Oracle Cache 表（转载boypoo博客）

在一个中项目用到cache 表，转载记录一下。


一、对于普通表的cache方法：
SQL> conn test/test 已连接。
SQL> alter table t1 storage (buffer_pool keep) cache;
表已更改。
查询普通表是否已经被cache：
  

SQL> select table_name,cache,buffer_pool from user_TABLES; TABLE_NAME                     CACHE      BUFFER_ ------------------------------ ---------- ------- T1                                 Y      KEEP

二、对于普通LOB类型的segment的cache方法

SQL> desc t2
名称 是否为空? 类型
---------------------------------------- -------- ----------------------------
ID NUMBER
C2 CLOB
SQL> alter table t2 modify lob(c2) (storage (buffer_pool keep) cache);
表已更改。

三、对基于CLOB类型的对象的cache方法
 

SQL> desc lob1
名称 是否为空? 类型
----------------------------------------- -------- --------------- ID NUMBER
C1 XMLTYPE
SQL> alter table lob1 modify lob(c1.xmldata) (storage (buffer_pool keep) cache);
表已更改。

那么，怎么测试lob segment是否被cache了呢?

来看看oracle给我的回复:

Hi Frank,

To verify which buffer pool is used by a lob segment query dba_segments,

See below test case

SQL> create table test(name varchar2(10), address clob);

Table created.

SQL> select table_name,cache,buffer_pool from user_TABLES;

TABLE_NAME CACHE BUFFER_
------------------------------ ----- -------
TEST N DEFAULT


SQL> alter table test modify lob(address) (storage (buffer_pool keep) nocache);

Table altered.

SQL> select table_name,cache,buffer_pool from user_TABLES;

TABLE_NAME CACHE BUFFER_
------------------------------ ----- -------
TEST N DEFAULT

SQL> select segment_name,segment_type,buffer_pool from user_segments;

SEGMENT_NAME
--------------------------------------------------------------------------------
SEGMENT_TYPE BUFFER_
------------------ -------
TEST
TABLE DEFAULT

SYS_IL0000123006C00002$$
LOBINDEX KEEP

SYS_LOB0000123006C00002$$
LOBSEGMENT KEEP


SQL> select column_name,segment_name from user_lobs;

COLUMN_NAME
--------------------------------------------------------------------------------
SEGMENT_NAME
------------------------------
ADDRESS
SYS_LOB0000123006C00002$$


SQL>

Thus you can see the lob segment SYS_LOB0000123006C00002$$ is mapped to clob column ad
dress and is using
keep buffer pool as expected.

User_objects will display results for object as a whole not for individual columns.

See below, we need to alter the complete table to use keep buffer_pool and user_tables will then
display results as expected.

SQL> alter table test storage (buffer_pool keep);

Table altered.

SQL> select table_name,cache,buffer_pool from user_TABLES;

TABLE_NAME CACHE BUFFER_
------------------------------ ----- -------
TEST N KEEP

SQL>