有个项目也遇到类似的问题，也是12C环境
Oracle Linux 7.9 RAC 12.2.0.1版本的
提示连接超时，网上只能找到10g出现类似问题解决办法，10g主要是长连接没有释放，最终没有找到解决办法。是不是连接请求太多太频繁了？

2019-12-19T11:48:17.333690+08:00

Fatal NI connect error 12170.

VERSION INFORMATION:
TNS for Linux: Version 12.2.0.1.0 - Production
Oracle Bequeath NT Protocol Adapter for Linux: Version 12.2.0.1.0 - Production
TCP/IP NT Protocol Adapter for Linux: Version 12.2.0.1.0 - Production
Time: 19-DEC-2019 11:48:17
Tracing not turned on.
Tns error struct:
ns main err code: 12535

TNS-12535: TNS:operation timed out
ns secondary err code: 12606
nt main err code: 0
nt secondary err code: 0
nt OS err code: 0
Client address: (ADDRESS=(PROTOCOL=tcp)(HOST=10.1.104.17)(PORT=54024))
2019-12-19T11:48:17.345482+08:00
WARNING: inbound connection timed out (ORA-3136)
2019-12-19T11:55:13.095233+08:00

Fatal NI connect error 12170.

VERSION INFORMATION:
TNS for Linux: Version 12.2.0.1.0 - Production
Oracle Bequeath NT Protocol Adapter for Linux: Version 12.2.0.1.0 - Production
TCP/IP NT Protocol Adapter for Linux: Version 12.2.0.1.0 - Production
Time: 19-DEC-2019 11:55:13
Tracing not turned on.
Tns error struct:
ns main err code: 12535

TNS-12535: TNS:operation timed out
ns secondary err code: 12606
nt main err code: 0
nt secondary err code: 0
nt OS err code: 0
Client address: (ADDRESS=(PROTOCOL=tcp)(HOST=10.1.104.17)(PORT=54118))
2019-12-19T11:55:13.096457+08:00
WARNING: inbound connection timed out (ORA-3136)
2019-12-19T11:58:37.831017+08:00

Fatal NI connect error 12170.

VERSION INFORMATION:
TNS for Linux: Version 12.2.0.1.0 - Production
Oracle Bequeath NT Protocol Adapter for Linux: Version 12.2.0.1.0 - Production
TCP/IP NT Protocol Adapter for Linux: Version 12.2.0.1.0 - Production
Time: 19-DEC-2019 11:58:37
Tracing not turned on.
Tns error struct:
ns main err code: 12535

TNS-12535: TNS:operation timed out
ns secondary err code: 12606
nt main err code: 0
nt secondary err code: 0
nt OS err code: 0
Client address: (ADDRESS=(PROTOCOL=tcp)(HOST=10.0.13.206)(PORT=4750))
2019-12-19T11:58:37.831955+08:00
WARNING: inbound connection timed out (ORA-3136)