因系統記憶體使用率過高，導致客戶端無法正常連線資料庫（在伺服器上sqlplus  / as sysdba可以登入，但sqlplus a/[email protected] as sysdba方式不可以登入）

現象如下：

C:\Users\Administrator>sqlplus system/[email protected]
SQL*Plus: Release 11.2.0.3.0 Production on 星期三 6月 15 15:21:59 2016
Copyright (c) 1982, 2011, Oracle.  All rights reserved.
ERROR:
ORA-12518: TNS: 監聽程式無法分發客戶機連線
請輸入使用者名稱:

Tnsname.ora檔案配置如下：

ORCL =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = WIN-MIRBE4NEBAU)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = orcl)
    )
  )
  
C:\Users\Administrator>tnsping orcl
TNS Ping Utility for 64-bit Windows: Version 11.2.0.3.0 - Production on 15-6月 - 2016 15:22:38
Copyright (c) 1997, 2011, Oracle.  All rights reserved.
已使用的引數檔案:
D:\app\Administrator\product\11.2.0\dbhome_1\network\admin\sqlnet.ora
已使用 TNSNAMES 介面卡來解析別名
嘗試連線 (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = WIN-MIRBE4NEBAU)(PORT
 = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = orcl)))
OK (10 毫秒)

檢查系統資源使用率如下：

參考ORA-12518 / TNS-12518 Troubleshooting (文件 ID 556428.1)：

a) Please add following parameter in listener.ora
INBOUND_CONNECT_TIMEOUT_LISTENER = 0
b) Add the following parameter to the sqlnet.ora file on the Database server side:
SQLNET.INBOUND_CONNECT_TIMEOUT = 0
The listener and database will need to be restarted after these changes.

重啟監聽及db後，客戶端可以正常連線資料庫。

SQL> conn system/[email protected]
已連線。