latch：row cache objects

latch：row cache objects


当涉及到数据字典(dc)的操作时，就需要首先获得这个latch。例如生成执行计划时候，可能涉及直方图，那么就会涉及到相关dc信息。

该latch的相关参数：
P1 = Latch address 
P2 = Latch number 
P3 = Tries

根据p1raw可以定位到是在等待什么类型的dc：
SELECT 
        kqrsttxt PARAMETER, 
-- kqrstcid CACHE#, 
        kqrstcln "Lchild#", 
        kqrstgrq "DCGets", 
        l.gets   "LGets", 
        l.misses "Misses"
  FROM X$KQRST, V$LATCH_CHILDREN l
 WHERE l.addr='&P1RAW'
   and l.child#=KQRSTCLN
 ORDER BY 1,2



SQL> SELECT  distinct
        a.kqrsttxt  "PARAMETER", 
        a.kqrstcln  "Lchild#", 
        a.kqrstgrq  "DCGets", 
        b.gets   "LGets", 
        b.misses  "Misses"
  FROM X$KQRST a ,
  V$LATCH_CHILDREN b
 WHERE a.kqrsttxt like 'dc%'
   and b.child#=a.KQRSTCLN
 ORDER BY 1,2
   2    3    4    5    6    7    8    9   10   11   12  ;

PARAMETER			    Lchild#	DCGets	    LGets     Misses
-------------------------------- ---------- ---------- ---------- ----------
dc_awr_control				 47	    32		0	   0
dc_awr_control				 47	    32		5	   0
dc_awr_control				 47	    32	       12	   0
dc_awr_control				 47	    32	       45	   0
dc_awr_control				 47	    32	       97	   0
dc_awr_control				 47	    32	      396	   0
dc_awr_control				 47	    32	     1015	   0
dc_constraints				 11	     0		0	   0