DBMS_STATS比较复杂参数

最新推荐文章于 2024-07-02 11:30:00 发布

转载最新推荐文章于 2024-07-02 11:30:00 发布 · 130 阅读

本文详细介绍了Oracle数据库中直方图统计信息的收集方法及参数设置，包括不同直方图大小选项的作用，如何指定特定列进行直方图收集，以及如何根据不同需求选择收集范围。此外还介绍了统计信息收集的粒度选项与进一步的对象统计规范。

method_opt
Accepts:
FOR ALL [INDEXED | HIDDEN] COLUMNS [size_clause]
FOR COLUMNS [size clause] column|attribute [size_clause] [,column|attribute [size_clause]…]
size_clause is defined as size_clause := SIZE {integer | REPEAT | AUTO | SKEWONLY}

- integer : Number of histogram buckets. Must be in the range [1,254].
- REPEAT : Collects histograms only on the columns that already have histograms.
- AUTO : Oracle determines the columns to collect histograms based on data distribution and the workload of the columns.
- SKEWONLY : Oracle determines the columns to collect histograms based on the data distribution of the columns.

举例说明：
method_opt => ‘FOR COLUMNS size 254 object_id’ 收集objct_id列直方图
method_opt => ‘FOR COLUMNS size 1 object_id’ 删除object_id列直方图
method_opt => ‘for all columns size repeat’ 重新分析现有直方图
method_opt => ‘for all columns size auto’ oracle决定收集哪些列的直方图（需要设置table monitoring）
method_opt => ‘for all columns size skewonly’ oracle分析所有列的分布情况，生成直方图
method_opt => ‘FOR COLUMNS object_id size SKEWONLY’ 收集object_id列分布情况，生成直方图
method_opt => ‘FOR all INDEXED COLUMNS size SKEWONLY’ 收集index列分布情况，并生成直方图

granularity
Granularity of statistics to collect (only pertinent if the table is partitioned).
‘ALL’ – gathers all (subpartition, partition, and global) statistics
‘AUTO’- determines the granularity based on the partitioning type. This is the default value.
‘DEFAULT’ – gathers global and partition-level statistics. This option is obsolete, and while currently supported, it is included in the documentation for legacy reasons only. You should use the ‘GLOBAL AND PARTITION’ for this functionality. Note that the default value is now ‘AUTO’.
‘GLOBAL’ – gathers global statistics
‘GLOBAL AND PARTITION’ – gathers the global and partition level statistics. No subpartition level statistics are gathered even if it is a composite partitioned object.
‘PARTITION ‘- gathers partition-level statistics
‘SUBPARTITION’ – gathers subpartition-level statistics.

options
Further specification of which objects to gather statistics for:
GATHER: Gathers statistics on all objects in the schema.
GATHER AUTO: Gathers all necessary statistics automatically. Oracle implicitly determines which objects need new statistics, and determines how to gather those statistics. When GATHER AUTO is specified, the only additional valid parameters are ownname, stattab, statid, objlist and statown; all other parameter settings are ignored. Returns a list of processed objects.
GATHER STALE: Gathers statistics on stale objects as determined by looking at the *_tab_modifications views. Also, return a list of objects found to be stale.
GATHER EMPTY: Gathers statistics on objects which currently have no statistics. also, return a list of objects found to have no statistics.
LIST AUTO: Returns a list of objects to be processed with GATHER AUTO.
LIST STALE: Returns list of stale objects as determined by looking at the *_tab_modifications views.
LIST EMPTY: Returns list of objects which currently have no statistics.

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