11G引入了延遲密碼驗證，在輸入錯誤的密碼后，后續如果還是采用錯誤的密碼登陸，將會導致密碼延遲驗證，
而且會導致失敗登陸延長。如下：

[oracle@db2server ~]$ time echo "select sysdate from dual;" | sqlplus -s scott/tige 1> /dev/null 2>&1

real ? ?0m0.160s
user ? ?0m0.003s
sys ? ? 0m0.066s
[oracle@db2server ~]$ time echo "select sysdate from dual;" | sqlplus -s scott/tige 1> /dev/null 2>&1

real ? ?0m0.175s
user ? ?0m0.003s
sys ? ? 0m0.065s
[oracle@db2server ~]$ time echo "select sysdate from dual;" | sqlplus -s scott/tige 1> /dev/null 2>&1

real ? ?0m0.185s
user ? ?0m0.013s
sys ? ? 0m0.060s
[oracle@db2server ~]$ time echo "select sysdate from dual;" | sqlplus -s scott/tige 1> /dev/null 2>&1

real ? ?0m1.306s
user ? ?0m0.040s
sys ? ? 0m0.088s
[oracle@db2server ~]$ time echo "select sysdate from dual;" | sqlplus -s scott/tige 1> /dev/null 2>&1

real ? ?0m2.176s
user ? ?0m0.006s
sys ? ? 0m0.073s
[oracle@db2server ~]$ time echo "select sysdate from dual;" | sqlplus -s scott/tige 1> /dev/null 2>&1

real ? ?0m3.187s
user ? ?0m0.003s
sys ? ? 0m0.074s
[oracle@db2server ~]$ time echo "select sysdate from dual;" | sqlplus -s scott/tige 1> /dev/null 2>&1

real ? ?0m4.162s
user ? ?0m0.003s
sys ? ? 0m0.054s
[oracle@db2server ~]$ time echo "select sysdate from dual;" | sqlplus -s scott/tige 1> /dev/null 2>&1

real ? ?0m5.302s
user ? ?0m0.004s
sys ? ? 0m0.077s
[oracle@db2server ~]$ time echo "select sysdate from dual;" | sqlplus -s scott/tige 1> /dev/null 2>&1

real ? ?0m6.602s
user ? ?0m0.007s
sys ? ? 0m0.075s

可以看到從第三次開始，后續的每次登陸導致密碼延遲1秒左右。

如果有多個會話同時登陸，將會導致會話HANG住，出現一些LATCH的競爭。

可以通過如下事件來屏蔽密碼的延遲驗證。

ALTER SYSTEM SET EVENT = '28401 TRACE NAME CONTEXT FOREVER, LEVEL 1' SCOPE = SPFILE

[oracle@db2server ~]$ oerr ora 28401
28401, 00000, "Event to disable delay after three failed login attempts"
// *Document: NO
// *Cause: N/A
// *Action: Set this event in your environment to disable the login delay?
// ? ? ? ? ?which will otherwise take place after three failed login attempts.
// *Note: THIS IS NOT A USER ERROR NUMBER/MESSAGE. THIS DOES NOT NEED TO BE
// ? ? ? ?TRANSLATED OR DOCUMENTED.

總結

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