statspack采样时，BUFFER命中率为什么会这么低？？
仔细看下面这行，在凌晨时很少人进行操作，但BUFFER命中率却非常低，为什么，如何改进？？
03:57:18
67
SQL> select
2substr(to_char(snap_time,'yyyy-mm-dd hh24:mi:ss'),12),
3round(100*(((a.value-e.value)+(b.value-f.value))-(c.value-g.value))/
4((a.value-e.value)+(b.value-f.value))) "BUFFER HIT PARIO"
5from
6perfstat.stats$sysstat a,
7perfstat.stats$sysstat b,
8perfstat.stats$sysstat c,
9perfstat.stats$sysstat d,
10perfstat.stats$sysstat e,
11perfstat.stats$sysstat f,
12perfstat.stats$sysstat g,
13perfstat.stats$snapshot sn
14where
15a.snap_id=sn.snap_id
16and b.snap_id=sn.snap_id
17and c.snap_id=sn.snap_id
18and d.snap_id=sn.snap_id
19and e.snap_id=sn.snap_id-1
20and f.snap_id=sn.snap_id-1
21and g.snap_id=sn.snap_id-1
22and a.statistic#=39
23and e.statistic#=39
24and b.statistic#=38
25and f.statistic#=38
26and c.statistic#=40
27and g.statistic#=40
28and d.statistic#=41
29/
SUBSTR(TO_CHAR(S BUFFER HIT PARIO
---------------- ----------------
12:50:49
100
13:51:15
99
15:52:07
98
16:52:33
97
17:52:59
99
18:53:25
100
19:53:50
99
20:54:16
99
21:54:42
99
22:55:08
100
23:55:34
99
SUBSTR(TO_CHAR(S BUFFER HIT PARIO
---------------- ----------------
00:56:01
98
01:56:27
99
02:56:53
97
03:57:18
67
04:57:45
94
05:58:11
99
06:58:37
99
07:59:02
100
08:59:28
99
10:00:12
99
11:00:37
100
SUBSTR(TO_CHAR(S BUFFER HIT PARIO
---------------- ----------------
12:01:03
99
13:01:29
99
14:01:54
99
15:02:20
97
16:02:46
99
17:03:13
97
18:03:38
100
19:04:04
100
20:04:30
100
21:04:56
99
22:05:21
98
SUBSTR(TO_CHAR(S BUFFER HIT PARIO
---------------- ----------------
23:05:47
100
00:06:14
98
01:06:41
96
02:07:07
99
03:07:34
99
04:07:59
100
05:08:25
97
06:08:51
100
07:09:17
99
08:09:43
99
09:10:09
98
SUBSTR(TO_CHAR(S BUFFER HIT PARIO
---------------- ----------------
10:10:35
98
11:11:01
98
12:11:27
99
13:11:53
100
14:12:19
100
15:12:46
97
16:13:12
96
17:13:38
99
18:14:04
99
19:14:30
99
20:14:56
99
SUBSTR(TO_CHAR(S BUFFER HIT PARIO
---------------- ----------------
21:15:22
99
22:15:48
99
23:16:14
94
00:16:41
100
01:17:06
97
02:17:32
100
03:17:58
100
04:18:25
99
05:18:51
97
06:19:16
90
07:19:42
95
SUBSTR(TO_CHAR(S BUFFER HIT PARIO
---------------- ----------------
08:20:09
100
已选择67行。
SQL> |
