Auto Sort Area Managementk
- Parameter for automatic sort area management:
- -PGA_AGGREGATE_TARGET(Ranges from 10MB to 4000GB)
- -WORKAREA_SIZE_POLICY （AUTO | MANUAL）(Oracle 推荐使用自动化管理)
- Replaces all *_AREA_SIZE parameters
SQL> show parameter PGA_AGGREGATE NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ pga_aggregate_target big integer 0
SQL> show parameter workarea_size_policy NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ workarea_size_policy string AUTO
正常情况下，oracle server 对workarea_size_policy参数的设置是AUTO的，同时还可以根据实际需要，将AUTO修改为MANUAL,以满足对某个特定用户的操作(比如说某个特定用户，需要对大概10GB的数据进行排序;那么就可以将参数值修改MANULA,专为此特定用户给予满足要求的尺寸设置).
Setting Initially
The value of the PAG_AGGREGATE_TARGET initializaiton parameter(for example 100000KB,2500MB,or 50GB)should be set based on the total amount of memory available for the Oracle instance.This value can then be turened and dynamically modified at the instance level.Example 7-2 illustrates a typical situation.
- Leave 20% of the available memory to other applications.
- Leave 80% of memory to the Oracle instance.
- For OLTP:
PGA_AGGREGATE_TARGET=(total_mem*80%)*20%
- For DSS:
PGS_AGGREGATE_TARGET=(total_mem*80*)*50%
Setting Initially Example
Assume that an Oracle instance is configured to run on a system with 4GB of physical memory.Part of that memory should be left for the operating system and other non-Oracle applciations running on the same hardwares system .You might decide to dedicate only 80%(3.2GB) of the available memory to the Oracle instance.
You must then divide the resulting memory between the SGA and the PGA.
- For OLTP systems,the PGA memory typically accounts for a small fraction of the total memory available(for example,20%),leaving 80% for the SGA.
- For DSS systems running large,memory-intensive queries,PGA memory can typically use up to 70% of that total(up to 2.2GB in this example).
Good initial values for the parameter PGA_AGGREGATE_TARGET might be:
- For OLTP:PGA_AGGREGATE_TARGET=(total_mem*80%)*20%
- For DSS:PGA_AGGREGATE_TARGET=(total_mem*80%)*50%
where total_mem is the total amount of physical memory available on the system.
通过上述公式可以，进行初始值的设定；但是仅仅是初始值，在以后的业务发展过程中，可能随着workload的加大，当初的初始值可能会修改，那是必然的.
PGA Management Resources
Statistics to manage the PAG_AGGREGATE_TARGET initialization parameter
- Views for monitoring the PGA work area include:
- -v$sql_workarea_histogram
- -v$pgastat
- -v$sql_workarea_active
- -v$sql_workarea
- -v$tempseg_usage
- Views to assist in sizing the PGA work area are:
- -v$pga_target_advice(advice->oracle server根据日常使用情况,计算出的推荐值;advice是个好东西)
- -v$pga_target_advice_histogram
要仔细分析上图中各个动态性能试图之间的逻辑关系（关联关系）.
V$PGASTAT重点掌握cache hit percentage参数以及其计算公式.
V$SQL_WORKAREA_ACTIVE里面记录着当前正在活动的
instance启动之后，凡是进行排序的操作，通过V$SQL_WORKAREA_HISTOGRAM都可历史的记录，多少工作区是工作在optimal状态？多少工作区是工作在one-pass状态？多少工作区是工作在multi-pass状态.通过这些数据，就可以判断出PGA的设置是大还是小
SQL> select * from v$pgastat; NAME VALUE UNIT -------------------------------------------------- ---------- ------------ aggregate PGA target parameter 1308622848 bytes aggregate PGA auto target 1056033792 bytes global memory bound 130856960 bytes total PGA inuse 135250944 bytes total PGA allocated 159670272 bytes maximum PGA allocated 248479744 bytes total freeable PGA memory 16252928 bytes process count 29 max processes count 39 PGA memory freed back to OS 2343960576 bytes total PGA used for auto workareas 0 bytes NAME VALUE UNIT -------------------------------------------------- ---------- ------------ maximum PGA used for auto workareas 29012992 bytes total PGA used for manual workareas 0 bytes maximum PGA used for manual workareas 541696 bytes over allocation count 0 bytes processed 6328429568 bytes extra bytes read/written 34598912 bytes cache hit percentage 99.45 percent recompute count (total) 114860 19 rows selected.
动态性能视图:v$pgastat参数含义解读:
over allocation count ---> 0此参数值为0(表示超过负荷的次数)，表示负荷正常.就是说DBA设置的PGA相关参数大小合适，没有超过负荷；假如在生产环境下，负荷过大,over allocation count这个参数的值，将会逐渐递增.此时就要考虑增大PGA参数值.
v$pgastat Statistics
