Oracle教程 2023-04-05

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

Oracle视图DBA_HIST_EVENT_HISTOGRAM用于查询V$ACTIVE_SESSION_HISTORY视图中每个会话在每个事件之间经历的每个时间间隔段的数量。它提供了大量关于运行会话花在特定活动上的时间数据，用于确定数据库中经常性慢查询等性能问题的时间和异常的可能性。

要使用DBA_HIST_EVENT_HISTOGRAM视图，必须首先启动数据库的统计信息收集器，如果没有，可能无法查看DBA_HIST_EVENT_HISTOGRAM视图的任何内容。首先运行以下查询，以确定回收统计信息的间隔和阈值设置：

SQL> SELECT snap_interval,
snap_level
FROM dba_hist_baseline
WHERE baseline_name = ‘DEFAULT_BASELINE’;

若参数snap_interval为0，表示统计信息收集未启动。可以使用如下命令启动统计信息收集器：

SQL > EXEC DBMS_WORKLOAD_REPOSITORY.MODIFY_SNAPSHOT_SETTINGS(’60’,’FORALL’,’DAILY’,’60’,’TYPICAL’,’DEFAULT_BASELINE’);

现在, 您可以使用DBA_HIST_EVENT_HISTOGRAM视图来查看系统活动事件的历史数据：

SQL>
SELECT *
FROM dba_hist_event_histogram
WHERE …
ORDER BY …;

DBA_HIST_EVENT_HISTOGRAM displays event histogram historical statistics information.

This view contains snapshots of V$EVENT_HISTOGRAM.

Column	Datatype	NULL	Description
`SNAP_ID`	`NUMBER`	`NOT NULL`	Unique snapshot ID
`DBID`	`NUMBER`	`NOT NULL`	Database ID for the snapshot
`INSTANCE_NUMBER`	`NUMBER`	`NOT NULL`	Instance number for the snapshot
`EVENT_ID`	`NUMBER`	`NOT NULL`	Identifier of the wait event
`EVENT_NAME`	`VARCHAR2(64)`	`NOT NULL`	Name of the wait event
`WAIT_CLASS_ID`	`NUMBER`		Identifier of the class of the wait event
`WAIT_CLASS`	`VARCHAR2(64)`		Name of the class of the wait event
`WAIT_TIME_MILLI`	`NUMBER`	`NOT NULL`	Wait time (in milliseconds)
`WAIT_COUNT`	`NUMBER`		Wait count
`CON_DBID`	`NUMBER`		The database ID of the PDB for the sampled session
`CON_ID`	`NUMBER`		The ID of the container that `CON_DBID` identifies. Possible values include: `0`: This value is used for rows containing data that pertain to the entire CDB. This value is also used for rows in non-CDBs. `1`: This value is used for rows containing data that pertain to only the root n: Where n is the applicable container ID for the rows containing data