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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 * 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 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 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 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 * 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 ### 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 : 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 :