This page is for Odysseus developers and shows how to add new recovery techniques to Odysseus.
A recovery technique is in Odysseus a composition of smaller recovery components. Processing Image and BaDaSt are for example two different recovery components. The rollback recovery is a composition of both.
To implement a new recovery component, you have to implement the interface IRecoveryComponent:
IRecoveryComponent
/**
* A recovery component handles the backup and recovery of certain information
* (e.g., installed queries).
*
* @author Michael Brand
*
*/
public interface IRecoveryComponent {
/**
* Initializes the component with a given configuration.
*
* @param config
* the configuration for the component.
*/
public void initialize(Properties config);
/**
* Runs the recovery mechanism for given queries.
*
* @param qbConfig
* The used query build configuration.
* @param session
* The session of the user, who wants to back up the data.
* @param queries
* The queries.
* @param caller
* The executor that called this method.
* @return {@code queries} either modified for recovery or not. Depends on
* the used recovery strategy.
*/
public List<ILogicalQuery> activateRecovery(QueryBuildConfiguration qbConfig, ISession session,
List<ILogicalQuery> queries, IExecutor caller);
/**
* Activates the backup mechanism for given queries.
*
* @param qbConfig
* The used query build configuration.
* @param session
* The session of the user, who wants to back up the data.
* @param queries
* The queries.
* @param caller
* The executor that called this method.
* @return {@code queries} either modified for recovery or not. Depends on
* the used recovery strategy.
*/
public List<ILogicalQuery> activateBackup(QueryBuildConfiguration qbConfig, ISession session,
List<ILogicalQuery> queries, IExecutor caller);
}
To compose a new recovery technique, you have to implement the interface IRecoveryExecutor:
IRecoveryExecutor
/**
* A recovery executor represents a complete non-distributed recovery (NDR)
* strategy by calling certain {@link IRecoveryComponent}s in a certain order.
*
* @author Michael Brand
*
*/
public interface IRecoveryExecutor {
/**
* Gets the name of the executor.
*
* @return A string unique for recovery executors.
*/
public String getName();
/**
* Creates a new recovery executor with a given configuration.
*
* @param config
* the configuration for the executor. Typically, it is the
* totality of configurations for the
* {@link IRecoveryComponent}s.
* @return A new recovery executor instance.
*/
public IRecoveryExecutor newInstance(Properties config);
/**
* Runs the NDR mechanism for given queries.
*
* @param qbConfig
* The used query build configuration.
* @param session
* The session of the user, who wants to recover the data.
* @param queries
* The queries to recover.
* @param caller
* The executor that called this method.
* @return {@code queries} either modified for recovery or not. Depends on
* the used recovery strategy.
*/
public List<ILogicalQuery> activateRecovery(QueryBuildConfiguration qbConfig, ISession session,
List<ILogicalQuery> queries, IExecutor caller);
/**
* Activates the backup mechanism for given queries.
*
* @param qbConfig
* The used query build configuration.
* @param session
* The session of the user, who wants to back up the data.
* @param queries
* The queries to backup.
* @param caller
* The executor that called this method.
* @return {@code queries} either modified for backup or not. Depends on the
* used recovery strategy.
*/
public List<ILogicalQuery> activateBackup(QueryBuildConfiguration qbConfig, ISession session,
List<ILogicalQuery> queries, IExecutor caller);
/**
* Checks, if a recovery is needed.
*
* @return True, if
* {@link #activateRecovery(QueryBuildConfiguration, ISession, List)}
* should be called.
*/
public boolean isRecoveryNeeded();
}
But typically the abstract class AbstractRecoveryExecutor can be used as super class.
After implementing a new recovery executor, it must be declared as an OSGi declarative service that provides an implementation of IRecoveryExecutor.
If you want to use the checkpointing component to get a notification when a checkpoint is reached, you have to register like in the following example:
Usage of Checkpointing
RollbackRecoveryExecutor instance = new RollbackRecoveryExecutor(); List<IRecoveryComponent> components = new ArrayList<>(); components.add(new CheckpointingRecoveryComponent()); components.add(new ProcessingImageRecoveryComponent()); components.add(new BaDaStRecoveryComponent()); components.add(new DuplicatesDetectorRecoveryComponent()); instance.init(config, components); ((CheckpointingRecoveryComponent) instance.components.get(0)) .addCheckpointManagerListener((ProcessingImageRecoveryComponent) instance.components.get(1)); return instance;