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Updated documentation about multi-statements

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The readwritesplit documentation now explains the multi-statement behavior in
more detail and provides information about situations where the default
multi-statement behavior can be disabled.
This commit is contained in:
Markus Makela
2016-03-03 13:09:50 +02:00
parent 1af26c0af6
commit 62cf248702
2 changed files with 15 additions and 0 deletions
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2
About/Limitations.md
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@ -32,6 +32,8 @@ In master-slave replication cluster also read-only queries are routed to master
* statement includes a stored procedure, or an UDF call
### Multi-statement limitations
If the client enables and executes multi-statements, they will be routed to
the master. All future queries will also be routed to the master to guarantee
a consistent session state after the multi-statement query. This behavior can

13
Routers/ReadWriteSplit.md
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@ -173,6 +173,19 @@ In Master-Slave replication cluster also read-only queries are routed to master
* statement includes a stored procedure, or an UDF call
* if there are multiple statements inside one query e.g. `INSERT INTO ... ; SELECT LAST_INSERT_ID();`
### Limitations in multi-statement handling
When a multi-statemet query is executed through the readwritesplit router, it will always
be routed to the master. With the default configuration, all queries after a
multi-statement query will be routed to the master to prevent possible reads of
false data. You can override this behavior with the `strict_multi_stmt=false`
router option. In this mode, the multi-statement queries will still be routed
to the master but individual statements are routed normally. If you use
multi-statements and you know they don't modify the session state in any
relevant way, you can disable this option for better performance.
### Limitations in client session handling
Some of the queries that client sends are routed to all backends instead of sending them just to one of server. These queries include `USE <db name>` and `SET autocommit=0` among many others. Readwritesplit sends a copy of these queries to each backend server and forwards the master's reply to the client. Below is a list of MySQL commands which are classified as session commands :