SESSION_CONNECT_ATTRS

The SESSION_CONNECT_ATTRS table provides information about connection attributes. Session attributes are key-value pairs that are sent by the client when establishing a connection.

Common attributes:

You can view the columns of the SESSION_CONNECT_ATTRS table as follows:

USE performance_schema;
DESCRIBE session_connect_attrs;

+------------------+-----------------+------+------+---------+-------+
| Field            | Type            | Null | Key  | Default | Extra |
+------------------+-----------------+------+------+---------+-------+
| PROCESSLIST_ID   | bigint unsigned | NO   |      | NULL    |       |
| ATTR_NAME        | varchar(32)     | NO   |      | NULL    |       |
| ATTR_VALUE       | varchar(1024)   | YES  |      | NULL    |       |
| ORDINAL_POSITION | int             | YES  |      | NULL    |       |
+------------------+-----------------+------+------+---------+-------+

You can view the information on session attributes stored in the SESSION_CONNECT_ATTRS table as follows:

USE performance_schema;
TABLE SESSION_CONNECT_ATTRS;

+----------------+-----------------+------------+------------------+
| PROCESSLIST_ID | ATTR_NAME       | ATTR_VALUE | ORDINAL_POSITION |
+----------------+-----------------+------------+------------------+
|        2097154 | _client_name    | libmysql   |                0 |
|        2097154 | _client_version | 8.5.0      |                1 |
|        2097154 | _os             | Linux      |                2 |
|        2097154 | _pid            | 1299203    |                3 |
|        2097154 | _platform       | x86_64     |                4 |
|        2097154 | program_name    | mysqlsh    |                5 |
+----------------+-----------------+------------+------------------+

Fields in the SESSION_CONNECT_ATTRS table are described as follows:

• PROCESSLIST_ID: Processlist ID of the session.
• ATTR_NAME: Attribute name.
• ATTR_VALUE: Attribute value.
• ORDINAL_POSITION: Ordinal position of the name/value pair.

Size limit and truncation

TiDB uses the performance_schema_session_connect_attrs_size global system variable to control the maximum total size of connection attributes per session.

• Default value: 4096 bytes
• Range: [-1, 65536]
• -1 means no configured limit, and TiDB treats it as up to 65536 bytes.
• 0 means that TiDB does not retain client-provided session connection attributes, which effectively disables recording session attributes.

When the total size exceeds this limit, TiDB truncates excess attributes and adds _truncated to indicate the number of truncated bytes.

The accepted connection attributes are also written to the Session_connect_attrs field in the slow log and can be queried from INFORMATION_SCHEMA.SLOW_QUERY and INFORMATION_SCHEMA.CLUSTER_SLOW_QUERY. To control the payload size written to the slow log, adjust performance_schema_session_connect_attrs_size.

TiDB also enforces a hard limit of 1 MiB on connection attribute payload in handshake packets. If this hard limit is exceeded, the connection is rejected.