Oracle error
ORA-00018
ORA-00018: maximum number of sessions exceeded
What usually causes it
The instance reached its SESSIONS limit. A connection pool that opens sessions faster than it closes them is the usual source.
What to check first
Compare current and peak sessions to the limit, and see which users and machines hold them. Fix the leak before raising SESSIONS, which needs a restart.
Scripts that help
- Processes and sessions against their limitsCurrent and peak usage of processes, sessions and transactions since startup. A PEAK % near 100 means the next connection storm will hit ORA-00020.
- Session count by user and machineWho is connected, from where, and how many are active. The quickest way to spot a connection pool that has run away.