The listener gets slower.

Environment:

AIX: 7.2 (7200-04-01_1939)

RDBMS: Database Release Update 19.7.0.0.200414

Symptoms:

The connection to the database is delayed. 

On the server itself tnsping (loop-back test) takes 10000-15000 msec.

After listener restarting, the problem disappears for a while (2-3 day), loop-back test takes 0-10 msec as normal. Sessions count remains approximately the same as before listener restarted. At the OS level (netstat) TIME_WAIT, ESTABLISHED count remains the same too.

Question:

What could be the reason?