统计信息知识点梳理-20200924-V1.0
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统计信息知识点梳理
-20200924-
V1.0
编号：
版本：
1.0
1 / 13
二零二零年九月
目录
1
Overview of Optimizer Statistics
...............................................................................1-5
1.1 Table statistics
..................................................................................................................1-5
1.1.1 Number of rows.....................................................................1-5
1.1.2 Number of blocks...................................................................1-5
1.1.3 Average row length................................................................1-5
1.2 Column statistics....................................................................................................................1-5
1.2.1 Number of distinct values (NDV) in column...........................1-5
1.2.2 Number of nulls in column.....................................................1-5
1.2.3 Data distribution (histogram)................................................1-5
1.2.4 Extended statistics................................................................1-5
1.3 Index statistics.......................................................................................................................1-5
1.3.1 Number of leaf blocks............................................................1-5
1.3.2 Levels....................................................................................1-5
1.3.3 Clustering factor....................................................................1-5
1.4 System statistics.....................................................................................................................1-5
1.4.1 I/O performance and utilization.............................................1-5
1.4.2 CPU performance and utilization...........................................1-6
2 Managing Automatic Optimizer Statistics Collection...........................................................2-7
2.1 Enabling and Disabling Automatic Optimizer Statistics Collection......................................2-7
2.2 Considerations When Gathering Statistics............................................................................2-7
2.2.1 When to Use Manual Statistics..............................................2-7
2.2.2 Restoring Previous Versions of Statistics...............................2-7
2.2.3 Locking Statistics...................................................................2-7
3 Gathering Statistics Manually................................................................................................3-8
3.1 Gathering Statistics with DBMS_STATS Procedures...........................................................3-8
3.1.1 Statistics Gathering Using Sampling.....................................3-8
3.1.2 Parallel Statistics Gathering...................................................3-8
3.1.3 Statistics on Partitioned Objects............................................3-8
3.1.4 Column Statistics and Histograms.........................................3-8
3.1.5 Extended Statistics................................................................3-8
3.1.6 MultiColumn Statistics...........................................................3-8
3.1.7 Expression Statistics..............................................................3-8
3.1.8 Determining Stale Statistics..................................................3-9
3.1.9 User-De:ned Statistics..........................................................3-9
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