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翻译 Oracle 8i interal Service (2.2.3 Session Waits)

原创 Linux操作系统 作者:wwllzpz 时间:2019-05-14 10:57:06 0 删除 编辑

V$SESSION_EVENT shows the wait statistics for each live session. Although

waits affect processes rather than sessions, they are recorded against sessions

because sessions can migrate between processes (as in Multi-Threaded Server

configurations). The cumulative session wait statistics have two main uses.

V$session_event为每个存在的session显示等待统计量。尽管进程比会话更受等待的影响,他们也被记录。因为会话能在进程直接迁移,累积的会话等待统计量有两种主要的用途。

First, if a particular user reports an episode of poor performance, then the wait

statistics for that session can be examined to diagnose that user's problem. The

APT script called session_times.sql (see Example 2.2) shows the waiting time

accumulated by the session for each type of event waited for, together with the

amount of CPU time consumed by that session. This makes it easy to see whether

the session has been working or waiting, and if it has been waiting, what it has

been waiting for.

第一,如果某个用户反映性能差,那么他的sessionwait statistics能用来诊断这个用户的问题。Session_times.sql显示这个session各种等待的累积等待时间,和消耗的CPU时间。这样很容易看出这个session是在工作还是在等待,如果在等待,在等待什么。

Example 2.2. Sample Output from session_times.sql

SQL> @session_times

Enter SID: 29

EVENT

TIME_WAITED

---------------------------------------------------------------- ------

-----

SQL*Net message from client

2954196

CPU used by this session

1657275

db file sequential read

246759

write complete waits

139698

buffer busy waits

61832

log file sync

32601

enqueue

9576

log file switch completion

3530

SQL*Net message to client

2214

db file scattered read

1879

SQL*Net more data to client

952

SQL*Net more data from client

908

latch free

840

free buffer waits

100

buffer deadlock

57

row cache lock

1

SQL*Net break/reset to client

0

Second, if there has been extensive waiting for a particular type of resource, then

the session wait statistics can be used to determine which of the sessions that are

still connected have contributed to or been affected by the problem. The APT

script for this job is called resource_waiters.sql . It shows the breakdown by

session of the waiting time for the resource type in question. The total waiting

time for sessions that are no longer active is also shown. For example, if there

have been a large number of buffer busy waits, then looking at the session wait

statistics may reveal whether the problem has been widespread, or confined to

just a few sessions.

第二,如果一直特定的资源等待广泛,那么the session wait statistics能用来判断主要是哪个session造成的。Resource_waiters.sql可以完成这个工作。它显示等待这个资源类型的session的问题。非活动sessionthe total waiting time 也显示。举例来说,一个很大的buffer busy waits ,那么sessionwait sttistice 可以说明这个问题是普遍存在还是个别现象。

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