Instructor 彭智勇 武汉大学计算机学院珞珈学者特聘教授 软件工程国家重点实验室 电话 :

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

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 S upporting 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#CS Johnson#522#EE …… Schema: /usr/db/schema Students#name#STR#id#INT#dept#STR Depts#name#STR#office#STR ……

Execution of Megatron 2000 DBMS dbhost> megatron2000 WELCOME TO MEGATRON 2000 ! & SELECT * FROM Students # name id dept Smith 123 CS Johnson 522 EE

& SELECT * FROM Students WHERE id>= 500 | HighID # /usr/db/HighID Johnson#522#EE

How Megatron 2000 Executes Queries SELECT * FROM R WHERE 1.Read the file schema to determine the attributes of relation R and their types. 2.Check that the 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 | T 1.Read the file schema to determine the attributes of relation R and their types. 2.Check that the 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 office FROM Students, Depts WHERE 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 indexes e.g.,- Cannot find tuple with given key quickly - Always have to read full relation

Problem (3) of Megatron 2000 Brute force query processing Query-processing is not clever. e.g., select * from R,S where R.A = S.A and S.B > 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 reliability e.g.,- Can lose data - Can leave operations half done

Problem (7) of Megatron 2000 No security e.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 manager Buffer manager Index/file/rec- Ord manager Execution engine Query Compiler Transaction Manager Logging and Recovery Buffers DDL Compiler Concurrency Control Lock table User/application queries, updates transaction commands Database administrator query plan Index, file, and record requests page commands read/write pages log pages 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 Processing C6 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.