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  • [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.

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  • 原文地址:https://www.cnblogs.com/gaojian/p/7575226.html
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