Oracle Database / Sessions, Locks & Transactions
ORA-00018: investigate the maximum session limit
A session ceiling can reject new work even while existing sessions appear idle. Measure usage and explain which client groups own it.
Environment and inputs: Oracle Database 19c baseline · SQL*Plus-compatible SQL unless RMAN, DGMGRL, ADRCI or a host shell is specified. Check release, patch level, edition and container first.
Start with this diagnostic
Use the stated SQL, RMAN, DGMGRL or host shell and replace sample names with approved targets. DBA and V$ views need authorized catalog access in the correct container. Do not grant broad privileges for an example.
SELECT resource_name, current_utilization, max_utilization, limit_value FROM v$resource_limit WHERE resource_name = 'sessions';Read the result
The view shows current use, an instance-lifetime high-water mark and the configured limit. Peaks and connection distribution matter more than one normal snapshot.
Resolve and verify
Group application sessions and compare pool limits with replica counts. Fix leaks or excessive pools before planning a capacity increase.
Operational precautions
Session changes can interact with process capacity, memory and restart requirements. Do not increase limits without resource planning.