AppSuite:DBMigration

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Revision as of 09:30, 29 August 2014 by Martin.schneider (talk | contribs)


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/ .

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
  • com.openexchange.database.migration.ox: Provides the database migration statements relevant for the Open-Xchange server
  • com.openexchange.database.migration.clt: Provides some command line tools that might help by working with database migration 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.

Preconditions

Preconditions can be used to define dependencies between ChangeSets. You can attach another ChangeSet to whatever ChangeSet you would like to. This will only be executed if the prior was executed successfully. You can create complex conditions by using nested conditions that have to be true to execute the ChangeSet with the precondition.

Open-Xchange uses preconditions for instance for ChangeSets that should be executed after the database has been tagged for a new release. All ChangeSets after tagging checks if the precondition is true.

For further information about that complex function have a look at the following documentation: http://www.liquibase.org/documentation/preconditions.html

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 tools

Currently the following command line tools are available (in bundle com.openexchange.database.migration.clt):

  • /opt/open-xchange/sbin/forcedbmigration: Tries to force the migration for the file provided within the parameters.
  • /opt/open-xchange/sbin/listunexecutedchangesets: Lists currently unexecuted changesets for the file provided within the parameters.
  • /opt/open-xchange/sbin/releasedbmigrationlock: Tries to release the database lock so that Liquibase is able to acquire the lock again. Not releasing the lock might happen when the server was shut down while startup. Using this command line tool includes that com.openexchange.database.migration bundle is running. If it does not get up please execute
<code>UPDATE DATABASECHANGELOGLOCK SET LOCKED=0, LOCKGRANTED=null, LOCKEDBY=null where ID=1;</code>
  • /opt/open-xchange/sbin/rollbackdbmigration: Execute a rollback to the provided database tag. Rollbacks have to be defined for each ChangeSet as for most change statements no autorollback is supported.

Important hints

  • changeSets are uniquely identified by its id, author and path. Use the parameter 'logicalFilePath' for every changeSet you create to set a path that can be globally identified! If you do not set a logical file path Liquibase will use the physical path of the file the changeSet is located in. With that each changeSet on different cluster nodes might have been identified as a new one.
  • 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
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