instructor

Instructor

彭智勇武汉大学软件工程国家重点实验室

电话 :87653196Email: [email protected]

Book

经典原版书库《 Database System Implementation 》

（美） Hator Garcia-Molina, Jeffrey.D.Ullman, Jennifer Widom 著 ( 斯坦福大学 )

机械工业出版社

Marking Scheme

• Assignment (4) ( 练习 ,3 次 ): 15% • Small Test (3) ( 小测验 ,3 次 ): 15%• Final Examination ( 期末考试 ): 70%• Total 100%

Practice

• 安装 PostgreSQL 系统• 分析 PostgreSQL 源代码• 改进 PostgreSQL 系统

http://www.postgresql.org

Database System Implementation

Hector Garcia-MolinaJeffrey D. UllmanJennifer Widom

Chapter 1

Introduction to DBMS Implementation

Database Management System

A database management system (DBMS) is a powerful tool for creating and managing large amounts of data efficiently and allowing it to persist over long periods of time, safely.

Capabilities of a DBMS• Persistent Storage• Programming interface allowing the user to access and modify data

through a powerful query language. • Transaction Management supporting concurrent access to data and

resiliency ( i.e. recovering from failures or errors)

Terminology Review• Data• Database A collection of data, well organized for access and

modification, preserved over a long period.

• Query• Relation An organization of data into a two-dimensional table.

• Schema (Metadata) A description of the structure of the data.

A Simple DBMS: Megatron 2000

Megatron 2000 is a relational database management system which supports the SQL query language.

Megatron 2000 ImplementationThe Relation Students(name, id, dept)

Data: /usr/db/students

Smith#123#CSJohnson#522#EE……

Schema: /usr/db/schema

Students#name#STR#id#INT#dept#STRDepts#name#STR#office#STR……

Execution of Megatron 2000 DBMS

dbhost> megatron2000

WELCOME TO MEGATRON 2000 !

& SELECT *FROM Students #

name id dept

Smith 123 CSJohnson 522 EE

& SELECT *FROM StudentsWHERE id>= 500 | HighID #

/usr/db/HighID

Johnson#522#EE

How Megatron 2000 Executes Queries

SELECT * FROM R WHERE <Condition>

1. Read the file schema to determine the attributes of relation R and their types.2. Check that the <Condition> is semantically valid for R.3. Display each of the attribute names as the header of a column, and draw a line.4. Read the file named R, and for each line: (a) Check the condition, and (b) Display the line as a tuple, if the condition is true.

SELECT * FROM R WHERE <Condition> | T

1. Read the file schema to determine the attributes of relation R and their types.2. Check that the <Condition> is semantically valid for R.3. Read the file named R, and for each line: (a) Check the condition, and (b) Write the result to a new file /usr/db/T, if the condition is true.4. Add to the file /usr/db/schema an entry for T that looks just like the entry for R,

except that relation name T replaces R. That is, the schema for T is the same as the schema for R.

SELECT officeFROM Students, DeptsWHERE Students.name = ‘Smith’ AND Students.dept = Depts.name #

for (each tuple s in Students) for (each tuple d in Depts) if(s and d satisfy the WHERE-condition) display the office value from Depts;

Example 1.2

Problem (1) of Megatron 2000

Tuple layout on disk

The data layout on disk is not flexible. e.g., - Change string from ‘Cat’ to ‘Cats’ and we have to rewrite file

- ASCII storage is expensive- Deletions are expensive


Search expensive; no indexese.g., - Cannot find tuple with given key quickly

- Always have to read full relation


Brute force query processing Query-processing is not clever. e.g., select *

from R,Swhere R.A = S.A and S.B > 1000

- Do select first?- More efficient join?


• No buffer manager

There is no buffer in main memory.e.g., Need caching


There is no concurrency control.


•No reliabilitye.g., - Can lose data

- Can leave operations half done


No securitye.g., - File system insecure

- File system security is coarse


• No application program interface (API)e.g., How can a payroll program get at the data?


• Cannot interact with other DBMSs.


• Poor dictionary facilities


• No GUI

Overview of a Database Management System

Storage

Storagemanager

Buffermanager

Index/file/rec-Ord manager

Executionengine

QueryCompiler Transaction Manager

Logging and Recovery

Buffers

DDL Compiler

Concurrency Control

Locktable

User/application

queries,updates

transaction commands

Databaseadministrator

query plan

Index, file, andrecord requests

page commands

read/write pages

logpages

data,metadata,indexes

metadata statistics metadata

DDL Commands

It is responsible for storing data, metadata, indexes, and logs. An important storage management component is the buffer manager, which keeps portions of the data contents in main memory.

Storage Management

A user or an application program initiates query to extract data from the database. The query is parsed and optimized by a query compiler. The resulting query plan is executed by the execution engine.

Query Processing

Transaction Management

• Logging and Recovery• Concurrency Control• Deadlock Resolution

Course Overview• Storage-Management Overview C2 Memory hierarchy C3 Storage of data elements C4 one-dimensional indexes C5 Multidimensional indexes

• Query ProcessingC6 Query Execution

C7 Query compiler and optimizer

• Transaction-Processing C8 System failures C9 Concurrency control C10 More about transaction management

• Information integration

The course lets students know better ways of building a database management system.

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