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Update limitations document

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Add note about prepared statements, transaction state and
autocommit mode.
This commit is contained in:
Johan Wikman
2017-04-21 12:31:21 +03:00
parent d7e37b94ce
commit d1959549fe
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Documentation/About/Limitations.md
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@ -21,6 +21,28 @@ collect columns, functions and tables used in the `SELECT` defining the
Consequently, the database firewall will **not** block `WITH` statements Consequently, the database firewall will **not** block `WITH` statements
where the `SELECT` of the `WITH` clause refers to forbidden columns. where the `SELECT` of the `WITH` clause refers to forbidden columns.
## Prepared Statements
For its proper functioning, MaxScale needs in general to be aware of the
transaction state and _autocommit_ mode. In order to be that, MaxScale
parses statements going through it.
However, if a transaction is commited or rolled back, or the autocommit
mode is changed using a prepared statement, MaxScale will miss that and its
internal state will be incorrect, until the transaction state or autocommit
mode is changed using an explicit statement.
For instance, after the following sequence of commands, MaxScale will still
think _autocommit_ is on:
```
set autocommit=1
PREPARE hide_autocommit FROM "set autocommit=0"
EXECUTE hide_autocommit
```
To ensure that MaxScale functions properly, do not commit or rollback a
transaction or change the autocommit mode using a prepared statement.
## Protocol limitations ## Protocol limitations
### Limitations with MySQL Protocol support (MySQLClient) ### Limitations with MySQL Protocol support (MySQLClient)