Package com.db4o.config

Interface Configuration

  • All Known Implementing Classes:
    Config4Impl
    public interface Configuration
    configuration interface.

    This interface contains methods to configure db4o.

    The global Configuration context is available with Db4o.configure(). When an ObjectContainer or ObjectServer is opened, the global Configuration context is cloned and copied into the ObjectContainer/ObjectServer. That means every ObjectContainer/ObjectServer gets it's own copy of configuration settings.

    Most configuration settings should be set before opening an ObjectContainer/ObjectServer.

    Some configuration settings can be modified on an open ObjectContainer/ObjectServer. The local Configuration context is available with ExtObjectContainer.configure() and ExtObjectServer.configure().

    • Method Detail

      • activationDepth

        void activationDepth​(int depth)
        sets the activation depth to the specified value.

        Why activation?
        When objects are instantiated from the database, the instantiation of member objects needs to be limited to a certain depth. Otherwise a single object could lead to loading the complete database into memory, if all objects where reachable from a single root object.

        db4o uses the concept "depth", the number of field-to-field hops an object is away from another object. The preconfigured "activation depth" db4o uses in the default setting is 5.

        Whenever an application iterates through the ObjectSet of a query result, the result objects will be activated to the configured activation depth.

        A concrete example with the preconfigured activation depth of 5:
         // Object foo is the result of a query, it is delivered by the ObjectSet 
 Object foo = objectSet.next();
        foo.member1.member2.member3.member4.member5 will be a valid object
        foo, member1, member2, member3 and member4 will be activated
        member5 will be deactivated, all of it's members will be null
        member5 can be activated at any time by calling ObjectContainer.activate(Object, int).

        Note that raising the global activation depth will consume more memory and have negative effects on the performance of first-time retrievals. Lowering the global activation depth needs more individual activation work but can increase performance of queries.

        ObjectContainer.deactivate(Object, int) can be used to manually free memory by deactivating objects.

        In client/server environment the same setting should be used on both client and server

        .
        Parameters:
        depth - the desired global activation depth.
        See Also:
        configuring classes individually

      • activationDepth

        int activationDepth()
        gets the configured activation depth.
        Returns:
        the configured activation depth.

      • add

        void add​(ConfigurationItem configurationItem)
        adds ConfigurationItems to be applied when an ObjectContainer or ObjectServer is opened.
        Parameters:
        configurationItem - the ConfigurationItem

      • addAlias

        void addAlias​(Alias alias)
        adds a new Alias for a class, namespace or package.

        Aliases can be used to persist classes in the running application to different persistent classes in a database file or on a db4o server.

        Two simple Alias implementations are supplied along with db4o:
        - TypeAlias provides an #equals() resolver to match names directly.
        - WildcardAlias allows simple pattern matching with one single '*' wildcard character.

        It is possible to create own complex Alias constructs by creating own resolvers that implement the Alias interface.

        Examples of concrete usecases:

        EmbeddedConfiguration config = Db4oEmbedded.newConfiguration();
        // Creating an Alias for a single class
        config.common().addAlias(
          new TypeAlias("com.f1.Pilot", "com.f1.Driver"));


        // Mapping a Java package onto another
        config.common().addAlias(
          new WildcardAlias(
            "com.f1.*",
            "com.f1.client*"));

        Aliases that translate the persistent name of a class to a name that already exists as a persistent name in the database (or on the server) are not permitted and will throw an exception when the database file is opened.

        Aliases should be configured before opening a database file or connecting to a server.

        In client/server environment this setting should be used on the server side.

      • removeAlias

        void removeAlias​(Alias alias)
        Removes an alias previously added with addAlias(Alias).
        Parameters:
        alias - the alias to remove

      • allowVersionUpdates

        void allowVersionUpdates​(boolean flag)
        turns automatic database file format version updates on.

        Upon db4o database file format version changes, db4o can automatically update database files to the current version. db4objects does not provide functionality to reverse this process. It is not ensured that updated database files can be read with older db4o versions. In some cases (Example: using ObjectManager) it may not be desirable to update database files automatically therefore automatic updating is turned off by default for security reasons.

        Call this method to turn automatic database file version updating on.

        If automatic updating is turned off, db4o will refuse to open database files that use an older database file format.

        In client-server environment this setting should be used on both client and server.

      • automaticShutDown

        void automaticShutDown​(boolean flag)
        turns automatic shutdown of the engine on and off. The default and recommended setting is true.

        In client-server environment this setting should be used on both client and server.
        Parameters:
        flag - whether db4o should shut down automatically.

      • blockSize

        void blockSize​(int bytes)
        throws GlobalOnlyConfigException
        sets the storage data blocksize for new ObjectContainers.

        The standard setting is 1 allowing for a maximum database file size of 2GB. This value can be increased to allow larger database files, although some space will be lost to padding because the size of some stored objects will not be an exact multiple of the block size. A recommended setting for large database files is 8, since internal pointers have this length.

