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 with a write operation
- Has an open result set
- Has an open sub-connection
Each active session occupies one active slot. By default, the number of the active slots per cluster is limited to 100. 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.