oracle9i或10g中PGA的管理（转）

 

WORKAREA_SIZE_POLICY指的就是PGA的管理，PGA的管理分手工和自动（PGA里非UGA的部分，比如sorting，hashing）,以下参数在手工管理时用到SORT_AREA_SIZE,SORT_AREA_RETAINED_SIZE,sort结束后保留的大小,比如 SORT_AREA_SIZE是1M, SORT_AREA_RETAINED_SIZE是512K,则一个大的SORT可能用完1M,SORT 完后超过512K的会交换到TEMP SEGMENT里.

HASH_AREA_SIZE server process用来在内存里存hash table的大小.

大致来看,如果workarea_size_policy=manual那么pga_aggregate_target将会不被使用,而是使用响应的sort_area_size,hash_area_size等参数.;如果workarea_size_policy=auto的话那么就会使用pga_aggregate_target而不使用其他的sort_area_size,hash_area_size等参数.

if ( 数据库版本 >= 10gR1 )

then

if (workarea_size_policy=auto)

then

sort area size 无效

else

sort area size 有效

end if

else -- 数据库版本 < 10gr1

if ( shared server 连接方式 )

then

sort area size 有效

else -- dedicated server连接方式

if (workarea_size_policy=auto)

then

sort area size 无效

else

sort area size有效

end if

end if

end if

• 用sort_area_size 512K,1M,1G来看手工与自动管理时的异同，以下是自动管理

SQL> create table wwm as select * from all_objects;

SQL> alter session set sort_area_size=524288;

session xxx memory表示现在这个时刻用了多少，session xxx memory max 表示最高峰时用了多少

SQL> set autotrace traceonly statistics;

SQL> select * from wwm order by 1,2,3,4

---------------------------------------------------------

0 recursive calls

0 db block gets

420 consistent gets

0 physical reads

0 redo size

2178018 bytes sent via SQL*Net to client

22768 bytes received via SQL*Net from client

2038 SQL*Net roundtrips to/from client

1 sorts (memory)

0 sorts (disk)

30547 rows processed

SQL> alter session set sort_area_size=1048576; 同上

SQL> alter session set sort_area_size=1048576000; 同上

自动管理时sort_area_size不起作用.

• 改成手工管理后

SQL> alter session set workarea_size_policy=manual;

SQL> alter session set sort_area_size = 65536; --64K

SQL> set autotrace traceonly statistics;

SQL> select * from wwm order by 1,2,3,4

----------------------------------------------------------

0 recursive calls

22 db block gets

420 consistent gets

513 physical reads

0 redo size

2178018 bytes sent via SQL*Net to client

22768 bytes received via SQL*Net from client

2038 SQL*Net roundtrips to/from client

0 sorts (memory)

1 sorts (disk)

30547 rows processed

============退出，重进

SQL> alter session set sort_area_size=1048576;

SQL> set autotrace traceonly statistics;

SQL> select * from wwm order by 1,2,3,4;

----------------------------------------------------------

0 recursive calls

4 db block gets

420 consistent gets

424 physical reads

0 redo size

2178018 bytes sent via SQL*Net to client

22768 bytes received via SQL*Net from client

2038 SQL*Net roundtrips to/from client

0 sorts (memory)

1 sorts (disk)

30547 rows processed

还有排序操作在DISK上

SQL> set autotrace off

==============退出，重进

SQL> alter session set sort_area_size=1048576000;

SQL> set autotrace traceonly statistics;

SQL> select * from wwm order by 1,2,3,4;

----------------------------------------------------------

0 recursive calls

0 db block gets

420 consistent gets

0 physical reads

0 redo size

2178018 bytes sent via SQL*Net to client

22768 bytes received via SQL*Net from client

2038 SQL*Net roundtrips to/from client

1 sorts (memory)

0 sorts (disk)

30547 rows processed

以上分别用64K,1M,1G来测试,分配1G并不代表就要切实分配1G的MEM出去。而是说你有权利用到1G,相反,设置64K并不代表你的session只能用64k,一个SQL可能有多个SORT,指的是每个SORT 的限额.