©Silberschatz, Korth and Sudarshan1.1Database System Concepts - 6 th Edition Database System Concepts

©Silberschatz, Korth and Sudarshan1.2Database System Concepts - 6 th Edition Top 10 Largest Databases 2013 By Siliconindia News The World Data Centre for Climate (WDCC): 220 terabytes of data, plus 110 terabytes of data for climate simulation, and 6 petabytes of extra data stored in magnetic tapes. National Energy Research Scientific Computing Center (NERSC) 2.8 petabytes AT&T: It has the largest volume of data in one unique database, with the most number of rows, 1.9 trillion. Google: Google accounts every single search that makes each day into its database which is around 91 million searches per day. Sprint (Telecom company) LexisNexis Youtube Amazon Central Intelligence Agency (CIA) Library of Congress (USA)

©Silberschatz, Korth and Sudarshan1.3Database System Concepts - 6 th Edition Database Management System (DBMS) DBMS contains information about a particular enterprise Collection of interrelated data Set of programs to access the data An environment that is both convenient and efficient to use Database Applications: Banking: transactions Airlines: reservations, schedules Universities: registration, grades Sales: customers, products, purchases Online retailers: order tracking, customized recommendations Manufacturing: production, inventory, orders, supply chain Human resources: employee records, salaries, tax deductions Databases touch all aspects of our lives

©Silberschatz, Korth and Sudarshan1.4Database System Concepts - 6 th Edition Database Landscape Map – June 2013

©Silberschatz, Korth and Sudarshan1.5Database System Concepts - 6 th Edition Google Data Center Google Cloud SQL allows users to use relational database in Google’s Cloud.

©Silberschatz, Korth and Sudarshan1.6Database System Concepts - 6 th Edition Taken from a talk given by Dr. Wen-Syan Li (VP of SAP) SAP HANA SAP HANA is an in-memory relational database system.

©Silberschatz, Korth and Sudarshan1.7Database System Concepts - 6 th Edition Taken from a talk given by Dr. Wen-Syan Li (VP of SAP)

©Silberschatz, Korth and Sudarshan1.8Database System Concepts - 6 th Edition Taken from a talk given by Dr. Wen-Syan Li (VP of SAP)

©Silberschatz, Korth and Sudarshan1.9Database System Concepts - 6 th Edition Amazon Web Services (AWS) Amazon RDS: a relational database server with minimal administration, using MySQL, Oracle, or SQL Server. Amazon DynamoDB: a fast highly scalable NoSQL database service. Amazon SimpleDB: A NoSQL database service for smaller dataasets Amazon EC2 and EBS: A relational database you can manage on your own. EC2: Amazon Elastic Compute Cloud EBS: Amazon Elastic Block Storage

©Silberschatz, Korth and Sudarshan1.10Database System Concepts - 6 th Edition Relational Model Relational model (Chapter 2) Example of tabular data in the relational model Columns Rows

©Silberschatz, Korth and Sudarshan1.11Database System Concepts - 6 th Edition Schemas and Instances Schema Schema – the logical structure of the database (like variables) Example: The database consists of information about a set of customers and accounts and the relationship between them Physical schema: database design at the physical level (how we store data on disk for system to fast access data) Logical schema: database design at the logical level (how users see the data format in order to access data) Instance – the actual content of the database (like values) Physical Data Independence – the ability to modify the physical schema without changing the logical schema Applications depend on the logical schema Changes in some parts do not seriously influence others.

©Silberschatz, Korth and Sudarshan1.12Database System Concepts - 6 th Edition Data Definition Language (DDL) Specification notation for defining the database schema Example:create table instructor ( ID char(5), name char(20), dept_name char(20), salary numeric(8,2)) DDL compiler generates a set of tables stored in a data dictionary

©Silberschatz, Korth and Sudarshan1.13Database System Concepts - 6 th Edition Data Manipulation Language (DML) Language for accessing and manipulating the data organized by the appropriate data model DML also known as query language SQL is the most widely used query language Users specifies what data is required and how to get those data

©Silberschatz, Korth and Sudarshan1.14Database System Concepts - 6 th Edition SQL Find the name of the instructor with ID selectname frominstructor whereinstructor.ID = ‘22222’ Find all instructor IDs if they are in a department whose budget > select instructor.ID, department.dept_name from instructor, department where instructor.dept_name= department.dept_name and department.budget > Application programs generally access databases through one of Language extensions to allow embedded SQL Application program interface (e.g., ODBC/JDBC) which allow SQL queries to be sent to a database

©Silberschatz, Korth and Sudarshan1.15Database System Concepts - 6 th Edition Storage Management Storage manager provides the interface between the low-level data stored in the database and the application programs and queries submitted to the system. The storage manager is responsible to efficient storing, retrieving and updating of data Issues: Storage access File organization Indexing and hashing

©Silberschatz, Korth and Sudarshan1.16Database System Concepts - 6 th Edition Query Processing 1.Parsing and translation 2.Optimization 3.Evaluation

©Silberschatz, Korth and Sudarshan1.17Database System Concepts - 6 th Edition Query Processing (Cont.) Alternative ways of evaluating a given query Equivalent expressions Different algorithms for each operation Cost difference between a good and a bad way of evaluating a query can be enormous Need to estimate the cost of operations Depends critically on statistical information about relations which the database must maintain Need to estimate statistics for intermediate results to compute cost of complex expressions

©Silberschatz, Korth and Sudarshan1.18Database System Concepts - 6 th Edition Atomicity of Updates & Concurrent Access Atomicity of updates Failures may leave database in an inconsistent state with partial updates carried out Example: Transfer of funds from one account to another should either complete or not happen at all Concurrent access by multiple users Uncontrolled concurrent accesses can lead to inconsistencies  Example: Two people reading a balance (say 100) and updating it by withdrawing money (say 50 each) at the same time Concurrent access needed for performance

©Silberschatz, Korth and Sudarshan1.19Database System Concepts - 6 th Edition Transaction Management To deal with the system fails. To control when many users concurrently update the same data. A transaction is a collection of operations that performs a single logical function in a database application Transaction-management component ensures that the database remains in a consistent (correct) state despite system failures (e.g., power failures and operating system crashes) and transaction failures. Concurrency-control manager controls the interaction among the concurrent transactions, to ensure the consistency of the database.

©Silberschatz, Korth and Sudarshan1.20Database System Concepts - 6 th Edition Database System Internals