问题描述：客户端连接数据库报错
ORA-12516: TNS: 监听程序无法找到匹配协议栈的可用句柄
解决过程：
1。查看当前会话数、processes和sessions值，发现session数和2个参数的值已经非常逼近
SQL*Plus: Release 10.2.0.1.0 - Production on 星期一 10月 9 15:50:21 2006
SQL> conn / as sysdba
已连接。
SQL> select count(*) from v＄session;
COUNT(*)
----------
45
SQL> show parameter processes
NAME TYPE VALUE
------------------------------------ ----------- ----------------------
aq_tm_processes integer 0
db_writer_processes integer 1
gcs_server_processes integer 0
job_queue_processes integer 10
log_archive_max_processes integer 2
processes integer 50
SQL> show parameter sessions
NAME TYPE VALUE
------------------------------------ ----------- ----------------------
java_max_sessionspace_size integer 0
java_soft_sessionspace_limit integer 0
license_max_sessions integer 0
license_sessions_warning integer 0
logmnr_max_persistent_sessions integer 1
sessions integer 60
shared_server_sessions integer
2。修改processes和sessions值
SQL> alter system set processes=300 scope=spfile;
系统已更改。
SQL> alter system set sessions=300 scope=spfile;
系统已更改。
3。查看processes和sessions参数，但更改并未生效
SQL> show parameter processes
NAME TYPE VALUE
------------------------------------ ----------- ----------------------
aq_tm_processes integer 0
db_writer_processes integer 1
gcs_server_processes integer 0
job_queue_processes integer 10
log_archive_max_processes integer 2
processes integer 50
SQL> show parameter sessions
NAME TYPE VALUE
------------------------------------ ----------- ----------------------
java_max_sessionspace_size integer 0
java_soft_sessionspace_limit integer 0
license_max_sessions integer 0
license_sessions_warning integer 0
logmnr_max_persistent_sessions integer 1
sessions integer 60
shared_server_sessions integer
4。重启数据库，使更改生效
SQL> shutdown immediate
SQL> startup
SQL> show parameter processes
NAME TYPE VALUE
------------------------------------ ----------- ----------------------
aq_tm_processes integer 0
db_writer_processes integer 1
gcs_server_processes integer 0
job_queue_processes integer 10
log_archive_max_processes integer 2
processes integer 300
SQL> show parameter sessions
NAME TYPE VALUE
------------------------------------ ----------- ---