用Oracle实现ASH的数据透视图

11g里面有个很有用的新特性,对数据透视图的支持。

简单而言,它可以实现宽表和窄表之间的转化。举一个例子,有一张表记录了全校所有班级所有学生的成绩(A,B,C,D,E),现在想统计每个班级里每个分数级别对应的学生人数。当然,一个SQL就可以实现:

SELECT class, score, count(*) FROM score_table
GROUP BY class, score;

结果的格式如下:

班级      分数 人数
一年一班     A  10
一年一班     B  16
一年一班     C  16
一年一班     D  16
一年一班     E  16
一年二班     A  15
一年二班     B  14
一年二班     C  15
一年二班     D  14
一年二班     E  15

不过,很多人更想要下面的格式

班级        A    B   C   D   E
一年一班   10   16  16  16  16
一年二班   15   14  15  14  15

第二种格式显然简单明了多了。

用Oracle的新语法,可以实现如下

SELECT *
FROM
(
SELECT class,score,count(*) cnt 
FROM score_table 
GROUP BY class,score
)
pivot
(
sum(cnt) FOR score IN ('A','B','C','D','E')
)
;

一个更实用的场合是对ASH(active session history)数据的处理上。

一般而言,我们需要一段时间内Top 10的wait event,并掌握其在每个时间片(例如10 seconds)里的分布。这些信息可以通过下面的SQL进行获取:

SELECT
    to_char(to_date(trunc(to_char(sample_time,'SSSSS')/10)*10,'SSSSS'),'hh24:mi:ss') start_time
  , decode(ash.session_state,'ON CPU','ON CPU',ash.event)     event
  , count(1)/10 total
FROM
   v$active_session_history ash
WHERE
          sample_time > sysdate-1/24
GROUP BY  trunc(to_char(sample_time,'SSSSS')/10)
       ,  decode(ash.session_state,'ON CPU','ON CPU',ash.event)
;

同样的,我们更习惯将这个结果进行倒置。这同样可以通过pivot来实现:

SELECT * FROM                   
(SELECT
    to_char(to_date(trunc(to_char(sample_time,'SSSSS')/10)*10,'SSSSS'),'hh24:mi:ss') start_time
  , decode(ash.session_state,'ON CPU','ON CPU',ash.event)     event
  , count(1)/10 total
FROM
   v$active_session_history ash
WHERE
          sample_time >  sysdate-1/24
GROUP BY  trunc(to_char(sample_time,'SSSSS')/10)
       ,  decode(ash.session_state,'ON CPU','ON CPU',ash.event)
) ash       
pivot (sum(total) FOR event IN ('ON CPU' AS TOP1,'PX Deq: Slave Session Stats' AS TOP2))
ORDER BY 1;

下面是一个ASH的例子,系统的工作状态已经一目了然了!

TOP   EVENT
----- ----------------------------------------------------------------
TOP1  cell smart table scan
TOP2  ASM file metadata operation
TOP3  control file sequential read
TOP4  ON CPU
TOP5  enq: XL - fault extent map
TOP6  DFS lock handle
TOP7  cell single block physical read
TOP8  reliable message
TOP9  read by other session
TOP10 latch: shared pool

TIME      TOP1  TOP2  TOP3  TOP4  TOP5  TOP6  TOP7  TOP8  TOP9 TOP10
-------- ----- ----- ----- ----- ----- ----- ----- ----- ----- -----
00:30:50                       1
00:31:30
00:31:40
00:31:50
00:32:10
00:32:30
00:32:50                       1
00:34:10
00:34:30                       1
00:34:40
00:35:10                       1
00:35:40                       1
00:37:50    16    34     5     9     2           1    14     3     9
00:38:00   296    95     7     9     3           6     1     6
00:38:10   478   133    15     4    17           7           1
00:38:20   543    71    21     6     8           7           5
00:38:30   531    81    13     2    14           9     1     2
00:38:40   600    30    17     4     2     1     2
00:38:50   592    36    16     4     5    10     1
00:39:00   609    20    12     6          10           4
00:39:10   620    14    13     4     2    10
00:39:20   628     5    10     4          10     1
00:39:30   248     7     4                 4           4
posted on 2009-09-24 12:01  一江水  阅读(2533)  评论(0编辑  收藏  举报