[SOL-296] Session management in EXASolution Created: 28.07.2015  Updated: 14.11.2019  Resolved: 14.11.2019

Status: Obsolete
Project: Solution Center
Component/s: EXASolution
Affects Version/s: EXASolution 5.0, EXASOL 6.0.0, Exasol 6.1.0
Fix Version/s: None

Type: Explanation
Reporter: Captain EXASOL Assignee: Captain EXASOL
Labels: None

Issue Links:
Related
relates EXASOL-1531 Improved session and resource managem... Resolved
relates EXASOL-1598 Decrease notification level in cases ... Resolved
is related to SOL-39 Connection management in EXASolution ... Obsolete
Explanation:

Note: This solution is no longer maintained. For the latest information, please refer to our documentation:

https://docs.exasol.com/database_concepts/session_management.htm

 

EXASolution is able to handle 10.000 sessions per node. These sessions can be either active or inactive.
Session is defined as active if matches at least one of the following conditions:

  • doing login authorization
  • doing query execution
  • has open transaction
  • has open prepared statement
  • has open resultset
  • has open subconnection

Each active session occupies one active slot. The number of the active slots is limited per default to 100 (globally, not per node). In inactive to active transition the session may wait for active slot to becomes available. In such case the status QUEUED will be shown for all waiting sessions in the STATUS column of EXA_*SESSIONS. All waiting for _active slot sessions are served in FIFO manner.

Since EXASolution 5.0.11 there are 100 additional active but blocked session slots available for sessions that are waiting for another session. Typically they are waiting for commit and have status "Waiting for session" in the ACTIVITY column of EXA_*_SESSIONS. If the number of the blocked sessions exceeds the
active but blocked session slots count then the remaining free active slots are used for them (see EXASOL-1531).

Since EXASolution 5.0.12 an EXAoperation warning is generated if 80% of the maximum allowed active session slots are in use:

Query queue limit of active sessions nearly reached, 
running: <<active_sessions>> of 100 (+ <<blocked_sessions>> WAIT FOR COMMIT) are in use. 
Total number of sessions: <<all_sessions>>.

If a login request can't be processed and has to wait because no free active session slots are available, an EXAoperation warning will be periodically logged until all requests have been processed:

Limit of active sessions has been reached.


Note: Before EXASolution 5.0 a session is counted always as active after setting AUTOCOMMIT OFF. In order to free the used active session slot, an explicit COMMIT needs to be done right after the AUTOCOMMIT OFF command.

Category 1: Database Administration
Category 2: Clients, Interfaces & Drivers
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