oracle数据库性能方面常用sql

oracle数据库性能方面常用sql

1.清除数据库缓存

alter system flush shared_pool;
alter system flush buffer_cache;
alter system flush global_context;

2.sql方面

1）.查看数据库每次执行耗时前10的sql

select 
	* 
from (
	select
		v.sql_text as "sql语句",
		v.elapsed_time as "sql执行耗时",
		v.cpu_time as "CPU耗时",
		v.disk_reads as "IO耗时",
		v.executions as "执行次数",
		round(v.elapsed_time/v.executions/1000000,2) as "每次执行时间/s"
		rank()over(order by v.elapsed_time/v.executions desc) elapsed_rank
		from
			v$sql v
		where
			v.parsing_schema_name not in ('SYS','SYSTEM')
			and v.command_type <>  47
			and (v.module is null or v.module not like 'DBMS%')
	) a
where
	elapsed_rank <= 10

3.表方面

1）查询表空间信息

select
	a.tablespace_name as "表空间名",
	total as "表空间大小",
	free as "表空间剩余大小",
	(total - free) as "表空间使用大小",
	total/(1024*1024*1024) as "表空间大小(G)",
	free/(1024*1024*1024) as "表空间剩余大小(G)",
	(total - free)/(1024*1024*1024) as "表空间使用大小(G)",
	round((total-free)/total,4) * 100 as "使用率%"
from
	(select tablespace_name,sum(bytes) free from dba_free_space group by tablespace_name) a
	(select tablespace_name,sum(bytes) total from dba_data_files group by tablespace_name) b
where
	a.tablespace_name = b.tablespace_name
order by
	"使用率%" desc;

2）查询表扩容

select 
	file_name,
	tablespace_name as "表空间名称",
	autoextensible as "是否允许扩容",
	maxbytes,
	increment_by as "每次扩容大小"
from
	dba_data_files
order by
	increment_by desc;

3）查询表的使用频率

select 
	ss.owner,
	ss.object_name as "表名",
	ss.object_type,
	sum(ss.values) as "次数"
from
	v$segment_statistics ss
where
	ss.object_type = 'TABLE'
group by
	ss.owner,
	ss.object_name,
	ss.object_type
order by
 	"次数" desc;

4）查询数据量大于一百万的表

select
	table_name as "表名",
	to_char(num_rows,'999,999,999,999') as num_rows as "数据量"
from
	all_tables
where
	num_rows >= 1000000
order by
	"数据量" desc;

4.其他

1）指定返回数据量

rownum < 10

如：

select
	*
from
	user u
where
	u.name = '张三'
	and rownum < 10;

2)使用指定索引

/+INDEX  (表名  索引名)/

如：

select /+INDEX  (u name_age)/
	*
from
	user u
where
	u.name = '张三';