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Oracle11新特性——SQL缓存结果集

  • 来源： IT168 作者： sevenleaf   2010-06-29/15:19

    •       SQL语句的缓存结果集功能是Oracle11g中最吸引我的一个新功能。
          DB_BUFFER只能缓存访问过的BLOCK，部分解决了物理读的问题，查询仍然需要大量的逻辑读。
          物化视图提供的是查询重写的功能，对于大部分的情况，只是简化了SQL的复杂度，即使是完全满足查询的条件，物化视图的扫描也是不可避免的。
          而缓存结果集——RESULT CACHE则截然不同，它缓存的是查询的结果。不在需要大量的逻辑读，不在需要任何的复杂计算，而是直接将已经缓存的结果返回。
          Oracle新增了两个HINT，RESULT_CACHE和NO_RESULT_CACHE。通过这两个提示，可以明确的指出下面的语句是否进行RESULT CACHE。
          Oracle还增加了几个初始化参数来管理RESULT CACHE功能，如：RESULT_CACHE_MODE、RESULT_CACHE_MAX_SIZE等。RESULT_CACHE_MAX_SIZE指明SGA中RESULT CACHE功能可以使用的最大的内存容量。如果这个参数设置为0，则关闭RESULT CACHE功能。RESULT_CACHE_MODE参数设置Oracle如何使用RESULT CACHE，该参数有三个值：MANUAL、AUTO、FORCE。后面会通过几个例子来说明三种情况的区别。
          Oracle提供了DBMS_RESULT_CACHE包来管理和维护RESULT CACHE。
          Oracle还新增了几个关于RESULT CACHE的系统视图，用户可以看到和RESULT CACHE相关的各种信息，视图包括：V$RESULT_CACHE_DEPENDENCY、V$RESULT_CACHE_MEMORY、V$RESULT_CACHE_OBJECTS和V$RESULT_CACHE_STATISTICS等。
          首先先看一下RESULT_CACHE所带来的性能提升：
    PHP code:--------------------------------------------------------------------------------
    SQL> create table t as select * from dba_objects;
    表已创建。
    SQL> set autot on
    SQL> set timing on
    SQL> select count(*) from t;
    COUNT(*)
    ----------
    68324
    已用时间: 00: 00: 00.12
    执行计划
    ----------------------------------------------------------
    Plan hash value: 2966233522
    -------------------------------------------------------------------
    | Id | Operation | Name | Rows | Cost (%CPU)| Time |
    -------------------------------------------------------------------
    | 0 | SELECT STATEMENT | | 1 | 282 (1)| 00:00:04 |
    | 1 | SORT AGGREGATE | | 1 | | |
    | 2 | TABLE ACCESS FULL| T | 52976 | 282 (1)| 00:00:04 |
    -------------------------------------------------------------------
    Note
    -----
    - dynamic sampling used for this statement
    统计信息
    ----------------------------------------------------------
    28 recursive calls
    0 db block gets
    1066 consistent gets
    1006 physical reads
    0 redo size
    338 bytes sent via SQL*Net to client
    377 bytes received via SQL*Net from client
    2 SQL*Net roundtrips to/from client
    0 sorts (memory)
    0 sorts (disk)
    1 rows processed
    SQL> select /*+ result_cache */ count(*) from t;
    COUNT(*)
    ----------
    68324
    已用时间: 00: 00: 00.21
    执行计划
    ----------------------------------------------------------
    Plan hash value: 2966233522
    ------------------------------------------------------------------------------------------
    | Id | Operation | Name | Rows | Cost (%CPU)| Time |
    ------------------------------------------------------------------------------------------
    | 0 | SELECT STATEMENT | | 1 | 282 (1)| 00:00:04 |
    | 1 | RESULT CACHE | 1t707xy2juqfq1xgx9dvy4bcqj | | | |
    | 2 | SORT AGGREGATE | | 1 | | |
    | 3 | TABLE ACCESS FULL| T | 52976 | 282 (1)| 00:00:04 |
    ------------------------------------------------------------------------------------------
    Result Cache Information (identified by operation id):
    ------------------------------------------------------
    1 - column-count=1; dependencies=(YANGTK.T); attributes=(single-row); name="select /*+ result_cac
    t"
    Note
    -----
    - dynamic sampling used for this statement
    统计信息
    ----------------------------------------------------------
    4 recursive calls
    0 db block gets
    1064 consistent gets
    0 physical reads
    0 redo size
    338 bytes sent via SQL*Net to client
    377 bytes received via SQL*Net from client
    2 SQL*Net roundtrips to/from client
    0 sorts (memory)
    0 sorts (disk)
    1 rows processed
    SQL> select /*+ result_cache */ count(*) from t;
    COUNT(*)
    ----------
    68324

