racle 9i學習日誌（4）--邏輯結構與習題解析

Logical Structure

 

在oracle database中數據時存儲在tablespaces（表空間）裏的，一個表空間只能屬於一個database，一個表空間可以對應一個或多個物理文件（data file）。

一個oracle server上只有一個database，一個database包含至少一個表空間，一個表空間包含一個或多個段，一段由多個extent組成，extent由許多連續的塊（block）組成。

一個segment不能跨越表空間，但一個segment可以屬於不同的data file。但一個extent不能跨越data file。

data block是oracle server分配，讀寫等基本操作的最小存儲單元，大小由DB_BLOCK_SIZE這個參數指定，但必須是操作系統block的整數倍，最大尺寸不同的系統不同。

SQL語句的處理過程

處理一個查詢：

1.解析：

       -查找相同的語句

       -檢查語法，目標名，權限

       -Lock objects used during parse

       -創建和存儲執行計劃

2.綁定：得到一個變量

3.執行：

4.返回：返回結果

處理DML語句，處理DDL語句：

基本過程類似，可分爲連接，安全檢查，解析，綁定變量，執行，返回結果。

 

Practice 1: Oracle Architectural Components
1 Which one of the following statements is true?
a An Oracle server is a collection of data consisting of three file types.
b A user establishes a connection with the database by starting an Oracle instance.
c A connection is a communication pathway between the Oracle server and the Oracle instance.
d A session starts when a user is validated by the Oracle server.
答案：d。

解析：a，這是對database files的描述，而不是oracle server。b，一個oracle server只會啓動一個instance，user直接與server process打交道而不是instance，一般來說一個connection對應一個server process。c，參考“我的學習筆記（3）”可知，這是對session的描述，而不是connection。d，正確。

2 Which one of the following memory areas is not part of the SGA?
a Database Buffer Cache
b PGA
c Redo Log Buffer
d Shared Pool
答案：b。

3 Which two of the following statements are true about the Shared Pool?
a The Shared Pool consists of the Library Cache, Data Dictionary Cache, Shared  SQL area, Java Pool, and Large Pool.
b The Shared Pool is used to store the most recently executed SQL statements.
c The Shared Pool is used for an object that can be shared globally.
d The Library Cache consists of the Shared SQL and Shared PL/SQL areas.

答案：b，d。

解析：c答案在oracle教材上有這樣的話“Because the Shared Pool is used for objects that can be shared globally”，但在這個題目中有歧義，c，d兩項最佳答案是d。

4 Which one of the following memory areas is used to cache the data dictionary
information?
a Database Buffer Cache
b PGA
c Redo Log Buffer
d Shared Pool

答案：d。

5 The primary purpose of the Redo Log Buffer is to record all changes to the database
data blocks.
a True
b False

答案：a。

6 The PGA is a memory region that contains data and control information for multiple
server processes or multiple background processes.
a True
b False

答案：b。

解析：不是multiple，是single。一個PGA對應一個進程。

7 Which of the following becomes available when an Oracle instance is started?
a User process
b Server process
c Background processes

答案：c。

8 Identify five mandatory background processes.
答案：DBWn,LGWR,SMON,PMON,CKPT

9 Match the process with its task.
a Database Writer          1 Assists with writing to the data file headers
b Log Writer                     2 Is responsible for instance recovery
c System Monitor            3 Cleans up after failed processes
d Process Monitor          4 Records database changes for recovery purposes
e Checkpoint                   5 Writes dirty buffers to the data files

答案：a-5,b-4,c-2,d-3,e-1。

10 The physical structure of an Oracle database consists of control files, data files, and
online redo log files.
a True
b False

答案：a。

11 Place the following structures in order of hierarchy beginning with database.
a Tablespaces
b Extent
c Segment
d Database
e Block

答案：從小到大順序：e,b,c,a,d.

12 Identify the components of an Oracle server.
答案：database，instance。

13 Identify the components of an Oracle instance.
答案：內存結構（或SGA）和後臺進程
 

14 Identify three file types that make up an Oracle database.
答案：data files，control files，redo log files。