diff --git a/Documentation/Reference/Hint-Syntax.md b/Documentation/Reference/Hint-Syntax.md index 69ea8446f..e8b942807 100644 --- a/Documentation/Reference/Hint-Syntax.md +++ b/Documentation/Reference/Hint-Syntax.md @@ -2,7 +2,8 @@ ## Enabling routing hints -To enable routing hints for a service, the hintfilter module needs to be configured and the filter needs to be applied to the service. +To enable routing hints for a service, the hintfilter module needs to be +configured and the filter needs to be applied to the service. Here is an example service which has the hint filter configured and applied. @@ -24,12 +25,16 @@ module=hintfilter ## Comments and comment types -The client connection will need to have comments enabled. For example the `mysql` command line client has comments disabled by default and they need to be enabled by passing the `-c` option. +The client connection will need to have comments enabled. For example the +`mysql` command line client has comments disabled by default and they need +to be enabled by passing the `-c` option. -For comment types, use either `-- ` (notice the whitespace after the double hyphen) or `#` after the semicolon or `/* .. */` before the semicolon. +For comment types, use either `-- ` (notice the whitespace after the double +hyphen) or `#` after the semicolon or `/* .. */` before the semicolon. -The MySQL manual doesn't specify if comment blocks, i.e. `/* .. */`, should contain a -whitespace character before or after the tags, so adding whitespace at both the start and the end is advised. +The MySQL manual doesn't specify if comment blocks, i.e. `/* .. */`, should +contain a whitespace character before or after the tags, so adding +whitespace at both the start and the end is advised. ## Hint body @@ -49,7 +54,12 @@ These hints will instruct the router to route a query to a certain type of a ser -- maxscale route to [master | slave | server ] ``` -A `master` value in a routing hint will route the query to a master server. This can be used to direct read queries to a master server for a up-to-date result with no replication lag. A `slave` value will route the query to a slave server. A `server` value will route the query to a named server. The value of needs to be the same as the server section name in maxscale.cnf. +A `master` value in a routing hint will route the query to a master +server. This can be used to direct read queries to a master server for a +up-to-date result with no replication lag. A `slave` value will route the +query to a slave server. A `server` value will route the query to a named +server. The value of needs to be the same as the server +section name in maxscale.cnf. ### Name-value hints @@ -59,12 +69,15 @@ These control the behavior and affect the routing decisions made by the router. -- maxscale = ``` -Currently the only accepted parameter is `max_slave_replication_lag`. This will route the query to a server with lower replication lag then what is defined in the hint value. +Currently the only accepted parameter is `max_slave_replication_lag`. This +will route the query to a server with lower replication lag then what is +defined in the hint value. ## Hint stack -Hints can be either single-use hints, which makes them affect only one query, or named -hints, which can be pushed on and off a stack of active hints. +Hints can be either single-use hints, which makes them affect only one +query, or named hints, which can be pushed on and off a stack of active +hints. Defining named hints: @@ -90,7 +103,8 @@ You can define and activate a hint in a single command using the following: -- maxscale begin ``` -You can also push anonymous hints onto the stack which are only used as long as they are on the stack: +You can also push anonymous hints onto the stack which are only used as long +as they are on the stack: ``` -- maxscale begin @@ -100,7 +114,8 @@ You can also push anonymous hints onto the stack which are only used as long as ### Example 1 - Routing SELECT queries to master -In this example, MariaDB MaxScale is configured with the readwritesplit router and the hint filter. +In this example, MariaDB MaxScale is configured with the readwritesplit +router and the hint filter. ``` [ReadWriteService] @@ -116,11 +131,17 @@ type=filter module=hintfilter ``` -Behind MariaDB MaxScale is a master server and a slave server. If there is replication lag between the master and the slave, read queries sent to the slave might return old data. To guarantee up-to-date data, we can add a routing hint to the query. +Behind MariaDB MaxScale is a master server and a slave server. If there is +replication lag between the master and the slave, read queries sent to the +slave might return old data. To guarantee up-to-date data, we can add a +routing hint to the query. ``` INSERT INTO table1 VALUES ("John","Doe",1); SELECT * from table1; -- maxscale route to master ``` -The first INSERT query will be routed to the master. The following SELECT query would normally be routed to the slave but with the added routing hint it will be routed to the master. This way we can do an INSERT and a SELECT right after it and still get up-to-date data. +The first INSERT query will be routed to the master. The following SELECT +query would normally be routed to the slave but with the added routing hint +it will be routed to the master. This way we can do an INSERT and a SELECT +right after it and still get up-to-date data.