Oracle Database / Connections & Oracle Net
ORA-12518: investigate listener handoff failures
A listener may identify a service but fail to hand the connection to a server process. Correlate the failure with instance resource and operating-system evidence.
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, limit_value FROM v$resource_limit WHERE resource_name IN ('processes','sessions');Read the result
Current resource use can identify a capacity constraint but cannot explain every handoff failure. Listener and server error stacks provide the necessary context.
Resolve and verify
Compare the error time with process limits, memory pressure and server startup failures. Correct the demonstrated constraint and validate a small controlled login burst.
Operational precautions
Do not raise connection limits without checking OS limits and memory capacity. A successful later query does not rule out earlier exhaustion.