[oracle@D2-PISIT22 ~]$ sqlplus lissit/lissit@10.163.91.22:1521/pocsit02
SQL*Plus: Release 11.2.0.4.0 Production on Thu May 11 08:51:49 2017
Copyright (c) 1982, 2013, Oracle. All rights reserved.
ERROR:
ORA-12516: TNS:listener could not find available handler with matching protocol
stack
查看监听服务：
[oracle@D2-PISIT22 ~]$ lsnrctl services
LSNRCTL for Linux: Version 11.2.0.4.0 - Production on 11-MAY-2017 08:50:53
Copyright (c) 1991, 2013, Oracle. All rights reserved.
Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521))
Services Summary...
Service "pocsit02" has 1 instance(s).
Instance "pocsit02", status READY, has 1 handler(s) for this service...
Handler(s):
"DEDICATED" established:8095 refused:0 state:blocked
LOCAL SERVER
Service "pocsit02XDB" has 1 instance(s).
Instance "pocsit02", status READY, has 1 handler(s) for this service...
Handler(s):
"D000" established:0 refused:0 current:0 max:1022 state:ready
DISPATCHER
(ADDRESS=(PROTOCOL=tcp)(HOST=D2-PISIT22)(PORT=54841))
The command completed successfully
可以看到对于实例pocsit02的服务pocsit02，已经创建了8095个连接，状态为blocked，处于封锁状态。
这个问题对于测试环境，直接重启监听和数据库ok了，但生产环境就不能使用这么重的方式了，可以执行如下语句重新让pmon注册一下监听：
SQL> alter system register;
System altered.
[oracle@D2-PISIT22 ~]$ lsnrctl services
LSNRCTL for Linux: Version 11.2.0.4.0 - Production on 11-MAY-2017 08:54:42
Copyright (c) 1991, 2013, Oracle. All rights reserved.
Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521))
Services Summary...
Service "pocsit02" has 1 instance(s).
Instance "pocsit02", status READY, has 1 handler(s) for this service...
Handler(s):
"DEDICATED" established:8100 refused:0 state:ready
LOCAL SERVER
Service "pocsit02XDB" has 1 instance(s).
Instance "pocsit02", status READY, has 1 handler(s) for this service...
Handler(s):
"D000" established:0 refused:0 current:0 max:1022 state:ready
DISPATCHER
(ADDRESS=(PROTOCOL=tcp)(HOST=D2-PISIT22)(PORT=54841))
The command completed successfully
可以看到状态变为ready了。也可以对监听开一下跟踪，然后关掉的方式来解决这个问题并重置连接数：
SQL> alter system set events='immediate trace name listener_registration level 3';
System altered.
SQL> alter system set events='immediate trace name listener_registration level 0';
System altered.
[oracle@D2-PISIT22 ~]$ lsnrctl services
LSNRCTL for Linux: Version 11.2.0.4.0 - Production on 11-MAY-2017 08:55:58
Copyright (c) 1991, 2013, Oracle. All rights reserved.
Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521))
Services Summary...
Service "pocsit02" has 1 instance(s).
Instance "pocsit02", status READY, has 1 handler(s) for this service...
Handler(s):
"DEDICATED" established:2 refused:0 state:ready
LOCAL SERVER
Service "pocsit02XDB" has 1 instance(s).
Instance "pocsit02", status READY, has 1 handler(s) for this service...
Handler(s):
"D000" established:0 refused:0 current:0 max:1022 state:ready
DISPATCHER
(ADDRESS=(PROTOCOL=tcp)(HOST=D2-PISIT22)(PORT=54841))
The command completed successfully