[Oracle]跨越 DBLINK 访问表时，数据缓存在何处的Data Buffer 中？

结论是存储在 remote 端，这其实也很好理解。在远端能高效率地计算，当然应当在远端完成缓存和检索。

■ Before query execution via DBLINK:

===========
DBLINK destination (remote side):

conn u2 / u2
create table tab002 as select * from dba_objects;

shu immediate
startup

select o.owner, o.object_name, o.object_type, s.buffer_pool, count (*) buffer
 from dba_objects o, v $ bh b, dba_segments s
 where b.objd = o.data_object_id
 and o.owner = 'U 2'
 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;

A record was not selected.

===========
Local side:

conn u3 / u3

select o.owner, o.object_name, o.object_type, s.buffer_pool, count (*) buffer
 from dba_objects o, v $ bh b, dba_segments s
 where b.objd = o.data_object_id
 and o.owner = 'U 2'
 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;

A record was not selected.

select o.owner, o.object_name, o.object_type, s.buffer_pool, count (*) buffer
 from dba_objects o, v $ bh b, dba_segments s
 where b.objd = o.data_object_id
 and o.owner = 'U3'
 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;

A record was not selected.

■ Query execution via DBLINK:

SQL> select count (*) from tab002 @ dbk;

COUNT (*)
----------
   69263

conn u3 / u3

select o.owner, o.object_name, o.object_type, s.buffer_pool, count (*) buffer
 from dba_objects o, v $ bh b, dba_segments s
 where b.objd = o.data_object_id
 and o.owner = 'U 2'
 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;

A record was not selected. <<<<<<<<<<< Cache has no related information

select o.owner, o.object_name, o.object_type, s.buffer_pool, count (*) buffer
 from dba_objects o, v $ bh b, dba_segments s
 where b.objd = o.data_object_id
 and o.owner = 'U3'
 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;

A record was not selected. <<<<<<<<<<< Cache has no related information

===========
DBLINK destination (remote side):

select o.owner, o.object_name, o.object_type, s.buffer_pool, count (*) buffer
 from dba_objects o, v $ bh b, dba_segments s
 where b.objd = o.data_object_id
 and o.owner = 'U 2'
 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
----------
U2
TAB 002
TABLE DEFAULT
    2042 ★ ★ <<<<<<<<<<<<<<<<<< data got into the cache.

select o.owner, o.object_name, o.object_type, s.buffer_pool, count (*) buffer
 from dba_objects o, v $ bh b, dba_segments s
 where b.objd = o.data_object_id
 and o.owner = 'U3'
 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;

A record was not selected.