buffer pool latch和cache buffers chains latch

<pre name="code" class="sql">buffer pool latch 是用来保护buffer pool的
每个buffer pool有一个buffer pool latch保护
SQL> select addr,LATCH#,LEVEL#,CHILD#,NAME from v$latch_children where name='buffer pool';

ADDR	     LATCH#	LEVEL#	   CHILD# NAME
-------- ---------- ---------- ---------- ----------------------------------------------------------------
2CD760A8	146	     1		8 buffer pool
2CD75F78	146	     1		7 buffer pool
2CD75E48	146	     1		6 buffer pool
2CD75D18	146	     1		5 buffer pool
2CD75BE8	146	     1		4 buffer pool
2CD75AB8	146	     1		3 buffer pool
2CD75988	146	     1		2 buffer pool
2CD75858	146	     1		1 buffer pool

已选择8行。


cache buffers chains latch是用来保护 hash  buckets:


SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ
  FROM x$ksppi x, x$ksppcv y
 WHERE x.inst_id = USERENV('Instance')
   AND y.inst_id = USERENV('Instance')
   AND x.indx = y.indx
   AND x.ksppinm LIKE '%_db_block_hash%'  2    3    4    5    6  ;


NAME       VALUE DESCRIB
------------------------------ ---------- ------------------------------
_db_block_hash_buckets       16384 Number of database block hash  buckets


_db_block_hash_latches       1024 Number of database block hash  Latches


可以用下面查询计算cache buffers chains latch的数量:
SQL> select count(*) from v$latch_children a,v$latchname b where a.latch#=b.latch# and b.name='cache buffers chains';


  COUNT(*)
----------
      1024


根据我们的查询，那么一个cache buffers chains latch 平均下来要管理
Select 16384/1024 from dual 16个块.