當刪除oracle資料庫user時發生row cache lock 等待事件

在oracle資料庫中做的動作如下:

drop user abc; hang住，等待事件為 row cache lock

Hanganalyze   顯示

===============================================================================
 
Chains most likely to have caused the hang:
 [a] Chain 1 Signature: 'enq: TT - contention'<='row cache lock' (cycle)
  Chain 1 Signature Hash: 0x4a0d0d64
 [b] Chain 2 Signature: 'row cache lock'<='row cache lock' (cycle)
  Chain 2 Signature Hash: 0x75bdd0c
 [c] Chain 3 Signature: 'row cache lock'<='row cache lock' (cycle)
  Chain 3 Signature Hash: 0x75bdd0c
 
===============================================================================
Cycles:
 
-------------------------------------------------------------------------------
Chain 1:
-------------------------------------------------------------------------------
  Oracle session identified by:
  {
  instance: 1 (uouk2oas.uouk2oas1)
  os id: 15866
  process id: 197, oracle@uklpdufms01a (DW05)
  session id: 1193
  session serial #: 29877
  }
  is waiting for 'row cache lock' with wait info:
  {
  p1: 'cache id'=0xa
  p2: 'mode'=0x0
  p3: 'request'=0x3
  time in wait: 1.731862 sec
  heur. time in wait: 1871 min 58 sec
  timeout after: 1.268138 sec
  wait id: 489490
  blocking: 6 sessions
  current sql: BEGIN
  SYS.KUPW$WORKER.MAIN('SYS_IMPORT_FULL_08', 'SYS', 0); >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
 END;

impdp 匯入資料操作阻止了drop user 的操作，

解決方法:

1:  取消impdp導數操作

2：重新執行drop user操作