相克军_Oracle体系_随堂笔记007-PGA

实际工作中，Oracle中有两个很重要：Server Process 和 PGA。

 

PGA内存作用和构成

 

1、PGA作用

2、PGA构成

1）private SQL area

 

2）Session Memory

 

（hold a session’s variables (logon information) and other information related to the session.）

 

3）SQL Work Areas

3、PGA管理方式

4、Dedicated Server、Shared Server

    目前大都是用Dedicated Server.

    如果是大型电商网站，访问很多，单个负载很小的话，就用Shared Server。

5、重要参数

PGA_AGGREGATE_TARGET

在OLTP系统中，典型PGA内存设置应该是总内存的较小部分（例如20％），剩下80％分配给SGA。 
OLTP：PGA_AGGREGATE_TARGET = (total_mem * 80%) * 20% 
在DSS系统中，由于会运行一些很大的查询，典型的PGA内存最多分配70％的内存。
DSS：PGA_AGGREGATE_TARGET = (total_mem * 80%) * 50% 
SQL> alter system set workarea_size_policy=auto scope=both;
SQL> alter system set pga_aggregate_target=512m scope=both;

 

WORKAREA_SIZE_POLICY

sort_area_size
sort_area_retained_size
hash_area_size
hash_join_enable
bitmap_merge_area_size
create_bitmap_area_size
open_cursors
_pga_max_size

select ksppinm "Name", ksppstvl/1024/1024 ||'M' "Value", ksppdesc "Desc" 
from x$ksppi x, x$ksppcv y 
where x.indx = y.indx and ksppinm ='_pga_max_size';

 

6、重要视图

V$PGASTAT

SELECT * FROM V$PGASTAT; 

 

V$PGA_TARGET_ADVICE

Select pga_target_for_estimate/1024/1024 ||'M' "Estimate PGA Target"
       ,estd_pga_cache_hit_percentage "Cache Hit(%)"
       ,estd_extra_bytes_rw/1024/1024 ||'M' "Extra Read/Write"
       ,estd_overalloc_count "Over alloc count"
From v$pga_target_advice

select (p.PGA_TARGET_FOR_ESTIMATE)/1024/1024,p.ESTD_PGA_CACHE_HIT_PERCENTAGE
from v$pga_target_advice p
where p.ESTD_PGA_CACHE_HIT_PERCENTAGE>95;

SELECT round(PGA_TARGET_FOR_ESTIMATE/1024/1024) target_mb, 
   ESTD_PGA_CACHE_HIT_PERCENTAGE cache_hit_perc, 
   ESTD_OVERALLOC_COUNT
   FROM v$pga_target_advice;

 

V$SYSSTAT 、V$SESSTAT 

select * from V$SYSSTAT
where name like '%sort%'; 

select name,value from v$statname a,v$mystat b where a.statistic#=b.statistic# and a.name like '%pga%';

 

V$SQL_WORKAREA

V$SQL_WORKAREA_ACTIVE

V$PROCESS

select spid,program,pga_max_mem,pga_alloc_mem,pga_used_mem,pga_freeable_mem
from v$process
where spid in (select spid from v$process where addr in 
(select paddr from v$session where sid in (select distinct sid from v$mystat)));

select spid,program,pga_max_mem,pga_alloc_mem,pga_used_mem,pga_freeable_mem
from v$process where PROGRAM like '%jiagulun%'

 

--查看PGA各个区域使用情况

select p.PROGRAM,p.SPID,pm.CATEGORY,pm.ALLOCATED,pm.USED,pm.MAX_ALLOCATED
from v$process p,v$process_memory pm
where p.PID=pm.PID
and p.SPID in (select spid from v$process where addr in
(select paddr from v$session where sid in
(select distinct sid from v$mystat )
));