等待级别和等待事件相关动态性能视图

--等待级别和等待事件相关动态性能视图

--通过查询v$event_name可以得知当前版本有哪些等待事件及其等待级别。
SYS@PROD1> select wait_class, count(*) from v$event_name group by rollup(wait_class) order by wait_class;

WAIT_CLASS							   COUNT(*)
---------------------------------------------------------------- ----------
Administrative								 55
Application								 17
Cluster 								 50
Commit									  2
Concurrency								 33
Configuration								 24
Idle									 95
Network 								 35
Other									745
Queueing								  9
Scheduler								  8
System I/O								 31
User I/O								 48
1152

14 rows selected.

SYS@PROD1> select name from v$event_name where wait_class='Application' and rownum<15;

NAME
----------------------------------------------------------------
enq: PW - flush prewarm buffers
enq: RO - contention
enq: RO - fast object reuse
enq: KO - fast object checkpoint
enq: TM - contention
enq: TX - row lock contention
Wait for Table Lock
enq: RC - Result Cache: Contention
Streams capture: filter callback waiting for ruleset
Streams: apply reader waiting for DDL to apply
SQL*Net break/reset to client
SQL*Net break/reset to dblink
External Procedure initial connection
External Procedure call

14 rows selected.

--对于会话级别的统计信息，可以通过v$session_wait_class。
SYS@PROD1> select sid from v$mystat where rownum=1;

SID
----------
1

SYS@PROD1> SELECT wait_class,
2  	    round(time_waited, 3) AS time_waited,
3  	    round(1E2 * ratio_to_report(time_waited) OVER (), 1) AS "%"
4  FROM (
5    SELECT sid, wait_class, time_waited / 1E2 AS time_waited
6    FROM v$session_wait_class
7    WHERE total_waits > 0
8    UNION ALL
9    SELECT sid, 'CPU', value / 1E6
10    FROM v$sess_time_model
11    WHERE stat_name = 'DB CPU'
12  )
13  WHERE sid = 1
14  ORDER BY 2 DESC;

WAIT_CLASS							 TIME_WAITED	      %
---------------------------------------------------------------- ----------- ----------
Idle								    25202.32	   99.9
User I/O								11.6	      0
CPU								       3.014	      0
Other									2.14	      0
System I/O								1.08	      0
Commit									 .12	      0
Configuration								 .03	      0
Concurrency								 .02	      0
Network 								   0	      0
Application								   0	      0

10 rows selected.

--对于一些等待事件，可以查询得到平均延迟的信息。
SYS@PROD1> select time_waited_micro/total_waits/1E3 as avg_wait_ms from v$system_event where event = 'db file sequential read';

AVG_WAIT_MS
-----------
10.958592

--Oracle为每个等待事件提供直方图，v$event_histogram。
SYS@PROD1> SELECT wait_time_milli, wait_count, 100*ratio_to_report(wait_count) OVER() AS "%"
2  FROM v$event_histogram
3  WHERE event = 'db file sequential read';

WAIT_TIME_MILLI WAIT_COUNT	    %
--------------- ---------- ----------
1       4177  54.050207
2        145   1.876294
4        169   2.186853
8        559 7.23343685
16       1294 16.7443064
32        775 10.0284679
64        377 4.87836439
128        171 2.21273292
256 	55 .711697723
512 	 5 .064699793
1024 	 1 .012939959

11 rows selected.