ORA-12516, TNS: listener could not find available handler with matching protocol stack

My Application Team getting below error and unable to initiate connection to the oracle database:

error:  ORA-12516, TNS: listener could not find available handler with matching protocol stack

When I connected and checked on the database, (here my db is RAC server and using spfile)

On NODE 2:

Checking alert log file 

vi alert_DEVD2.log      

No errors found

$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Tue Nov 18 19:35:36 2014

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to:

Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

With the Partitioning, Real Application Clusters, Automatic Storage Management, Oracle Label Security,

OLAP, Data Mining, Oracle Database Vault and Real Application Testing options

SQL>

col name format a30

col value format a10

SQL> select name, value from v$spparameter where name in ('processes','sessions');

NAME                           VALUE

------------------------------ ----------

processes                      400

sessions                        400

or, check the max and current utilization of these parameters

select resource_name, current_utilization/limit_value*100,current_utilization, max_utilization,limit_value from v$resource_limit where resource_name in ('processes','sessions');

SQL>  select count(*) from v$process;

  COUNT(*)

----------

       166

On NODE 1 :

SQL> select * from v$resource_limit where resource_name in ('processes','sessions');

 vi alert_DEVD1.log      

ORA-00020: maximum number of processes (400) exceeded

 ORA-20 errors will not be written to the alert log for

 the next minute. Please look at trace files to see all

 the ORA-20 errors.

SQL> select count(*) from v$process;                

  COUNT(*)

----------

       380

SQL> select count(*) from gv$process;

  COUNT(*)

----------

       546

From the above output I see my processes are exceeded the value set by oracle(400) and resulting the error in alert log. Then checked the connections to the database:

Set linesize 280;

select count(*),INST_ID,username,osuser,status,machine from gv$session group by INST_ID,username,osuser,status,machine order by count(*),INST_ID;

(or) for single node:

select count(*),username,osuser,status,machine from v$session group by username,osuser,status,machine order by count(*);

Check the output from the above query and kill if find any INACTIVE sessions (idle)

Solution:

According to oracle, PROCESSES parameter specifies the maximum number of operating system user processes that can simultaneously connect to Oracle.

If the database is a RAC database then each NODE can have different values for PROCESS parameter.

SQL> sho parameter spfile;

NAME                                           TYPE        VALUE

------------------------------------ ----------- ------------------------------

spfile                               string      +DATADG/DEVD/spfiledevd.ora

Increase the Process parameter (replace xxx with any higher value)

SQL> alter system set processes=XXX  scope=spfile;

System altered.

SQL> alter system set Sessions=XXX  scope=spfile;

System altered.

*** Bounce the database to take effect ***

If processes=x

sessions=x*1.1+5

transactions=sessions*1.1

If the database is running on pfile then follow below steps:

1. Edit the database init.ora

2. Locate and increase the processes parameter to a higher value.

3. Save the init.ora file

4. Stop and restart the database

5. Re-connect to the database instance

For more Refer:

Troubleshooting Guide - ORA-20: Maximum Number Of Processes (%S) Exceeded (Doc ID 1287854.1)