性能诊断与调优之V$--V$SESSION_WAIT_HISTORY

最新推荐文章于 2025-08-31 09:52:50 发布

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最新推荐文章于 2025-08-31 09:52:50 发布 · 4.8k 阅读

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#session #events #oracle #sql #database #performance

Oracle的V$SESSION_WAIT_HISTORY视图提供了每个连接会话最近10个等待事件的历史信息，用于性能诊断。当会话触发新事件时，最旧的事件会被移除，最新的事件显示为SEQ# 1。尽管10个槽位可能不足以应对活跃会话，但这是提供在线历史数据的一个积极步骤。V$ACTIVE_SESSION_HISTORY在Oracle 10g中提供了更丰富的历史性能数据，基于1秒采样间隔，但在V$SESSION_WAIT_HISTORY中只显示最近10次等待。

V$SESSION_WAIT_HISTORY View

Historical information has been lacking from the Oracle wait events views. Low-level historical data simply doesn’t exist, and DBAs have to rely on high-level data from V$SESSION_EVENT, V$SYSTEM_EVENT

and the Statspack utility for performance diagnosis. This view retains the 10 most recent wait events for each connected session. This is not a complete history, but it is a step in the right direction.

V$SESSION_WAIT_HISTORY从10g开始为每个session保留了等待事件的历史信息，其对应的字段如下:

SQL>   desc V$SESSION_WAIT_HISTORY;
Name       Type         Nullable Default Comments 
---------- ------------ -------- ------- -------- 
SID        NUMBER       Y                         
SEQ#       NUMBER       Y                         
EVENT#     NUMBER       Y                         
EVENT      VARCHAR2(64) Y