Oracle 视图 DBA_HIGH_WATER_MARK_STATISTICS 官方解释，作用，如何使用详细说明

网络编程 Oracle 视图 DBA_HIGH_WATER_MARK_STATISTICS 官方解释，作用，如何使用详细说明 10-15

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
`DBID`	`NUMBER`	`NOT NULL`	Identifier of the database for which the high-watermark statistics are tracked
`NAME`	`VARCHAR2(64)`	`NOT NULL`	Name of the high-watermark statistic (see Table 5-1)
`VERSION`	`VARCHAR2(17)`	`NOT NULL`	Database version in which the high watermarks were tracked
`HIGHWATER`	`NUMBER`		Highest value of the statistic seen at sampling time
`LAST_VALUE`	`NUMBER`		Value of the statistic at the last sample time
`DESCRIPTION`	`VARCHAR2(128)`		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

编辑：广州明生医药有限公司

标签：索引,内存空间,水位,分配,它是