Exasol can handle about 10,000 sessions per node. These sessions can be either active or inactive. A session is defined as active if it matches at least one of the following conditions:
- Performs query execution
- Has an open transaction
- Has an open prepared statement
- Has an open result set
- Has an open sub-connection
Each active session occupies one active slot. The number of the active slots globally (not per node) is limited to 100 by default. When transitioning from an inactive to an active session, the session may wait for an active slot to become available. In such a case, the status QUEUED will be displayed for all the waiting sessions in the STATUS column of EXA_ALL_SESSIONS table. All sessions waiting for an active slot are served in a FIFO manner.
Reaching the active session limit is not necessarily a cause for concern. Additional sessions are queued until an active slot is available and are then executed.