今天是2013-07-11日，首先我非常感谢我的哥们也是我的网友杨工，非常感谢他能在大数据库内帮我执行一下我所需要的信息。就是他说的网络真是一个互助友爱的平台。

前面，我学习 pga内存的结构concept以及常用的动态查看pga的分配使用情况。现在我在学习一下怎么启动pga管理。
如果启动一个自动管理的pga，需要配置二个参数，一个是pga_aggregate_target，一个是workarea_size_policy，这些参数在前面我学习了，但是如何设置pga_aggregate_target这个参数在刚刚创建新的库的时候是可以通过前面oracle建议的步骤进行设定的，
但是运行一段时间后我们还是需要重新设置该参数：
1）pga advice view；
在查看该相关视图需要确保statistics_level运行在typical或是all状态，不然就没法查看建议值了。

Setting the STATISTICS_LEVEL parameter toBASIC disables the collection of many of the important statistics required by Oracle Database features and functionality, including:

• Automatic Workload Repository (AWR) Snapshots

• Automatic Database Diagnostic Monitor (ADDM)

• All server-generated alerts

• Automatic SGA Memory Management

• Automatic optimizer statistics collection

• Object level statistics

• End to End Application Tracing (V$CLIENT_STATS)

• Database time distribution statistics (V$SESS_TIME_MODEL andV$SYS_TIME_MODEL)

• Service level statistics

• Buffer cache advisory

• MTTR advisory

• Shared pool sizing advisory

• Segment level statistics

• PGA Target advisory

• Timed statistics

• Monitoring of statistics
  eg：
  SYS@orcl#SHOW PARAMETER STATISTICS_LEVEL

NAME                                 TYPE                   VALUE
------------------------------------ ---------------------- ------------------------------
statistics_level                     string                 TYPICAL
SYS@orcl#R
  1* select PGA_TARGET_FOR_ESTIMATe/1024/1024 PGA_TARGET_FOR_ESTe,PGA_TARGET_FACTOR,ADVICE_STATUS,BYTES_PROCESSED/1024/1024 BYTES_PROCESSED,ESTD_TIME,ESTD_EXTRA_BYTES_RW/1024/1024 ESTD_EXTRA_BYTES_RW,ESTD_PGA_CACHE_HIT_PERCENTAGE,ESTD_OVERALLOC_COUNT from v$pga_target_advice

PGA_TARGET_FOR_ESTE PGA_TARGET_FACTOR ADVICE BYTES_PROCESSED  ESTD_TIME ESTD_EXTRA_BYTES_RW ESTD_PGA_CACHE_HIT_PERCENTAGE ESTD_OVERALLOC_COUNT
------------------- ----------------- ------ --------------- ---------- ------------------- ----------------------------- --------------------
                 32              .125 ON          1018.20703      22139          289.753906                            78                   41
                 64               .25 ON          1018.20703      22139          289.753906                            78                   41
                128                .5 ON          1018.20703      17235                   0                           100                    0
                192               .75 ON          1018.20703      17235                   0                           100                    0
                256                 1 ON          1018.20703      17235                   0                           100                    0
         307.199219               1.2 ON          1018.20703      17235                   0                           100                    0
         358.399414               1.4 ON          1018.20703      17235                   0                           100                    0
         409.599609               1.6 ON          1018.20703      17235                   0                           100                    0
         460.799805               1.8 ON          1018.20703      17235                   0                           100                    0
                512                 2 ON          1018.20703      17235                   0                           100                    0
                768                 3 ON          1018.20703      17235                   0                           100                    0

PGA_TARGET_FOR_ESTE PGA_TARGET_FACTOR ADVICE BYTES_PROCESSED  ESTD_TIME ESTD_EXTRA_BYTES_RW ESTD_PGA_CACHE_HIT_PERCENTAGE ESTD_OVERALLOC_COUNT
------------------- ----------------- ------ --------------- ---------- ------------------- ----------------------------- --------------------
               1024                 4 ON          1018.20703      17235                   0                           100                    0
               1536                 6 ON          1018.20703      17235                   0                           100                    0
               2048                 8 ON          1018.20703      17235                   0                           100                    0

已选择14行。
可以看到我们应该设置pga_aggregate_target大小为128M。
如果我把statistics_level参数设置为basic,那么oracle就会取消相关的功能。
另外还有v$pga_target_advice_histogram;这个视图。