Oracle 优化 - CPU 问题

作为 OLTP 应用，一般不太有 CPU 问题，比较少 - 毕竟大多数问题都是 IO 引起；但是偶尔也会有。
问题判断
- 很简单 - OS 出现 CPU 很高的问题，持续高于 90%
- 应用可能会表现慢
问题调查和解决
- 硬件
- 消耗 CPU 的 SQLs
- 限制消耗 CPU 的 SQLs
硬件
- 根据经验和具体情况增加新的 CPUs，曾经很难，在目前虚拟化普遍使用的情况下，不再是太大的困扰。
消耗 CPU 的 SQLs
- AWR report 里面的 SQL ordered by CPU Time 会明确的告诉原因。比如下面红色的 SQL ID 69vuwhdz0jw51消耗了 Oracle 57% 的 CPU.
- 这个 SQL 每次执行 0.22 秒 CPU, 实际耗时（Elapsed Time / Executions = 0.5 秒左右）；再结合具体的 SQL, 没有优化的余地，那么需要要么修改代码减少调用次数，要么修改代码简化 SQL

SQL ordered by CPU Time

- Resources reported for PL/SQL code includes the resources used by all SQL statements called by the code.
- % Total is the CPU Time divided into the Total CPU Time times 100
- Total CPU Time (s): 56,812
- Captured SQL account for 79.1% of Total
- Total CPU Time (s): 56,812
- Captured PL/SQL account for 0.9% of Total

CPU Time (s)	Elapsed Time (s)	Executions	CPU per Exec (s)	% Total	% Total DB Time	SQL Id	SQL Module
32,595	96,381	149,476	0.22	57.37	47.42	69vuwhdz0jw51	JDBC Thin Client
1,940	5,451	190	10.21	3.41	2.68	47y171y2nuvy9	JDBC Thin Client
1,232	3,816	5,717	0.22	2.17	1.88	3x365dut1trbz	JDBC Thin Client
1,013	3,147	4,722	0.21	1.78	1.55	8vmfr11dt6bb7	JDBC Thin Client
908	2,792	4,225	0.21	1.60	1.37	9kxdmwbytzsbs	JDBC Thin Client
848	2,139	451	1.88	1.49	1.05	9zv8ryyqzjudh	JDBC Thin Client
564	1,651	2,530	0.22	0.99	0.81	bdd9ay1mz8x22	JDBC Thin Client
558	1,637	2,532	0.22	0.98	0.81	1pfxcnwp9ydw9	JDBC Thin Client
556	1,633	2,532	0.22	0.98	0.80	dwysa8fbxz8du	JDBC Thin Client
500	1,496	2,288	0.22	0.88	0.74	57jgy744z6rq3	JDBC Thin Client

- 也可以使用下面的 SQLs 来更细的分析 TOP CPU SQLs.
按照 CPU 总耗时排序（执行次数 X 每次的 CPU 耗时）

select a.SQL_ID,c.username, CPU_TIME*0.000001 cpu_time_secs,
ELAPSED_TIME*0.000001 elapsed_time_secs,round(ELAPSED_TIME*0.000001/nvl(nullif(executions,0),1)) Elap_per_Exec,
executions,ROWS_PROCESSED,b.piece line#,b.sql_text
from v$sql a, v$sqltext b,dba_users c
where
a.address=b.address
and
(
ELAPSED_TIME*0.000001>10
or executions > 1000
)
and executions>0
and c.user_id=a.PARSING_USER_ID
order by CPU_TIME,a.HASH_VALUE, b.piece asc

按照 SQL 单次执行的CPU 耗时排序

select c.username,CPU_TIME*0.000001 cpu_time_secs,
       ELAPSED_TIME*0.000001 elapsed_time_secs,
       round(ELAPSED_TIME*0.000001/nvl(nullif(executions,0),1)) Elap_per_Exec,
       executions,LAST_LOAD_TIME,
       b.piece line#,
       b.sql_text sql_text
from v$sql a, v$sqltext b, dba_users c
where
a.address=b.address
and
(
ELAPSED_TIME*0.000001>10
or executions > 1000
)
and executions>0
and c.user_id=a.PARSING_USER_ID
order by Elap_per_Exec,ELAPSED_TIME,CPU_TIME,a.HASH_VALUE, b.piece asc;

资源限制 - 终止 CPU 耗时超过一定阀值的 SQL

Create resource limit to limit SQLs which run more than 5 minutes.
alter system set resource_limit =true scope=both; (Oracle restart required to take effect)
create profile cpu_limit_3_min limit cpu_per_call 30000; (time is in 100ths of a second)
alter user XXXX profile cpu_limit_5_min; (change the user to use the profile)

巴特西

Oracle 优化 - CPU 问题

SQL ordered by CPU Time

最新文章

热门文章