_is_select() related
MYSQLND_MS_QUERY_USE_MASTER
(integer)
MYSQLND_MS_QUERY_USE_MASTER for a given query, the
built-in read/write split mechanism recommends sending the query to
a MySQL replication master server.
MYSQLND_MS_QUERY_USE_SLAVE
(integer)
MYSQLND_MS_QUERY_USE_SLAVE for a given query, the
built-in read/write split mechanism recommends sending the query to
a MySQL replication slave server.
MYSQLND_MS_QUERY_USE_LAST_USED
(integer)
MYSQLND_MS_QUERY_USE_LAST_USED for a given query, the
built-in read/write split mechanism recommends sending the query to
the last used server.
mysqlnd_ms_set_qos(), quality of service filter and service level related
MYSQLND_MS_QOS_CONSISTENCY_EVENTUAL
(integer)
MYSQLND_MS_QOS_CONSISTENCY_SESSION
(integer)
MYSQLND_MS_QOS_CONSISTENCY_STRONG
(integer)
MYSQLND_MS_QOS_OPTION_GTID
(integer)
MYSQLND_MS_QOS_OPTION_AGE
(integer)
Other
The plugins version number can be obtained using
MYSQLND_MS_VERSION or
MYSQLND_MS_VERSION_ID.
MYSQLND_MS_VERSION
is the string representation of the numerical version number
MYSQLND_MS_VERSION_ID, which is an integer such as 10000.
Developers can calculate the version number as follows.
| Version (part) | Example |
|---|---|
| Major*10000 | 1*10000 = 10000 |
| Minor*100 | 0*100 = 0 |
| Patch | 0 = 0 |
| MYSQLND_MS_VERSION_ID | 10000 |