row cache lock

SQL> col name format a30
SQL> select * from (select SAMPLE_TIME,
       SESSION_ID,  
       NAME,  
       P1,  
       P2,  
       P3,
       ash.BLOCKING_SESSION  
  from v$active_session_history ash, v$event_name enm  
 where ash.event# = enm.event#
 and enm.NAME='row cache lock')
 where rownum<10;  2    3    4    5    6    7    8    9   10   11  

SAMPLE_TIME								    SESSION_ID NAME				      P1	 P2	    P3 

BLOCKING_SESSION
--------------------------------------------------------------------------- ---------- ------------------------------ ---------- ---------- ---------- -----

-----------
15-APR-14 07.48.08.840 PM							    22 row cache lock			      13	  0	     5
15-APR-14 07.45.49.883 PM							  1159 row cache lock			      13	  0	     5
15-APR-14 07.44.12.569 PM							    25 row cache lock			      13	  0	     5

ROW CACHE LOCK等待事件是一个共享池相关的等待事件。是由于对于字典缓冲的访问造成的。
P1 – Cache Id
P2 – Mode Held
P3 – Mode Requested

SQL查询
--查询row cache lock等待
select *  from v$session_wait where wait_class = 'row cache lock';
 
--查询rowcache 名称
select * from v$rowcache where cache# = &p1;


DC_SEQUENCES
Check for appropriate caching of sequences for the application requirements.

DC_USERS
Deadlock and resulting “WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK!” can occur if a session issues a GRANT to a user, and that user is in the process of 

logging on to the database.

DC_SEGMENTS
This is likely to be down to segment allocation. Identify what the session holding the enqueue is doing and use errorstacks to diagnose.

DB_ROLLBACK_SEGMENTS
This is due to rollback segment allocation. Just like dc_segments,identify what is holding the enqueue and also generate errorstacks. Remember that on a 

multi-node system (RAC) the holder may be on another node and so multiple systemstates from each node will be required.

DC_AWR_CONTROL
This enqueue is related to control of the Automatic Workload Repository. As such any operation manipulating the repository may hold this so look for 

processes blocking these.

SQL> select a.cache#,a.PARAMETER from v$rowcache a where cache# =13;

    CACHE# PARAMETER
---------- --------------------------------
	13 dc_sequences