oracle :性能优化的一个案例查找CPU 过高


一．通过top命令看CPU的利用率：

#top
以下是TOP的结果：
last pid: 11225; load averages: 7.95, 6.63, 6.25 17:19:35
273 processes: 259 sleeping, 3 running, 5 zombie, 3 stopped, 3 on cpu
CPU states: 10.0% idle, 75.0% user, 15.0% kernel, 0.0% iowait, 0.0% swap
Memory: 8192M real, 4839M free, 2147M swap in use, 12G swap free
PID USERNAME THR PRI NICE SIZE RES STATE TIME CPU COMMAND
10929 oracle 1 59 0 1048M 1022M cpu/6 2:52 21.59% oracle
11224 oracle 1 59 0 1047M 1018M run 0:03 4.22% oracle
8800 oracle 1 59 0 1048M 1022M run 1:39 3.99% oracle
4354 oracle 1 59 0 1049M 1023M cpu/4 0:28 3.46% oracle
3537 oracle 1 59 0 1048M 1022M sleep 1:01 1.93% oracle
29499 oracle 1 59 0 1048M 1022M sleep 30.0H 1.84% oracle
11185 oracle 1 59 0 1047M 1020M sleep 0:01 0.74% oracle
11225 wacos 1 44 0 2832K 1928K cpu/0 0:00 0.65% top
9326 oracle 1 59 0 1047M 1020M sleep 0:58 0.50% oracle
410 root 14 59 0 7048K 6896K run 76.3H 0.42% picld
21363 oracle 1 59 0 1047M 1019M sleep 574:35 0.36% oracle
10782 oracle 11 59 0 1052M 1024M sleep 749:05 0.28% oracle
13415 oracle 1 59 0 1047M 1019M sleep 6:07 0.27% oracle
5679 oracle 11 59 0 1052M 1026M sleep 79:23 0.19% oracle
5477 oracle 258 59 0 1056M 1021M sleep 57:32 0.14% oracle
二．通过分析找出了消耗CPU最高进程对应的SQL语句：
SQL>set line 240
SQL>set verify off
SQL>column sid format 999
SQL>column pid format 999
SQL>column S_# format 999
SQL>column username format A9 heading "ORA User"
SQL>column program format a29
SQL>column SQL format a60
SQL>COLUMN OSname format a9 Heading "OS User"
SQL>SELECT P.pid pid,S.sid sid,P.spid spid,S.username username,
S.osuser osname,P.serial# S_#,P.terminal,P.program program,
P.background,S.status,RTRIM(a.sql_text) SQL
FROM v$process P, v$session S,v$sqlarea A WHERE P.addr = s.paddr AND S.sql_address = a.address (+) AND P.spid LIKE '%&1%';
Enter value for 1:10929
最终找到的SQL语句如下：
SELECT NVL(SUM(RURALCHARGE),0.00) AS Fee FROM LOCALUSAGE WHERE ServiceID=219987 and starttime >= to_date('2003/12/30 13:24:20','YYYY/MM/DD HH24:MI:SS');

三．查询localusage表上的分区索引：
通过以下查询得到localusage表上的分区索引有两个：
SQL> select INDEX_NAME from user_part_indexes where TABLE_NAME='LOCALUSAGE';

INDEX_NAME
------------------------------
I_LOCALUSAGE_SID
UI_LOCALUSAGE_ST_SEQ

通过执行计划分析出这条语句使用的是UI_LOCALUSAGE_ST_SEQ索引，没有使用I_LOCALUSAGE_SID索引，我统计了一下时间，用UI_LOCALUSAGE_ST_SEQ这个索引的效率很差的，返回时间用了2分钟36秒，而使用I_LOCALUSAGE_SID这个索引的话，返回时间为1秒多。而ORACLE缺省使用的是UI_LOCALUSAGE_ST_SEQ索引，因此占用了大量的CPU资源，导致CPU利用率下降。

以下是用autotrace的分析过程：
SQL>connect wacos/oss
SQL>set autotrace on
SQL> set timing on
SQL> SELECT NVL(SUM(RURALCHARGE),0.00) AS Fee FROM LOCALUSAGE WHERE ServiceID=219987 and starttime >= to_date('2003/12/30 13:24:20','YYYY/MM/DD HH24:MI:SS');
FEE
----------
107.25

Elapsed: 00:02:36.19 （返回时间2分36秒）

Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=10 Card=1 Bytes=35)
1 0 SORT (AGGREGATE)
2 1 PARTITION RANGE (ALL)
3 2 TABLE ACCESS (BY LOCAL INDEX ROWID) OF 'LOCALUSAGE' (C
ost=10 Card=10035 Bytes=351225)

4 3 INDEX (RANGE SCAN) OF 'UI_LOCALUSAGE_ST_SEQ' (UNIQUE
) (Cost=2 Card=10035)

Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
11000821 consistent gets
349601 physical reads
0 redo size
292 bytes sent via SQL*Net to client
359 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
1 rows processed

用HINT强制ORACLE使用I_LOCALUSAGE_SID索引,然后查看执行计划:
SQL>connect wacos/oss
SQL>set autotrace on
SQL>set timing on
SQL> SELECT /*+ INDEX(LOCALUSAGE I_LOCALUSAGE_SID)*/ NVL(SUM(RURALCHARGE),0.00) AS Fee FROM LOCALUSAGE WHERE ServiceID=219987 and

starttime >= to_date('2003/12/30 13:24:20','YYYY/MM/DD HH24:MI:SS');

FEE
----------
107.25
Elapsed: 00:00:01.15 （返回时间1秒）
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=15 Card=1 Bytes=35)
1 0 SORT (AGGREGATE)
2 1 PARTITION RANGE (ALL)
3 2 TABLE ACCESS (BY LOCAL INDEX ROWID) OF 'LOCALUSAGE' (Cost=15 Card=10035 Bytes=351225)
4 3 INDEX (RANGE SCAN) OF 'I_LOCALUSAGE_SID' (NON-UNIQUE) (Cost=14 Card=10035)
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
307 consistent gets
232 physical reads
0 redo size
292 bytes sent via SQL*Net to client
359 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
建议研发人员调整该语句，使这条语句缺省使用I_LOCALUSAGE_SID索引，或在语句中使用HINT来强制使用I_LOCALUSAGE_SID索引。