[bbk2194] 第35集 - Chapter 09-Optimizing Sore Perations(04)

OEM

PGA Target Advice Histograms

V$PGA_TARGET_ADVICE_HISTOGRAM predicts how histograms shown in V$SQL_WORKAREA_HISTOGRAM evolve.

STATISTICS_LEVEL must be set to at least TYPICAL.

Auto PGA and OEM

Overview

The automatic sort area management feature is :

Easier to set up and size than the *_AREA_SIZEP parameters

Easier to monitor using the advisory view

通常情况下，当多用户的时候，Oracle强烈推荐使用auto方式管理PGA；但是对于少量用户或者跑一些批量程序的时候可以设置成manual模式（一般仅限于SESSION级别:例子如下）

SQL>ALTER SESSION SET WORKAREA_SIZE_POLICY=MANUAL;
SQL>ALTER SESSION SET SORT_AREA_SIZE=your size;

The Sorting Process

If sort space requirement is greater than SORT_AREA_SIZE:

Sort Area and Prameters

The sort space is in:

The PGA for a dedicated server connection



The shared pool for Oracle Shared Server connection



如果oracle database server是dedicated server 模式，sort area是存放在PGA里面的.

如果oracle database server是shared server模式，sort area是存放在SGA里面的.

控制sort area尺寸大小的两个参数1->sort_area_size;2->sort_area_reatined_size;

Tuning Sorts

Use automatic sort area management.

Avoid sort operations whenever possible.

Reduce swapping and paging by making sure that sorting is done in memory when possible.

Reduce space allocation calls by allocating temporary space appropriately.

Sorting and Temp Space

Create a temporary tablespace by using:(临时表空间与普通表空间的创建还是有一些细微的差别)

CREATE TEMPORARY TABLESPACE TEMP TEMPFILE '$HOME/ORADATA/u06/temp01.dbf' size 200M;

普通表空间中，通常情况下包含多个segment.但是临时表空间，只包含一个segment.多个用户使用temporary tablespace的话，就是使用不同的extent.