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ORA-00018: Maximum number of sessions exceeded

What it means

The instance reached the SESSIONS parameter limit.

How to fix it

Find idle or leaked sessions in v$session (connection pools that never release), fix the leak, or raise SESSIONS (needs a restart).

Catch it before it runs

ORA Error Helper
Explains ORA-/PLS- codes inside JetBrains IDEs and DataGrip.
PL/SQL Lint
Flags risky PL/SQL patterns while you type.
Oracle Plan Reader
Reads execution plans and points at the slow step.
PL/SQL in Practice
Kindle book with practical PL/SQL for working developers.

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Updated 2026-11-12.