Oracle Cache表

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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>

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