【IT168 技术文档】
前面讨论了RECYCLE池的CACHE特点，这篇文章简单描述一下，如果在RECYCLE池中设置了CACHE选项，会产生什么效果。
不过，这种情况一般并不常见，对于放到RECYCLE池的对象，本来就是认为缓存在以后很少或不再使用。所以，很少会对RECYCLE池中的对象设置CACHE选项。不过如果希望对RECYCLE池中的对象再设置优先级的话，CACHE选项还是有点作用的。
首先，清掉RECYCLE池。
SQL> ALTER TABLESPACE NDMAIN OFFLINE;
Tablespace altered.
SQL> ALTER TABLESPACE NDMAIN ONLINE;
Tablespace altered.
利用T表将RECYCLE填满：
SQL> SELECT COUNT(*) FROM T;
COUNT(*)
----------
334022
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
9667 consistent gets
9657 physical reads
0 redo size
381 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
SQL> COL OBJECT_NAME FORMAT A30
SQL> SELECT OBJECT_NAME, A.STATUS, COUNT(*)
2 FROM V$BH A, USER_OBJECTS B
3 WHERE A.OBJD = B.OBJECT_ID
4 AND OBJECT_NAME IN ('T', 'T2', 'T3', 'IND_T_NAME')
5 GROUP BY OBJECT_NAME, A.STATUS;
OBJECT_NAME STATU COUNT(*)
------------------------------ ----- ----------
T xcur 8096
SQL> SELECT COUNT(*) FROM T2;
COUNT(*)
----------
167011
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
4839 consistent gets
4829 physical reads
0 redo size
381 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
SQL> SELECT OBJECT_NAME, A.STATUS, COUNT(*)
2 FROM V$BH A, USER_OBJECTS B
3 WHERE A.OBJD = B.OBJECT_ID
4 AND OBJECT_NAME IN ('T', 'T2', 'T3', 'IND_T_NAME')
5 GROUP BY OBJECT_NAME, A.STATUS;
OBJECT_NAME STATU COUNT(*)
------------------------------ ----- ----------
T xcur 8079
T2 xcur 17
SQL> SELECT COUNT(*) FROM T2;
COUNT(*)
----------
167011
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
4839 consistent gets
4828 physical reads
0 redo size
381 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
SQL> SELECT OBJECT_NAME, A.STATUS, COUNT(*)
2 FROM V$BH A, USER_OBJECTS B
3 WHERE A.OBJD = B.OBJECT_ID
4 AND OBJECT_NAME IN ('T', 'T2', 'T3', 'IND_T_NAME')
5 GROUP BY OBJECT_NAME, A.STATUS;
OBJECT_NAME STATU COUNT(*)
------------------------------ ----- ----------
T xcur 8079
T2 xcur 17
对于前面提到的RECYCLE池的算法，T2的数据不会进入到缓冲区内。