    已用时间: 00: 00: 00.00

    执行计划
    ----------------------------------------------------------
    Plan hash value: 2966233522
    ------------------------------------------------------------------------------------------
    | Id | Operation | Name | Rows | Cost (%CPU)| Time |
    ------------------------------------------------------------------------------------------
    | 0 | SELECT STATEMENT | | 1 | 282 (1)| 00:00:04 |
    | 1 | RESULT CACHE | 1t707xy2juqfq1xgx9dvy4bcqj | | | |
    | 2 | SORT AGGREGATE | | 1 | | |
    | 3 | TABLE ACCESS FULL| T | 52976 | 282 (1)| 00:00:04 |
    ------------------------------------------------------------------------------------------
    Result Cache Information (identified by operation id):
    ------------------------------------------------------
    1 - column-count=1; dependencies=(YANGTK.T); attributes=(single-row); name="select /*+ result_cac
    t"
    Note
    -----
    - dynamic sampling used for this statement
    统计信息
    ----------------------------------------------------------
    0 recursive calls
    0 db block gets
    0 consistent gets
    0 physical reads
    0 redo size
    338 bytes sent via SQL*Net to client
    377 bytes received via SQL*Net from client
    2 SQL*Net roundtrips to/from client
    0 sorts (memory)
    0 sorts (disk)
    1 rows processe--------------------------------------------------------------------------------
          由于第二次执行SQL语句的时候使用了RESULT_CACHE提示，Oracle将这个查询的结果集记录在共享内存中，当第三次查询执行的时候，不需要进行任何的处理，而直接读取结果集，几乎没有任何的消耗，逻辑读为0，运行时间也几乎为0。
          下面简单说明一下RESULT_CACHE_MODE的三种模式下，缓存结果集是如何工作的。
          当参数值设置为MANUAL时，只有通过HINT明确提示的SQL才会读取缓存结果集。如果不加提示，那么Oracle不会利用已经缓存的结果。
    PHP code:--------------------------------------------------------------------------------
    SQL> alter session set result_cache_mode = manual;
    会话已更改。
    SQL> select /*+ result_cache */ object_name from t where object_name = 'DUAL';
    OBJECT_NAME
    -----------------------------------------------------------
    DUAL
    DUAL
    执行计划
    ----------------------------------------------------------
    Plan hash value: 1601196873
    -------------------------------------------------------------------------------------
    | Id | Operation | Name | Rows | Bytes |Cost (%CPU)| Time |
    --------------------------------------------------------------------------------------
    | 0 | SELECT STATEMENT | | 11 | 726 | 282 (1)| 00:00:04 |
    | 1 | RESULT CACHE |fhp10hrt50095fufmw3s75txcx| | | | |
    |* 2 | TABLE ACCESS FULL| T | 11 | 726 | 282 (1)| 00:00:04 |
    ---------------------------------------------------------------------------------
    Predicate Information (identified by operation id):
    ---------------------------------------------------
    2 - filter("OBJECT_NAME"='DUAL')
    Result Cache Information (identified by operation id):
    ------------------------------------------------------
    1 - column-count=1; dependencies=(YANGTK.T); parameters=(nls); name="select /*+ result_cache */ o
    ere object_name = 'DUAL'"
    Note
    -----
    - dynamic sampling used for this statement
    统计信息
    ----------------------------------------------------------
    28 recursive calls
    0 db block gets
    1067 consistent gets
    0 physical reads
    0 redo size
    366 bytes sent via SQL*Net to client
    377 bytes received via SQL*Net from client
    2 SQL*Net roundtrips to/from client
    0 sorts (memory)
    0 sorts (disk)
    2 rows processed
    SQL> select /*+ result_cache */ object_name from t where object_name = 'DUAL';
    OBJECT_NAME
    ------------------------------------------------------------
    DUAL
    DUAL
    执行计划
    ----------------------------------------------------------
    Plan hash value: 1601196873
    ------------------------------------------------------------------------------------------
    | Id | Operation | Name | Rows | Bytes |Cost (%CPU)| Time |
    -------------------------------------------------------------------------------------------
