instructor 彭智勇 武汉大学计算机学院珞珈学者特聘教授...
TRANSCRIPT
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 (3) ( 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-Molina
Jeffrey D. Ullman
Jennifer 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 Implementation
The 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
Problem (2) of Megatron 2000
Search expensive; no indexese.g., - Cannot find tuple with given key quickly
- Always have to read full relation
Problem (3) of Megatron 2000
Brute force query processingQuery-processing is not clever.
e.g., select *
from R,S
where R.A = S.A and S.B > 1000
- Do select first?
- More efficient join?
Problem (4) of Megatron 2000
• No buffer manager
There is no buffer in main memory.e.g., Need caching
Problem (5) of Megatron 2000
There is no concurrency control.
Problem (6) of Megatron 2000
•No reliabilitye.g., - Can lose data
- Can leave operations half done
Problem (7) of Megatron 2000
No securitye.g., - File system insecure
- File system security is coarse
Problem (8) of Megatron 2000
• No application program interface (API) e.g.,How can a payroll program get at the data?
Problem (9) of Megatron 2000
• Cannot interact with other DBMSs.
Problem (10) of Megatron 2000
• Poor dictionary facilities
Problem (11) of Megatron 2000
• 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.