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分类： Oracle
2007-01-04 18:01:48
070104-1.When a SQL statement is submitted to Oracle for execution, Oracle automatically
performs the following memory allocation steps:
1. Oracle checks the shared pool to see if a shared SQL area already exists for an
identical statement. If so, that shared SQL area is used for the execution of the
subsequent new instances of the statement. Alternatively, if there is no shared
SQL area for a statement, Oracle allocates a new shared SQL area in the shared
pool. In either case, the user’s private SQL area is associated with the shared
SQL area that contains the statement.
2. Oracle allocates a private SQL area on behalf of the session. The location of the
private SQL area depends on the type of connection established for the session.
（Oracle首先检查共享池是否存在相同的语句。如果有，则shared SQL area为后来的语句所使用。反之，如果共享池中没有这个语句，Oracle则在shared pool为该语句分配一个新的shared SQL area。无论那种情况，都为shared SQL area分配私有的private SQL area）
-2.The location of a private SQL area depends on the type of connection established for
a session. If a session is connected through a dedicated server, private SQL areas are
located in the server process’s PGA. However, if a session is connected through a
shared server, part of the private SQL area is kept in the SGA.
（private SQL area的存储区域依赖于会话连接的方式。如果会话通过专有服务期连接，则它被放在the server process’s PGA。如果是共享服务器的话保存在SGA）
-3.The following three columns in the V$PROCESS view report the PGA memory
allocated and used by an Oracle process:
PGA_USED_MEM
PGA_ALLOCATED_MEM
PGA_MAX_MEM
（v$process视图的上列三个列显示了PGA内存的配置和使用情况）
-4.Connections and Sessions
Connection and session are closely related to user process but are very different in
meaning.
A connection is a communication pathway between a user process and an Oracle
instance. A communication pathway is established using available interprocess
communication mechanisms (on a computer that runs both the user process and
Oracle) or network software (when different computers run the database
application and Oracle, and communicate through a network).
A session is a specific connection of a user to an Oracle instance through a user
process. For example, when a user starts SQL*Plus, the user must provide a valid
username and password, and then a session is established for that user. A session
lasts from the time the user connects until the time the user disconnects or exits the
database application.
（会话和连接对一个用户进程来说是不可分的，但是却有着不同的意思。
一个连接是用户进程与ORACLE例程间的一个通信的路径。通讯路径的建立是通过可用的进程间的通讯机制。
会话是用户通过用户的进程连接到oracle例程的一个明确的连接。一个会话持续到用户开始连接到用户断开连接或退出数据库应用。）
Oracle Processes Overview
Background Processes
