oracle效能調優常用語句
--識別'低效執行'的sql語句：
select executions , disk_reads, buffer_gets,
round((buffer_gets-disk_reads)/buffer_gets,2) hit_radio,
round(disk_reads/executions,2) reads_per_run,
sql_text
from v$sqlarea
where executions>0
and buffer_gets > 0
and (buffer_gets-disk_reads)/buffer_gets < 0.8
order by 4 desc;
----檢視連線數
select count(*) from v$session;
----檢視併發連線數
select count(*) from v$session where status='active';
----檢視最大連線
show parameter processes;
--檢視表空間情況
select sum(bytes)/(1024*1024) as free_space,tablespace_name
from dba_free_space
group by tablespace_name;
--檢視回滾段名稱及大小
select segment_name, tablespace_name, r.status,
(initial_extent/1024) initialextent,(next_extent/1024) nextextent,
max_extents, v.curext curextent
from dba_rollback_segs r, v$rollstat v
where r.segment_id = v.usn(+)
order by segment_name ;
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