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MySQL 5.7 Reference Manual  /  ...  /  Performance Schema Connection Attribute Tables

25.12.9 Performance Schema Connection Attribute Tables

Connection attributes are key-value pairs that application programs can pass to the server at connect time. For applications based on the C API implemented by the libmysqlclient client library, the mysql_options() and mysql_options4() functions define the connection attribute set. Other MySQL Connectors may provide their own attribute-definition methods.

These Performance Schema tables expose attribute information:

Attribute names that begin with an underscore (_) are reserved for internal use and should not be created by application programs. This convention permits new attributes to be introduced by MySQL without colliding with application attributes, and enables application programs to define their own attributes that do not collide with internal attributes.

Available Connection Atrributes

The set of connection attributes visible within a given connection varies depending on factors such as your platform, MySQL Connector used to establish the connection, or client program.

The libmysqlclient client library sets these attributes:

  • _client_name: The client name (libmysql for the client library).

  • _client_version: The client library version.

  • _os: The operating system (for example, Linux, Win64).

  • _pid: The client process ID.

  • _platform: The machine platform (for example, x86_64).

  • _thread: The client thread ID (Windows only).

Other MySQL Connectors may define their own connection attributes.

MySQL Connector/J defines these attributes:

  • _client_license: The connector license type.

  • _runtime_vendor: The Java runtime environment (JRE) vendor.

  • _runtime_version: The Java runtime environment (JRE) version.

MySQL Connector/NET defines these attributes:

  • _client_version: The client library version.

  • _os: The operating system (for example, Linux, Win64).

  • _pid: The client process ID.

  • _platform: The machine platform (for example, x86_64).

  • _program_name: The client name.

  • _thread: The client thread ID (Windows only).

PHP defines attributes that depend on how it was compiled:

  • Compiled using libmysqlclient: The standard libmysqlclient attributes, described previously.

  • Compiled using mysqlnd: Only the _client_name attribute, with a value of mysqlnd.

Many MySQL client programs set a program_name attribute with a value equal to the client name. For example, mysqladmin and mysqldump set program_name to mysqladmin and mysqldump, respectively.

Some MySQL client programs define additional attributes:

  • mysqlbinlog:

    • _client_role: binary_log_listener

  • Replica connections:

    • program_name: mysqld

    • _client_role: binary_log_listener

    • _client_replication_channel_name: The channel name.

  • FEDERATED storage engine connections:

    • program_name: mysqld

    • _client_role: federated_storage

Connection Atrribute Limits

There are limits on the amount of connection attribute data transmitted from client to server:

  • A fixed limit imposed by the client prior to connect time.

  • A fixed limit imposed by the server at connect time.

  • A configurable limit imposed by the Performance Schema at connect time.

For connections initiated using the C API, the libmysqlclient library imposes a limit of 64KB on the aggregate size of connection attribute data on the client side: Calls to mysql_options() that cause this limit to be exceeded produce a CR_INVALID_PARAMETER_NO error. Other MySQL Connectors may impose their own client-side limits on how much connection attribute data can be transmitted to the server.

On the server side, these size checks on connection attribute data occur:

  • The server imposes a limit of 64KB on the aggregate size of connection attribute data it can accept. If a client attempts to send more than 64KB of attribute data, the server rejects the connection.

  • For accepted connections, the Performance Schema checks aggregate attribute size against the value of the performance_schema_session_connect_attrs_size system variable. If attribute size exceeds this value, these actions take place:

    • The Performance Schema truncates the attribute data and increments the Performance_schema_session_connect_attrs_lost status variable, which indicates the number of connections for which attribute truncation occurred.

    • The Performance Schema writes a message to the error log if the log_error_verbosity system variable is greater than 1:

      [Warning] Connection attributes of length N were truncated