    | 0 | SELECT STATEMENT | | 11 | 726 | 282 (1)| 00:00:04 |
    | 1 | RESULT CACHE | fhp10hrt50095fufmw3s75txcx| | | | |
    |* 2 | TABLE ACCESS FULL| T | 11 | 726 | 282 (1)| 00:00:04 |
    -------------------------------------------------------------------------------------------
    Predicate Information (identified by operation id):
    ---------------------------------------------------
    2 - filter("OBJECT_NAME"='DUAL')
    Result Cache Information (identified by operation id):
    ------------------------------------------------------
    1 - column-count=1; dependencies=(YANGTK.T); parameters=(nls); name="select /*+ result_cache */ o
    ere object_name = 'DUAL'"
    Note
    -----
    - dynamic sampling used for this statement
    统计信息
    ----------------------------------------------------------
    0 recursive calls
    0 db block gets
    0 consistent gets
    0 physical reads
    0 redo size
    366 bytes sent via SQL*Net to client
    377 bytes received via SQL*Net from client
    2 SQL*Net roundtrips to/from client
    0 sorts (memory)
    0 sorts (disk)
    2 rows processed
    SQL> select object_name from t where object_name = 'DUAL';
    OBJECT_NAME
    -----------------------------------------------------------
    DUAL
    DUAL
    执行计划
    ----------------------------------------------------------
    Plan hash value: 1601196873
    --------------------------------------------------------------------------
    | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
    --------------------------------------------------------------------------
    | 0 | SELECT STATEMENT | | 11 | 726 | 282 (1)| 00:00:04 |
    |* 1 | TABLE ACCESS FULL| T | 11 | 726 | 282 (1)| 00:00:04 |
    --------------------------------------------------------------------------
    Predicate Information (identified by operation id):
    ---------------------------------------------------
    1 - filter("OBJECT_NAME"='DUAL')
    Note
    -----
    - dynamic sampling used for this statement
    统计信息
    ----------------------------------------------------------
    4 recursive calls
    0 db block gets
    1065 consistent gets
    0 physical reads
    0 redo size
    366 bytes sent via SQL*Net to client
    377 bytes received via SQL*Net from client
    2 SQL*Net roundtrips to/from client
    0 sorts (memory)
    0 sorts (disk)
    2 rows processed
    .--------------------------------------------------------------------------------
          当设置为MANUAL时，只有使用HINT的情况下，Oracle才会利用缓存结果集。而对于AUTO模式，Oracle如果发现缓冲结果集已经存在，那么就会使用。但是如果缓冲结果集不存在，Oracle并不会自动进行缓冲。只有使用HINT的情况下，Oracle才会将执行的结果集缓存。
    PHP code:--------------------------------------------------------------------------------
    SQL> alter session set result_cache_mode = auto;
    会话已更改。
    SQL> select object_name from t where object_name = 'DUAL';
    OBJECT_NAME
    ------------------------------
    DUAL
    DUAL
    执行计划
    ----------------------------------------------------------
    Plan hash value: 1601196873
    ------------------------------------------------------------------------------------------
    | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
    -----------------------------------------------------------------------------------------
    | 0 | SELECT STATEMENT | | 11 | 726 | 282 (1)| 00:00:04 |
    | 1 | RESULT CACHE |fhp10hrt50095fufmw3s75txcx| | | | |
    |* 2 | TABLE ACCESS FULL| T | 11 | 726 | 282 (1)| 00:00:04 |
    -------------------------------------------------------------------------------------------
    Predicate Information (identified by operation id):
    ---------------------------------------------------
    2 - filter("OBJECT_NAME"='DUAL')
    Result Cache Information (identified by operation id):
    ------------------------------------------------------
    1 - column-count=1; type=AUTO; dependencies=(YANGTK.T); parameters=(nls); name="select object_nam
    t_name = 'DUAL'"
    Note
    -----
    - dynamic sampling used for this statement

