Improved routing hint documentation.
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# Hint Syntax
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Use either ’-- ’ (notice the whitespace) or ’#’ after the semicolon or ’/* .. */’ before
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the semicolon.
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## Enabling routing hints
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The MySQL manual doesn’t specify if comment blocks, i.e. ’/* .. */’, should contain a w
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hitespace character before or after the tags.
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To enable routing hints for a service, the hintfilter module needs to be configured and the filter needs to be applied to the service.
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All hints must start with the ’maxscale tag’:
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-- maxscale <hint>
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The hints right now have two types, ones that route to a server and others that contain
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Here is an example service which has the hint filter configured and applied.
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```
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[Read Service]
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type=service
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router=readconnroute
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router_options=master
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servers=server1
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user=maxuser
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passwd=maxpwd
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filter=Hint
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[Hint]
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type=filter
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module=hintfilter
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```
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## Comments and comment types
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The client connection will need to have comments enabled. For example the `mysql` command line client has comments disabled by default.
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For comment types, use either `-- ` (notice the whitespace) or `#` after the semicolon or `/* .. */` before the semicolon. All comment types work with routing hints.
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The MySQL manual doesn`t specify if comment blocks, i.e. `/* .. */`, should contain a w
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hitespace character before or after the tags, so adding whitespace at both the start and the end is advised.
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## Hint body
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All hints must start with the `maxscale` tag.
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```
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-- maxscale <hint body>
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```
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The hints have two types, ones that route to a server and others that contain
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name-value pairs.
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Routing queries to a server:
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###Routing destination hints
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These hints will instruct the router to route a query to a certain type of a server.
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```
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-- maxscale route to [master | slave | server <server name>]
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```
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The name of the server is the same as in maxscale.cnf
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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 <server name> needs to be the same as the server section name in maxscale.cnf.
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Creating a name-value pair:
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### Name-value hints
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These control the behavior and affect the routing decisions made by the router.
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```
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-- maxscale <param>=<value>
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```
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Currently the only accepted parameter is
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’max_slave_replication_lag’
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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.
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## Hint stack
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Hints can be either single-use hints, which makes them affect only one query, or named
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hints, which can be pushed on and off a stack of active hints.
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Defining named hints:
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```
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-- maxscale <hint name> prepare <hint content>
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```
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Pushing a hint onto the stack:
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```
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-- maxscale <hint name> begin
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```
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Popping the topmost hint off the stack:
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```
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-- maxscale end
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```
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You can define and activate a hint in a single command using the following:
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```
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-- maxscale <hint name> begin <hint content>
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```
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You can also push anonymous hints onto the stack which are only used as long as they are on the stack:
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-- maxscale begin <hint content>
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```
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-- maxscale begin <hint content>
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```
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