IT420: Database Management and Organization

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IT420: Database Management and Organization

Crash Recovery12 April 2006

Adina Crăiniceanuwww.cs.usna.edu/~adina

http://www.cs.usna.edu/~adina

Kroenke, Database Processing 2

Goals

Finish database security Database Recovery

Problems Solutions DBA Tasks


DBA Tasks

Managing database structure Controlling concurrent processing Managing processing rights and responsibilities Developing database security Providing for database recovery Managing the DBMS Maintaining the data repository


Database Security

Database security - only authorized users can perform authorized activities

Developing database security Determine users’ rights and responsibilities

Enforce security requirements using security features from both DBMS and application programs


Application Security

If DBMS security features are inadequate, additional security code could be written in application program Example In Project 2?


SQL Injection Attack

SQL injection attack occurs when data from the user is used to modify a SQL statement

Example: User input: 71111 OR TRUE

SELECT * FROM EMPLOYEEWHERE EMPLOYEE.ID = 71111 OR TRUE;

Result: every row of the EMPLOYEE table will be returned

Check user input !


Database Security Review

Purpose: only authorized users can perform authorized activities

Methods: Run DBMS behind a firewall Apply the latest OS and DBMS service packs and

fixes Use the least functionality possible Protect the computer that runs the DBMS Manage accounts and passwords Write additional security code in application programs


DBA Tasks

Managing database structure Controlling concurrent processing Managing processing rights and responsibilities Developing database security Facilitate database recovery Managing the DBMS Maintaining the data repository


Review: ACID Properties

Atomicity: All actions happen, or none happen

Consistency Isolation Durability: If a transaction commits, its

effects persist

The Recovery Manager guarantees Atomicity & Durability.


Motivation

Atomicity: Transactions may abort (“Rollback”) – need restore

previous state

Durability: DBMS might stop running – need preserve state

Desired behavior after system restarts:T1, T2 & T3 should be durable.T4 & T5 should be aborted (effects not seen).


Basic Idea: Logging

Periodically save the database to disk Keep a transaction log - small

Saved on another disk Contains records of the data changes in

chronological order, for all transactions


Transaction Log


Write-Ahead Logging (WAL)

Must write to log before writing to the database atomicity

Must write all log records for a transaction before commit durability


Class Exercise

Write transaction log entries for the following schedule:

T1: R(Ch) R(Sa), W(Sa), Abort Ch = 100 Sa=1000, Sa=500 T2: R(Ch) R(Sa), W(Sa),

Commit Ch = 100 Sa=1000, Sa=1100


Rollback/Rollforward

When there is a failure: Analyze: figure out which transactions

commited, which failed REDO (Rollforward): restore database using

saved data and re-execute all changes since the last save

UNDO (Rollback): undo the changes made by failed transaction to the database


Rollforward

After-image: a copy of every database record (or page) after it was changed


Rollback

Before-image: a copy of every database record (or page) before it was changed.

Also used for simple transaction

abort


Checkpoint

A checkpoint is a point of synchronization between the database and the transaction log DBMS refuses new requests, finishes processing outstanding

requests, and writes its buffers to disk The DBMS waits until the writing is successfully completed

the log and the database are synchronized Checkpoints speed up database recovery process

Database can be recovered using after-images since the last checkpoint

Checkpoint can be done several times per hour Most DBMS products automatically checkpoint

themselves


Database Recovery:A Processing Problem Occurs


Database Recovery: Recovery Processing


Class Exercise T1: R(Ch) R(Sa), W(Sa), Abort Ch = 100 Sa=1000, Sa=500 T2: R(Ch) R(Sa), W(Sa),

Commit Ch = 100 Sa=1000, Sa=1100

Process crash Analysis REDO UNDO


DBA Tasks for Recovery

Ensure database saves and logs are generated

Periodically backup database Periodically backup log

On disk On tapes


DBA Tasks



Managing the DBMS

Generate database application performance reports

Investigate user performance complaints Assess need for changes in database structure

or application design Modify database structure Evaluate and implement new DBMS features Tune the DBMS


Maintaining the Data Repository DBA is responsible for maintaining the data repository Data repositories are collections of metadata about

users, databases, and its applications The repository may be

Virtual as it is composed of metadata from many different sources: DBMS, code libraries, Web page generation and editing tools, etc.

An integrated product The best repositories are active and they are part of the

system development process


DBA Tasks - Conclusions


IT420: Database Management and Organization

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