Download Introduction - Clemson University

CpSc 8620: DBMS Design
Introduction
Attribution
Materials and lecture notes in this course are
adapted from various sources, including the
authors of the textbook and references,
Internet, instructor’s personal notes,
instructor’s friends, etc.
The instructor has tried to attribute all
authors of the course materials.
If you think that the instructor may overlook
something, please tell the instructor.
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Class Issues
Instructor:
Dr. Feng Luo, Associate professor
school of computing
210 McAdams Hall
Office: (864) 656 4793
E-mail: [email protected]
Class web:
http://www.cs.clemson.edu/~luofeng/course/Databas
eSystem/database.html
Class hours:
4:00 PM -5:15 PM, MW
Office hours:
1:00PM – 2:00PM, MW
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Q&A:
Send questions to [email protected]
Homework
You must finish your homework
assignments independently. Any form of
cheating will result in 0 point on that
assignment for both parties.
You must submit your homework at the due
date. Late submission will not be accepted
unless being approved by instructor.
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You will not get your submitted homework
assignments back during the semester.
Instead, I will post the homework solutions
regularly to help you comprehend the
course content. If you have any questions
regarding your grades, you need to talk to
me by appointment.
Grading Policy
Homework (20%): Programming, reviewing papers, and written
assignments.
Midterm Exam (20%): Cover the contents studied in first half of the
semester.
Final Exam (20%): Cover the contents studied in second half of the
semester.
Project (40%): The projects will be assigned the first half of the
semester.
Grading: A (90 - 100), B (80 - 89), C (70 - 79), D (60 - 69), F (0 - 59).
(The scale may be curved down at the end of the semester if needed)
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http://www.economist.com/specialreports/displaystory.cfm?story_id=15557443
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How much data are there in the
world?
From the beginning of recorded time until
2003 we created 5 billion gigabytes
(exabytes) of data.
In 2011 the same amount was created every
two days.
In 2013, the same amount is created every
10 minutes.
http://money.cnn.com/gallery/technology/2
012/09/10/big-data.fortune/index.html
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Characteristics of Data
• Computing power doubles every 18 months (Moore’s
Law) ...
Moore’s Law
• 100x improvement in 10 years
of Slacking
• The amount of data doubles every year ...will not help !
• 1000x in 10 years, and 1,000,000x in 20 yrs.
http://arxiv.org/abs/astro-ph/9912202
• I/O bandwidth increases ~10% / year
• <3x improvement in 10 years.
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What Is a DBMS?
A very large, integrated collection of data.
Models real-world.
Entities (e.g., students, courses)
Relationships (e.g., Jane is taking CpSc 862)
A Database Management System (DBMS) is
a software package designed to store and
manage databases.
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Why Use a DBMS?
Data independence and efficient access.
Reduced application development time.
Data integrity and security.
Uniform data administration.
Concurrent access, recovery from crashes.
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Why Study Databases??
Shift from computation to information
at the “low end”: scramble to webspace (a
mess!)
at the “high end”: scientific applications
Datasets increasing in diversity and volume.
Digital libraries, interactive video, Human
Genome project, EOS project
... need for DBMS exploding
DBMS encompasses most of CS
OS, languages, theory, “A”I, multimedia, logic
Most CS jobs are database related.
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Data Models
A data model is a collection of concepts
for describing data.
A schema is a description of a particular
collection of data, using the a given data
model.
The relational model of data is the most
widely used model today.
Main concept: relation, basically a table with
rows and columns.
Every relation has a schema, which describes
the columns, or fields.
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Levels of Abstraction
Many views, single
conceptual (logical)
schema and physical
schema.
View 1
Views describe how users
see the data.
Conceptual schema defines
logical structure
Physical schema describes
the files and indexes used.
View 2
View 3
Conceptual Schema
Physical Schema
* Schemas are defined using DDL; data is modified/queried using DML.
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Example: University Database
Conceptual schema:
Students(sid: string, name: string, login: string,
age: integer, gpa:real)
Courses(cid: string, cname:string,
credits:integer)
Enrolled(sid:string, cid:string, grade:string)
Physical schema:
Relations stored as unordered files.
Index on first column of Students.
External Schema (View):
Course_info(cid:string,enrollment:integer)
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Data Independence
Applications isolated from how data is
structured and stored.
Logical data independence: Protection from
changes in logical structure of data.
Physical data independence: Protection
from changes in physical structure of data.
* One of the most important benefits of using a DBMS!
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Concurrency Control
Concurrent execution of user programs
is essential for good DBMS performance.
