AppSuite:DBMigration

This information is valid from 7.6.1 on.

Database migration for Open-Xchange server.

Summary: With release 7.6.1 it is possible to change the database schema based on usage of the open source tool Liquibase. Currently only updating the configdb with the new mechanism is desired. This article gives a short introduction about the current implementation

Please have a look at Liquibase, its features and documentation before working with database migrations for Open-Xchange server: http://www.liquibase.org/documentation/ and http://www.liquibase.org/bestpractices.html .

Ho to create custom bundles is explained in an extra article: http://oxpedia.org/wiki/index.php?title=AppSuite:CustomDBMigration

Database migration bundles

The following bundles provide the functionality for executing database migration statements. All are included within the open-xchange-core package.

• com.openexchange.database.migration: Provides the service to execute database migrations and the core configdb ChangeLog
• com.openexchange.database.migration.clt: Provides a command line tool that might help by working with database migrations based on Liquibase

Current restrictions

• Database migrations can only be applied to the configdb!
• Open-Xchange server currently uses Liquibase version 3.0.7. All features provided with later versions cannot be used.

Liquibase

The following chapter describes shortly the Liquibase features and how they are used by Open-Xchange. For further information have a look at the official Liquibase documentation: http://www.liquibase.org/documentation/

ChangeLog file / changeSets

A ChangeLog file is the heart of this database migration and contains all information required to change database structure and/or contents. It consists of ChangeSets that are used to define a migration. Normally ChangeSets are executed transactionally.

Tags

A ChangeSet can be used to tag the database at a current state. Open-Xchange uses this mechanism to tag the database to be ready for a new release.

Database

Database tables

Liquibase creates two tables to handle its current state:

• LIQUIBASECHANGELOG: Contains information about the execution status of ChangeSets. Each executed ChangeSet will be added to this table. If there is no entry available for a ChangeSet Liquibase will try to execute the statement.
• LIQUIBASECHANGELOGLOCK: Handles access to the database to not execute database migration statements twice.

Database lock

Liquibase uses a lock to only grant one Liquibase instace access to the database to change. For this purpose a table named 'DATABASECHANGELOGLOCK' is created. In cluster environments the first node that successfully aquired the lock will execute the database migration statements. During this time all other nodes are blocked. After the lock was released the second node will get access to the database and read already executed ChangeSets. If all ChangeSets have been executed nothing will be done and the lock will be released. This happens with each node within the cluster.

Custom Java Classes

Implementing CustomSqlChange enables you to write custom SQL statements instead of using declarative statements.

Command line tool

Currently a command line tools is provided to manage the core configdb migrations: /opt/open-xchange/sbin/configdbmigrations

usage: configdbmigrations

-A,--adminuser <arg>   Admin username
-h,--help              Prints a help text
-l,--login <arg>       The optional JMX login (if JMX authentication is
                       enabled)
-ll,--list-locks       Lists all currently acquired locks.
-P,--adminpass <arg>   Admin password
-p,--port <arg>        The optional JMX port (default:9999)
-r,--run               Forces a run of the current core changelog.
-s,--password <arg>    The optional JMX password (if JMX authentication
                       is enabled)
-u,--force-unlock      Forces a release of all locks.

Prints the current migration status if no option is set.

Important hints

• ChangeSets are executed top-down within a ChangeLog, so always add new migrations at the bottom of the file. For migrations regarding core components always use the configdbChangeLog.xml in com.openexchange.database.migration/resource/liquibase. For non-core components see AppSuite:CustomDBMigration.
• ChangeSets must be constructed in an idempotent manner, i.e. they must not fail or break something if they are run several times. Use preconditions with onFail="MARK_RAN" to achieve this.
• If you are adding the first migration for an upcoming release, add an according milestone tag after the actual migration ChangeSets!
• If you would like to use <include> statements to reference other files with Liquibase statements we suggest adding parameter 'relativeToChangelogFile="true"' to avoid adding complete paths.
• http://www.liquibase.org/documentation/sql_output.html