    统计信息
    ----------------------------------------------------------
    5 recursive calls
    0 db block gets
    53 consistent gets
    0 physical reads
    0 redo size
    366 bytes sent via SQL*Net to client
    377 bytes received via SQL*Net from client
    2 SQL*Net roundtrips to/from client
    0 sorts (memory)
    0 sorts (disk)
    2 rows processed
    SQL> select object_name from t where object_name = 'DUAL';
    OBJECT_NAME
    ------------------------------
    DUAL
    DUAL
    执行计划
    ----------------------------------------------------------
    Plan hash value: 1601196873
    -------------------------------------------------------------------------------------------------
    | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
    -------------------------------------------------------------------------------------------------
    | 0 | SELECT STATEMENT | | 11 | 726 | 282 (1)| 00:00:04 |
    | 1 | RESULT CACHE | fhp10hrt50095fufmw3s75txcx | | | | |
    |* 2 | TABLE ACCESS FULL| T | 11 | 726 | 282 (1)| 00:00:04 |
    -------------------------------------------------------------------------------------------------
    Predicate Information (identified by operation id):
    ---------------------------------------------------
    2 - filter("OBJECT_NAME"='DUAL')
    Result Cache Information (identified by operation id):
    ------------------------------------------------------
    1 - column-count=1; type=AUTO; dependencies=(YANGTK.T); parameters=(nls); name="select object_nam
    t_name = 'DUAL'"
    Note
    -----
    - dynamic sampling used for this statement

    统计信息
    ----------------------------------------------------------
    0 recursive calls
    0 db block gets
    0 consistent gets
    0 physical reads
    0 redo size
    366 bytes sent via SQL*Net to client
    377 bytes received via SQL*Net from client
    2 SQL*Net roundtrips to/from client
    0 sorts (memory)
    0 sorts (disk)
    2 rows processed
    SQL> select object_name from t where object_name = 'DBA_TABLES';
    OBJECT_NAME
    ------------------------------
    DBA_TABLES
    DBA_TABLES
    执行计划
    ----------------------------------------------------------
    Plan hash value: 1601196873
    -----------------------------------------------------------------------------------------------
    | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
    -----------------------------------------------------------------------------------------------
    | 0 | SELECT STATEMENT | | 11 | 726 | 282 (1)| 00:00:04 |
    | 1 | RESULT CACHE | 14buvcmfum6h9622vpkxm7sj2w| | | | |
    |* 2 | TABLE ACCESS FULL| T | 11 | 726 | 282 (1)| 00:00:04 |
    -----------------------------------------------------------------------------------------------
    Predicate Information (identified by operation id):
    ---------------------------------------------------
    2 - filter("OBJECT_NAME"='DBA_TABLES')

    Result Cache Information (identified by operation id):
    -----------------------------------------------------
    1 - column-count=1; type=AUTO; dependencies=(YANGTK.T); parameters=(nls); name="select object_nam
    t_name = 'DBA_TABLES'"
    Note
    -----
    - dynamic sampling used for this statement
    统计信息
    ----------------------------------------------------------
    4 recursive calls
    0 db block gets
    1065 consistent gets
    0 physical reads
    0 redo size
    372 bytes sent via SQL*Net to client
    377 bytes received via SQL*Net from client
    2 SQL*Net roundtrips to/from client
    0 sorts (memory)
    0 sorts (disk)
    2 rows processed
    SQL> select object_name from t where object_name = 'DBA_TABLES';
    OBJECT_NAME
    ------------------------------
    DBA_TABLES
    DBA_TABLES
    执行计划
    ----------------------------------------------------------
    Plan hash value: 1601196873
    -------------------------------------------------------------------------------------------------
    | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
    -------------------------------------------------------------------------------------------------
    | 0 | SELECT STATEMENT | | 11 | 726 | 282 (1)| 00:00:04 |
    | 1 | RESULT CACHE | 14buvcmfum6h9622vpkxm7sj2w | | | | |
    |* 2 | TABLE ACCESS FULL| T | 11 | 726 | 282 (1)| 00:00:04 |
    -------------------------------------------------------------------------------------------------
    Predicate Information (identified by operation id):
    ---------------------------------------------------
    2 - filter("OBJECT_NAME"='DBA_TABLES')

    Result Cache Information (identified by operation id):
    ------------------------------------------------------
    1 - column-count=1; type=AUTO; dependencies=(YANGTK.T); parameters=(nls); name="select object_nam
    t_name = 'DBA_TABLES'"
    Note
    -----
    - dynamic sampling used for this statement