Because disk accesses are frequent, and
relatively slow, it is important to keep the cpu
humming by working on several user programs
concurrently.
Interleaving actions of different user
programs can lead to inconsistency: e.g.,
check is cleared while account balance is
being computed.
DBMS ensures such problems don’t arise:
users can pretend they are using a singleuser system.
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Transaction: An Execution of a DB
Program
Key concept is transaction, which is an atomic
sequence of database actions (reads/writes).
Each transaction, executed completely, must leave
the DB in a consistent state if DB is consistent
when the transaction begins.
Users can specify some simple integrity constraints on
the data, and the DBMS will enforce these constraints.
Beyond this, the DBMS does not really understand the
semantics of the data. (e.g., it does not understand how
the interest on a bank account is computed).
Thus, ensuring that a transaction (run alone) preserves
consistency is ultimately the user’s responsibility!
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Ensuring Atomicity
DBMS ensures atomicity (all-or-nothing
property) even if system crashes in the
middle of a Xact.
Idea: Keep a log (history) of all actions
carried out by the DBMS while executing a
set of Xacts:
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Before a change is made to the database, the
corresponding log entry is forced to a safe
location. (WAL protocol; OS support for this is
often inadequate.)
After a crash, the effects of partially executed
transactions are undone using the log. (Thanks
to WAL, if log entry wasn’t saved before the
crash, corresponding change was not applied to
database!)
The Log
The following actions are recorded in the log:
Ti writes an object: the old value and the new value.
Log record must go to disk before the changed page!
Ti commits/aborts: a log record indicating this action.
Log records chained together by Xact id, so it’s easy
to undo a specific Xact (e.g., to resolve a deadlock).
Log is often duplexed and archived on “stable”
storage.
All log related activities (and in fact, all CC related
activities such as lock/unlock, dealing with
deadlocks etc.) are handled transparently by the
DBMS.
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Databases make these folks
happy ...
End users and DBMS vendors
DB application programmers
E.g. smart webmasters
Database administrator (DBA)
Designs logical /physical schemas
Handles security and authorization
Data availability, crash recovery
Database tuning as needs evolve
Must understand how a DBMS works!
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Structure of a DBMS
A typical DBMS has a
layered architecture.
The figure does not
show the concurrency
control and recovery
components.
This is one of several
possible architectures;
each system has its
own variations.
These layers must
consider concurrency
control and recovery
Query Optimization
and Execution
Relational Operators
Files and Access Methods
Buffer Management
Disk Space Management
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DB
Summary
DBMS used to maintain, query large datasets.
Benefits include recovery from system crashes,
concurrent access, quick application
development, data integrity and security.
Levels of abstraction give data independence.
A DBMS typically has a layered architecture.
DBAs hold responsible jobs and are well-paid!
DBMS R&D is one of the broadest,
most exciting areas in CS.
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What are we going to learn?
It is not about how to use database systems. To learn
database systems, read Oracle, SQL Server or MySQL
manual.
It is not about database programming. study CpSc
462/662 for database programming.
Focus on DBMS design and implementation.
You will arguably be a better database user or
programmer if you have an understanding of what is
going on "under the hood".
You will definitely be better prepared for database
research after completing this course.
A lot of advanced topics.
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Class Topics (not limit to)
File System & Storage System.
Indexing & Hashing.
Query Processing.
Transaction Processing.
Concurrency Control.
Logging and Recovery.
Distributed Database Systems.
NoSQL Database
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Course Objectives
This course will provide the students with an
overview of DBMS technologies and the latest
developments in DBMS systems.
Students will be able to gain valuable hands on
experience in DBMS design and implementation.
Recent database papers or technique reports will be
presented or assigned as homework
Upon completion of the class, the students will be
able to:
Comprehend database system fundamentals, including
storage systems, indexing mechanisms, memory
management, etc.
Design and implement a DBMS system or identify a
problem in certain database area and provide a
reasonable solution.
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References
Database Systems: The Complete Book, Second Edition, Hector
Garcia-Molina, Jeffrey D. Ullman, Jennifer D. Widom, Prentice
Hall, 2008, ISBN: 0-13-187325-3. (Textbook)
Database Management Systems, Third Edition, Raghu
Ramakrishnan and Johannes Gehrke, McGraw-Hill, 2002, ISBN:
0-07-246563-8.
Fundamentals of Database Systems, Sixth Edition, Ramez
Elmasri, Shamkant B. Navathe, Addison Wesley, 2010, ISBN: 0136-08620-9.
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