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  • OCP-1Z0-052-V8.02-41题

    41. You have recently collected statistics on certain objects of a schema in your database. But you

    observe suboptimal execution plans for the queries on these objects after two days of statistics collection.

    The optimizer statistics retention period is set to its default value. 

    Which action would help to use the previous set of statistics on the objects?

    A.Restore statistics from statistics history.

    B.Reduce the optimizer statistics retention period by 2 days.

    C.Set the OPTIMIZER_PENDING_STATISTICS parameter to TRUE.

    D.Reduce the Automatic Workload Repository (AWR) retention period by 2 days.

    Answer: A  
    答案解析:
    A,正确,可以从统计信息的历史信息恢复统计信息。如下面这个储存过程。

    RESTORE_TABLE_STATS Procedure

    This procedure restores statistics of a table as of a specified timestamp (as_of_timestamp). The procedure will restore statistics of associated indexes and columns as well. If the table statistics were locked at the specified timestamp the procedure will lock the statistics. The procedure will not restore user defined statistics.

    Syntax

    DBMS_STATS.RESTORE_TABLE_STATS (
       ownname                   VARCHAR2,
       tabname                   VARCHAR2,
       as_of_timestamp           TIMESTAMP WITH TIME ZONE,
       restore_cluster_index     BOOLEAN DEFAULT FALSE,
       force                     BOOLEAN DEFAULT FALSE,
       no_invalidate             BOOLEAN DEFAULT to_no_invalidate_type
                                                        (GET_PARAM('NO_INVALIDATE')));


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  • 原文地址:https://www.cnblogs.com/hzcya1995/p/13316539.html
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