Vertica provides several methods for database administrators to view and control sessions. The methods vary according to the type of session:
- External (user) sessions are initiated by vsql or programmatic (ODBC or JDBC) connections and have associated client state.
- Internal (system) sessions are initiated by Vertica and have no client state.
Configuring Maximum Sessions
The maximum number of per-node user sessions is set by the configuration parameter
MaxClientSessions parameter, by default 50. You can set
MaxClientSessions parameter to any value between 0 and 1000. In addition to this maximum, Vertica also allows up to five administrative sessions per node.
=> ALTER DATABASE DEFAULT SET MaxClientSessions = 100;
If you use the Administration Tools "Connect to Database" option, Vertica will attempt connections to other nodes if a local connection does not succeed. These cases can result in more successful "Connect to Database" commands than you would expect given the
The system table
SESSIONS contains detailed information about user sessions and returns one row per session. Superusers have unrestricted access to all database metadata. Access for other users varies according to their privileges.
You can interrupt a running statement with the Vertica function
INTERRUPT_STATEMENT. Interrupting a running statement returns a session to an idle state:
- No statements or transactions are running.
- No locks are held.
- The database is doing no work on behalf of the session.
Closing a user session interrupts the session and disposes of all state related to the session, including client socket connections for the target sessions. The following Vertica functions close one or more user sessions:
SELECT statements that call these functions return after the interrupt or close message is delivered to all nodes. The function might return before Vertica completes execution of the interrupt or close operation. Thus, there might be a delay after the statement returns and the interrupt or close takes effect throughout the cluster. To determine if the session or transaction ended, query the
SESSIONS system table.
In order to shut down a database, you must first close all user sessions. For more about database shutdown, see Stopping the Database.