Oracle 视图 DBA_HIGH_WATER_MARK_STATISTICS 官方解释，作用，如何使用详细说明
本站中文解释
Oracle视图DBA_HIGH_WATER_MARK_STATISTICS提供了High water mark（高水位线）的状况信息，它是一种分析提供占用空间和行访问频率的机制，一般使用于确定表和索引的内存空间构成。
使用方法：
1. 首先查询表的DBA_HIGH_WATER_MARK_STATISTICS：
SELECT * FROM DBA_HIGH_WATER_MARK_STATISTICS WHERE TABLE_NAME = ‘example_table’;
2. 通过DBA_HIGH_WATER_MARK_STATISTICS对需要分析的表指定索引：
SELECT * FROM DBA_HIGH_WATER_MARK_STATISTICS WHERE TABLE_NAME = ‘example_table’ AND INDEX_NAME = ‘example_index’;
3. 然后根据查询的统计数据确定表和索引的内存空间使用：
TABLE_NAME：指定的表
BLOCKS_ALLOCATED：分配给表的块数
BLOCKS_HIGH_WTR_MARK：分配的最高水位的块数
ROWS_HIGH_WTR_MARK：在最高水位下的行数
比如：如果BLOCKS_HIGH_WTR_MARK大于BLOCKS_ALLOCATED，则表示表空间被用足，需要扩容内存空间。
官方英文解释
DBA_HIGH_WATER_MARK_STATISTICS displays information about database high-watermark statistics.
| Column | Datatype | NULL | Description |
|---|---|---|---|
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Identifier of the database for which the high-watermark statistics are tracked |
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Name of the high-watermark statistic (see Table 5-1) |
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Database version in which the high watermarks were tracked |
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Highest value of the statistic seen at sampling time |
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Value of the statistic at the last sample time |
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Description of the high-watermark statistics (see Table 5-1) |
Table 5-1 DBA_HIGH_WATER_MARK_STATISTICS Statistics
| Name | Description |
|---|---|
|
ACTIVE_SESSIONS |
Maximum Number of Active Sessions seen in the system |
|
CPU_COUNT |
Maximum Number of CPUs |
|
DATAFILES |
Maximum Number of Datafiles |
|
DB_SIZE |
Maximum Size of the Database (Bytes) |
|
EXADATA_DISKS |
Number of physical disks |
|
INSTANCES |
Oracle Database instances |
|
PART_INDEXES |
Maximum Number of Partitions belonging to an User Index |
|
PART_TABLES |
Maximum Number of Partitions belonging to an User Table |
|
QUERY_LENGTH |
Maximum Query Length |
|
SEGMENT_SIZE |
Size of Largest Segment (Bytes) |
|
SESSIONS |
Maximum Number of Concurrent Sessions seen in the database |
|
SQL_NCHAR_COLUMNS |
Maximum Number of SQL NCHAR Columns |
|
TABLESPACES |
Maximum Number of Tablespaces |
|
USER_INDEXES |
Number of User Indexes |
|
USER_MV |
Maximum Number of Materialized Views (User) |
|
USER_TABLES |
Number of User Tables |