    统计信息
    ----------------------------------------------------------
    0 recursive calls
    0 db block gets
    1012 consistent gets
    0 physical reads
    0 redo size
    372 bytes sent via SQL*Net to client
    377 bytes received via SQL*Net from client
    2 SQL*Net roundtrips to/from client
    0 sorts (memory)
    0 sorts (disk)
    2 rows processed
    .--------------------------------------------------------------------------------
          对比上面两种情况，由于第一个SQL的缓存结果集已经存在，Oracle采用了缓存结果集，而对于第二个SQL，Oracle是不会自动使用缓存结果集的。
    PHP code:--------------------------------------------------------------------------------
    SQL> select /*+ result_cache */ object_name from t where object_name = 'DBA_TABLES';
    OBJECT_NAME
    ------------------------------
    DBA_TABLES
    DBA_TABLES

    执行计划
    ----------------------------------------------------------
    Plan hash value: 1601196873
    -------------------------------------------------------------------------------------------------
    | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
    -------------------------------------------------------------------------------------------------
    | 0 | SELECT STATEMENT | | 11 | 726 | 282 (1)| 00:00:04 |
    | 1 | RESULT CACHE | 14buvcmfum6h9622vpkxm7sj2w | | | | |
    |* 2 | TABLE ACCESS FULL| T | 11 | 726 | 282 (1)| 00:00:04 |
    -------------------------------------------------------------------------------------------------
    Predicate Information (identified by operation id):
    ---------------------------------------------------
    2 - filter("OBJECT_NAME"='DBA_TABLES')

    Result Cache Information (identified by operation id):
    ------------------------------------------------------
    1 - column-count=1; dependencies=(YANGTK.T); parameters=(nls); name="select /*+ result_cache */ o
    ere object_name = 'DBA_TABLES'"
    Note
    -----
    - dynamic sampling used for this statement
    统计信息
    ----------------------------------------------------------
    4 recursive calls
    0 db block gets
    1065 consistent gets
    0 physical reads
    0 redo size
    372 bytes sent via SQL*Net to client
    377 bytes received via SQL*Net from client
    2 SQL*Net roundtrips to/from client
    0 sorts (memory)
    0 sorts (disk)
    2 rows processed
    SQL> select object_name from t where object_name = 'DBA_TABLES';
    OBJECT_NAME
    ------------------------------
    DBA_TABLES
    DBA_TABLES
    执行计划
    ----------------------------------------------------------
    Plan hash value: 1601196873
    -------------------------------------------------------------------------------------------------
    | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
    -------------------------------------------------------------------------------------------------
    | 0 | SELECT STATEMENT | | 11 | 726 | 282 (1)| 00:00:04 |
    | 1 | RESULT CACHE | 14buvcmfum6h9622vpkxm7sj2w | | | | |
    |* 2 | TABLE ACCESS FULL| T | 11 | 726 | 282 (1)| 00:00:04 |
    -------------------------------------------------------------------------------------------------
    Predicate Information (identified by operation id):
    ---------------------------------------------------
    2 - filter("OBJECT_NAME"='DBA_TABLES')

    Result Cache Information (identified by operation id):
    ------------------------------------------------------
    1 - column-count=1; type=AUTO; dependencies=(YANGTK.T); parameters=(nls); name="select object_nam
    t_name = 'DBA_TABLES'"
    Note
    -----
    - dynamic sampling used for this statement

