The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.
SQL hint related
Example 21.299. 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
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); ?>
The above examples will output:
master_query = /*ms=master*/SELECT id FROM test slave_query = /*ms=slave*/SHOW TABLES
MYSQLND_MS_QUERY_USE_MASTERfor a given query, the built-in read/write split mechanism recommends sending the query to a MySQL replication master server.
MYSQLND_MS_QUERY_USE_SLAVEfor 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_USEDfor a given query, the built-in read/write split mechanism recommends sending the query to the last used server.
quality of service filter and service level related
mysqlnd_ms_set_qos. Eventual consistency is the default quality of service when reading from an asynchronous MySQL replication slave. Data returned in this service level may or may not be stale, depending on whether the selected slaves happen to have replicated the latest changes from the MySQL replication master or not.
mysqlnd_ms_set_qos. Session consistency is defined as read your writes. The client is guaranteed to see his latest changes.
mysqlnd_ms_set_qos. Strong consistency is used to ensure all clients see each others changes.
mysqlnd_ms_set_qosto parameterize session consistency.
mysqlnd_ms_set_qosto parameterize eventual consistency.
The plugins version number can be obtained using
is the string representation of the numerical version number
, which is an integer such as 10000. Developers can calculate the
version number as follows.
|Major*10000||1*10000 = 10000|
|Minor*100||0*100 = 0|
|Patch||0 = 0|