The DataStream feature supports only the UTF-8 charset.

The character set used by the client while sending a request might be different from the character set used in the database server responses. Although the charset parameter is set during the connection establishment, it can be changed at any time by sending an SQL query. The character set is associated with a connection, and therefore, requests on connections with one character set can’t be multiplexed onto a connection with a different character set.

The NetScaler appliance parses the queries sent by the client and the responses sent by the database server.

The character set associated with a connection can be changed after the initial handshake by using the following two queries:

In MySQL, transactions are identified by using the connection parameter AUTOCOMMIT or the BEGIN:COMMIT queries. The AUTOCOMMIT parameter can be set during the initial handshake, or after the connection is established by using the query SET AUTOCOMMIT.

The NetScaler appliance explicitly parses each query to determine the beginning and end of a transaction.

In the MySQL protocol, the response contains two flags to indicate whether the connection is a transaction: the TRANSACTION and AUTOCOMMIT flags.

If the connection is a transaction, the TRANSACTION flag is set. Or, if the AutoCommit mode is OFF, the AUTOCOMMIT flag isn’t set. The ADC appliance parses the response, and if either the TRANSACTION flag is set or the AUTOCOMMIT flag isn’t set, it does not do connection multiplexing. When these conditions are no longer true, the ADC appliance begins connection multiplexing.

There are special queries, such as SET and PREPARE, that modify the state of the connection and might break request switching, and therefore, these queries need to be handled differently.

On receiving a request with special queries, the NetScaler appliance sends an OK response to the client and also, stores the request in the connection.

When a non-special query, such as INSERT and SELECT, is received along with a stored query, the ADC appliance looks for the server-side connection on which the stored query has already been sent to the database server. If no such connections exist, the ADC appliance creates a connection, and sends the stored query first, and then, sends the request with the non-special query.

In SET, USE db, and INIT_DB special queries, the appliance modifies a field in the server side connection corresponding to the special query. This modification results in better reuse of the server side connection.

Only 16 queries are stored in each connection.

The following is a list of the special queries for which the ADC appliance has a modified behavior.

You can now configure the NetScaler appliance to generate audit log messages for the DataStream feature. Audit log messages are generated when client-side and server-side connections are established, closed, or dropped. The categories of messages that you can log and view are ERROR and INFO. Error messages for client-side connections begin with "CS" and error messages for server-side connections begin with "SS." Additional information is provided where necessary. For example, log messages for closed connections (CS_CONN_CLOSED) include only the connection ID. However, log messages for established connections (CS_CONN_ESTD) include information such as the user name, database name, and the client IP address in addition to the connection ID.