    统计信息
    ----------------------------------------------------------
    0 recursive calls
    0 db block gets
    0 consistent gets
    0 physical reads
    0 redo size
    372 bytes sent via SQL*Net to client
    377 bytes received via SQL*Net from client
    2 SQL*Net roundtrips to/from client
    0 sorts (memory)
    0 sorts (disk)
    2 rows processed
    .--------------------------------------------------------------------------------
          当使用HINT后，结果集被缓存，随后的相同的查询就会使用缓存的结果集。
          对于FORCE参数，顾名思义，就是会对所有的SQL进行缓存，除非明确使用NO_RESULT_CACHE提示：
    PHP code:--------------------------------------------------------------------------------
    SQL> alter session set result_cache_mode = force;
    会话已更改。
    SQL> select object_name from t where object_name = 'DBA_VIEWS';
    OBJECT_NAME
    ------------------------------
    DBA_VIEWS
    DBA_VIEWS
    执行计划
    ----------------------------------------------------------
    Plan hash value: 1601196873
    -------------------------------------------------------------------------------------------------
    | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
    -------------------------------------------------------------------------------------------------
    | 0 | SELECT STATEMENT | | 11 | 726 | 282 (1)| 00:00:04 |
    | 1 | RESULT CACHE | bdkgz2jxpb7tc8pkwn478qt3p0 | | | | |
    |* 2 | TABLE ACCESS FULL| T | 11 | 726 | 282 (1)| 00:00:04 |
    -------------------------------------------------------------------------------------------------
    Predicate Information (identified by operation id):
    ---------------------------------------------------
    2 - filter("OBJECT_NAME"='DBA_VIEWS')
    Result Cache Information (identified by operation id):
    ------------------------------------------------------
    1 - column-count=1; dependencies=(YANGTK.T); parameters=(nls); name="select object_name from t wh
    BA_VIEWS'"
    Note
    -----
    - dynamic sampling used for this statement
    统计信息
    ----------------------------------------------------------
    5 recursive calls
    0 db block gets
    1065 consistent gets
    0 physical reads
    0 redo size
    371 bytes sent via SQL*Net to client
    377 bytes received via SQL*Net from client
    2 SQL*Net roundtrips to/from client
    0 sorts (memory)
    0 sorts (disk)
    2 rows processed
    SQL> select object_name from t where object_name = 'DBA_VIEWS';
    OBJECT_NAME
    ------------------------------
    DBA_VIEWS
    DBA_VIEWS
    执行计划
    ----------------------------------------------------------
    Plan hash value: 1601196873
    -------------------------------------------------------------------------------------------------
    | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
    -------------------------------------------------------------------------------------------------
    | 0 | SELECT STATEMENT | | 11 | 726 | 282 (1)| 00:00:04 |
    | 1 | RESULT CACHE | bdkgz2jxpb7tc8pkwn478qt3p0 | | | | |
    |* 2 | TABLE ACCESS FULL| T | 11 | 726 | 282 (1)| 00:00:04 |
    -------------------------------------------------------------------------------------------------
    Predicate Information (identified by operation id):
    ---------------------------------------------------
    2 - filter("OBJECT_NAME"='DBA_VIEWS')
    Result Cache Information (identified by operation id):
    ------------------------------------------------------
    1 - column-count=1; dependencies=(YANGTK.T); parameters=(nls); name="select object_name from t wh
    BA_VIEWS'"
    Note
    -----
    - dynamic sampling used for this statement
    统计信息
    ----------------------------------------------------------
    0 recursive calls
    0 db block gets
    0 consistent gets
    0 physical reads
    0 redo size
    371 bytes sent via SQL*Net to client
    377 bytes received via SQL*Net from client
    2 SQL*Net roundtrips to/from client
    0 sorts (memory)
    0 sorts (disk)
    2 rows processed
    SQL> select /*+ no_result_cache */ object_name from t where object_name = 'DBA_VIEWS';
    OBJECT_NAME
    ------------------------------
    DBA_VIEWS
    DBA_VIEWS
    执行计划
    ----------------------------------------------------------
    Plan hash value: 1601196873
    --------------------------------------------------------------------------
    | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
    --------------------------------------------------------------------------
    | 0 | SELECT STATEMENT | | 11 | 726 | 282 (1)| 00:00:04 |
    |* 1 | TABLE ACCESS FULL| T | 11 | 726 | 282 (1)| 00:00:04 |
    --------------------------------------------------------------------------
    Predicate Information (identified by operation id):
    ---------------------------------------------------
    1 - filter("OBJECT_NAME"='DBA_VIEWS')
    Note
    -----
    - dynamic sampling used for this statement
    统计信息
    ----------------------------------------------------------
    4 recursive calls
    0 db block gets
    1065 consistent gets
    0 physical reads
    0 redo size
    371 bytes sent via SQL*Net to client
    377 bytes received via SQL*Net from client
    2 SQL*Net roundtrips to/from client
    0 sorts (memory)
    0 sorts (disk)
    2 rows processed
    .--------------------------------------------------------------------------------


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