[Oracle]跨DBLINK的JOIN查询的数据库缓存问题15783452141

客户问到跨DBLINK，结合本地表和远端表的时候，数据在哪一边 的 Data Buffer 缓存。

测试的结果是：本地表在本地缓存，远端表在远端缓存。

####Testcase-0929-10

本地数据库：     远端数据库：
TABXXX           TABYYY

=============
本地数据库：

conn user003/user003

create table TABXXX(id integer, val varchar2(3));

insert into TABXXX values(1,'100');
insert into TABXXX values(2,'200');
insert into TABXXX values(3,'300');
commit;

=============
远端数据库：

conn user002/user002

create table TABYYY(id integer, val varchar2(3));

insert into TABYYY values(2,'200');
insert into TABYYY values(3,'300');
insert into TABYYY values(4,'400');
commit;

=============
本地数据库：
shu immediate
startup

conn user003/user003

create public database link dbk connect to user002 identified by user002 using 'remote';

查询前检查Buffer:

conn / as sysdba

select o.owner,o.object_name,o.object_type,s.buffer_pool,count(*) buffers
  from dba_objects o,v$bh b,dba_segments s
  where b.objd=o.data_object_id
  and o.owner = 'user002'
  and o.object_name=s.segment_name
  and o.object_type=s.segment_type
  group by o.owner,o.object_name,o.object_type,o.status,s.buffer_pool
  order by buffers;

select o.owner,o.object_name,o.object_type,s.buffer_pool,count(*) buffers
  from dba_objects o,v$bh b,dba_segments s
  where b.objd=o.data_object_id
  and o.owner = 'user003'
  and o.object_name=s.segment_name
  and o.object_type=s.segment_type
  group by o.owner,o.object_name,o.object_type,o.status,s.buffer_pool
  order by buffers;

=============
远端数据库：

查询前检查Buffer:

shu immediate
startup

conn / as sysdba

select o.owner,o.object_name,o.object_type,s.buffer_pool,count(*) buffers
  from dba_objects o,v$bh b,dba_segments s
  where b.objd=o.data_object_id
  and o.owner = 'user002'
  and o.object_name=s.segment_name
  and o.object_type=s.segment_type
  group by o.owner,o.object_name,o.object_type,o.status,s.buffer_pool
  order by buffers;

select o.owner,o.object_name,o.object_type,s.buffer_pool,count(*) buffers
  from dba_objects o,v$bh b,dba_segments s
  where b.objd=o.data_object_id
  and o.owner = 'user003'
  and o.object_name=s.segment_name
  and o.object_type=s.segment_type
  group by o.owner,o.object_name,o.object_type,o.status,s.buffer_pool
  order by buffers;

=============
本地数据库：

执行查询：

conn user003/user003

select a.id,b.value from TABXXX a, TABYYY@dbk b where a.id=b.id;

查询后检查缓存:　　<<<<<<<<<<<<<<<<<<　本地表在本地缓存，本地没有远端表的缓存内容

conn / as sysdba

　　
select o.owner,o.object_name,o.object_type,s.buffer_pool,count(*) buffers
 from dba_objects o,v$bh b,dba_segments s
 where b.objd=o.data_object_id
 and o.owner = 'user002'
 and o.object_name=s.segment_name
 and o.object_type=s.segment_type
 group by o.owner,o.object_name,o.object_type,o.status,s.buffer_pool
 order by buffers;

no records found

select o.owner,o.object_name,o.object_type,s.buffer_pool,count(*) buffers
 from dba_objects o,v$bh b,dba_segments s
 where b.objd=o.data_object_id
 and o.owner = 'user003'
 and o.object_name=s.segment_name
 and o.object_type=s.segment_type
 group by o.owner,o.object_name,o.object_type,o.status,s.buffer_pool
 order by buffers;

OWNER
--------------------------------------------------------------------------------
OBJECT_NAME
--------------------------------------------------------------------------------
OBJECT_TYPE                                               BUFFER_POOL
--------------------------------------------------------- ---------------------
  BUFFERS
----------
user003
TABXXX
TABLE                                                     DEFAULT
        7

SQL>

=============
远端数据库：

查询后检查缓存:                      <<<<<<<<<<<<<<<<<<　远端表在远端缓存，远端数据库那边，没有本地表的缓存内容

conn / as sysdba

select o.owner,o.object_name,o.object_type,s.buffer_pool,count(*) buffers
 from dba_objects o,v$bh b,dba_segments s
 where b.objd=o.data_object_id
 and o.owner = 'user002'
 and o.object_name=s.segment_name
 and o.object_type=s.segment_type
 group by o.owner,o.object_name,o.object_type,o.status,s.buffer_pool
 order by buffers;

OWNER
--------------------------------------------------------------------------------
OBJECT_NAME
--------------------------------------------------------------------------------
OBJECT_TYPE                                               BUFFER_POOL
--------------------------------------------------------- ---------------------
  BUFFERS
----------
user002
TABYYY
TABLE                                                     DEFAULT
       14

SQL>

select o.owner,o.object_name,o.object_type,s.buffer_pool,count(*) buffers
 from dba_objects o,v$bh b,dba_segments s
 where b.objd=o.data_object_id
 and o.owner = 'user003'
 and o.object_name=s.segment_name
 and o.object_type=s.segment_type
 group by o.owner,o.object_name,o.object_type,o.status,s.buffer_pool
 order by buffers;

no records found