Oracle教程 2023-04-08

Oracle 视图 V$EVENT_HISTOGRAM 官方解释，作用，如何使用详细说明

本站中文解释

Oracle视图V$EVENT_HISTOGRAM显示系统事件统计结果，保存着从数据库实例启动到结束的采样结果。V$EVENT_HISTOGRAM基本按照stats_begin和end_time排序，stats_begin为采样开始时间，而END_TIME是采样结束时间。

根据采样的历史事件统计数据，我们可分析SGA的事件统计信息，从而评估数据库的性能。通常我们可以查询一段时间内占用最多CPU资源的事件类型，以及系统因为这些事件类型而等待的时间等情况。

使用V$EVENT_HISTOGRAM视图，可以非常方便地查看最耗时的事件类型，以及等待时间。可以使用以下SQL语句来查询：

SELECT event_id, event_name, sample_time, wait_time FROM v$event_histogram WHERE wait_time > 0;

官方英文解释

V$EVENT_HISTOGRAM displays a histogram of the number of waits, the maximum wait, and total wait time on an event basis, in milliseconds. The histogram has buckets of time intervals from < 1 ms, < 2 ms, < 4 ms, < 8 ms, … < 2²¹ ms, < 2²² ms, and >= 2²² ms.

The histogram will not be filled unless the TIMED_STATISTICS initialization parameter is set to true.

Column	Datatype	Description
`EVENT#`	`NUMBER`	Event number
`EVENT`	`VARCHAR2(64)`	Name of the event
`WAIT_TIME_MILLI`	`NUMBER`	Amount of time the bucket represents (in milliseconds). If the duration = `num`, then this column represents waits of duration < `num` that are not included in any smaller bucket.
`WAIT_COUNT`	`NUMBER`	Number of waits of the duration belonging to the bucket of the histogram
`LAST_UPDATE_TIME`	`VARCHAR2(64)`	Indicates the last time the bucket was updated (the ending timestamp of the last wait falling into the bucket’s duration)
`CON_ID`	`NUMBER`	The ID of the container to which the data pertains. 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

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