Design and Implementation of a Module to Synchronize Databases Amit Hingher Reviewers: Prof. Dr. rer. nat. habil. Andreas Heuer Prof. Dr.-Ing. Hartmut Pfüller Advisor : Dr.-Ing. Holger Meyer Herr Andreas Finger Stefan Dummann (softEnergy GmbH) Master Thesis, University Of Rostock, Germany 23 rd May 2007

Master Thesis, Amit Hingher2 Overview  Introduction  Concept  WIS-Sync - A Prototype  Conclusions & Future Work

Master Thesis, Amit Hingher3 1. Introduction  Data Replication  Wind Information System (WIS)  Motivation  Existing Solution

Master Thesis, Amit Hingher4 What is Data Replication?  Database replication: Process of creating and storing multiple copies of a database with the same data in different locations. Two types of replication-  Synchronous  Asynchronous

Master Thesis, Amit Hingher5 Data Synchronization  Synchronization / Merge replication Keeps the data in two or more locations up-to-date so that each repository contains identical information. Copies data in both directions Used for disconnected environment

Master Thesis, Amit Hingher6 WIS - Wind Information System  An innovative solution for complex analyses and monitoring of power plant data received from energy plants  GUI is provided by a Web server and can be accessed by client through a Web-Browser like IE or Mozilla  Diverse databases running on the server and client i.e. Oracle, Sybase, MySQL  Communication only possible between server and remote replicas and no “inter-replica” communication

Master Thesis, Amit Hingher7 Motivation Local copy WIS Server Local copy No communicati on link Synchronize

Master Thesis, Amit Hingher8 System Overview

Master Thesis, Amit Hingher9 Existing Solution WIS

Master Thesis, Amit Hingher10 Why another solution ?  Dumping whole DB to client  Alternative to log based capture –  A middle-ware replication tool that intercepts command stream between application and database  Synchronization tool relies entirely on transaction log  Cost of maintenance  Currently no manual interaction

Master Thesis, Amit Hingher11 2. Concept  Proposed System  WIS-Sync: A 3-Step Process  Capture process  Merge Process - Conflict Resolution  Table Filtering  Incremental progress  Manual resolution

Master Thesis, Amit Hingher12 WIS-Sync: A 3-Step Process

Master Thesis, Amit Hingher13 Golding’s Timestamp Anti-Entropy Protocol  Updates are propagated via anti-entropy sessions in which two replicas exchange the content of their logs

Master Thesis, Amit Hingher14 WIS-Sync: Capture Process

Master Thesis, Amit Hingher15 Conflict Resolution - Basics  A conflict is said to arise when rows with same unique ID from the same tables are updated on different databases  Resolution option used:  Server- Wins  Client-Wins

Master Thesis, Amit Hingher16 Conflict Scenario - 1  Insert – Insert

Master Thesis, Amit Hingher17 Conflict Scenario - 2  Update - Delete

Master Thesis, Amit Hingher18 Conflict Scenario - 3  Update-Update

Master Thesis, Amit Hingher19 WIS-Sync: Merge Process

Master Thesis, Amit Hingher20 Table-Filtering  Allows user to select the tables he wants to synchronize  Provides maximum flexibility  User has full control over the system thus avoiding any unnecessary updates

Master Thesis, Amit Hingher21 Incremental Progress

Master Thesis, Amit Hingher22 Violations – An Example

Master Thesis, Amit Hingher23 How has this research helped ?  Features & Improvements  Capture Process - “direct-to-database” method  Table filtering  Conflict Resolution  Incremental progress  Manual resolution  Support for heterogeneous databases

Master Thesis, Amit Hingher24 3. WIS-Sync : A Prototype

Master Thesis, Amit Hingher25 OJB – ObJect Relational Bridge  Apache (OJB) is an Object/Relational mapping tool that allows transparent persistence for Java Objects against relational databases.  Supports the following DB’s: MSSQL MySQL Oracle MS Access PostgreSQL Informix Sybase MaxDB

Master Thesis, Amit Hingher26 O/R Mapping

Master Thesis, Amit Hingher27 WIS-Sync: Class Diagram

Master Thesis, Amit Hingher28 WIS-Sync: Configuration Page

Master Thesis, Amit Hingher29 3. Conclusions  No general solution available toward synchronization  Principal goal of an update propagation strategy is to ensure internal and mutual consistency  “Direct-to-database” approach can prove to be an alternative to log-based capture  O/R Mapping can be used in scenarios where compatibility between diverse databases is needed.

Master Thesis, Amit Hingher30 Future Work  User-friendly GUI Interface  Multiple users synchronizing  Could be implemented for a mobile as well.

Master Thesis, Amit Hingher31 Thank you all !!!