        This setting is only effective when the database is first created, in client-server environment in most cases it means that the setting should be used on the server side.
        Parameters:
        bytes - the size in bytes from 1 to 127
        Throws:
        GlobalOnlyConfigException

      • bTreeNodeSize

        void bTreeNodeSize​(int size)
        configures the size of BTree nodes in indexes.

        Default setting: 100
        Lower values will allow a lower memory footprint and more efficient reading and writing of small slots.
        Higher values will reduce the overall number of read and write operations and allow better performance at the cost of more RAM use.

        This setting should be used on both client and server in client-server environment.
        Parameters:
        size - the number of elements held in one BTree node.

      • bTreeCacheHeight

        void bTreeCacheHeight​(int height)
        configures caching of BTree nodes.

        Clean BTree nodes will be unloaded on #commit and #rollback unless they are configured as cached here.

        Default setting: 0
        Possible settings: 1, 2 or 3

        The potential number of cached BTree nodes can be calculated with the following formula:
        maxCachedNodes = bTreeNodeSize ^ bTreeCacheHeight

        This setting should be used on both client and server in client-server environment.
        Parameters:
        height - the height of the cache from the root

      • callbacks

        void callbacks​(boolean flag)
        turns callback methods on and off.

        Callbacks are turned on by default.

        A tuning hint: If callbacks are not used, you can turn this feature off, to prevent db4o from looking for callback methods in persistent classes. This will increase the performance on system startup.

        In client/server environment this setting should be used on both client and server.
        Parameters:
        flag - false to turn callback methods off
        See Also:
        Using callbacks

      • callConstructors

        void callConstructors​(boolean flag)
        advises db4o to try instantiating objects with/without calling constructors.

        Not all JDKs / .NET-environments support this feature. db4o will attempt, to follow the setting as good as the enviroment supports. In doing so, it may call implementation-specific features like sun.reflect.ReflectionFactory#newConstructorForSerialization on the Sun Java 1.4.x/5 VM (not available on other VMs) and FormatterServices.GetUninitializedObject() on the .NET framework (not available on CompactFramework). This setting may also be overridden for individual classes in ObjectClass.callConstructor(boolean).

        The default setting depends on the features supported by your current environment.

        In client/server environment this setting should be used on both client and server.

        Parameters:
        flag - - specify true, to request calling constructors, specify false to request not calling constructors.
        See Also:
        ObjectClass.callConstructor(boolean)

      • classActivationDepthConfigurable

        void classActivationDepthConfigurable​(boolean flag)
        turns individual class activation depth configuration on and off.

        This feature is turned on by default.

        In client/server environment this setting should be used on both client and server.

        Parameters:
        flag - false to turn the possibility to individually configure class activation depths off
        See Also:
        Why activation?

      • databaseGrowthSize

        void databaseGrowthSize​(int bytes)
        configures the size database files should grow in bytes, when no free slot is found within.

        Tuning setting.

        Whenever no free slot of sufficient length can be found within the current database file, the database file's length is extended. This configuration setting configures by how much it should be extended, in bytes.

        This configuration setting is intended to reduce fragmentation. Higher values will produce bigger database files and less fragmentation.

        To extend the database file, a single byte array is created and written to the end of the file in one write operation. Be aware that a high setting will require allocating memory for this byte array.
        Parameters:
        bytes - amount of bytes

      • detectSchemaChanges

        void detectSchemaChanges​(boolean flag)
        tuning feature: configures whether db4o checks all persistent classes upon system startup, for added or removed fields.

        If this configuration setting is set to false while a database is being created, members of classes will not be detected and stored.

        This setting can be set to false in a production environment after all persistent classes have been stored at least once and classes will not be modified any further in the future.

        In a client/server environment this setting should be configured both on the client and and on the server.

        Default value: true
        Parameters:
        flag - the desired setting

      • diagnostic

        DiagnosticConfiguration diagnostic()
        returns the configuration interface for diagnostics.
        Returns:
        the configuration interface for diagnostics.

      • disableCommitRecovery

        void disableCommitRecovery()
        turns commit recovery off.

        db4o uses a two-phase commit algorithm. In a first step all intended changes are written to a free place in the database file, the "transaction commit record". In a second step the actual changes are performed. If the system breaks down during commit, the commit process is restarted when the database file is opened the next time. On very rare occasions (possibilities: hardware failure or editing the database file with an external tool) the transaction commit record may be broken. In this case, this method can be used to try to open the database file without commit recovery. The method should only be used in emergency situations after consulting db4o support.

      • encrypt

        void encrypt​(boolean flag)
      throws GlobalOnlyConfigException
        Deprecated.
        use a custom encrypting IoAdapter instead
        configures the use of encryption.

        This method needs to be called before a database file is created with the first Db4o.openFile(java.lang.String).

        If encryption is set to true, you need to supply a password to seed the encryption mechanism.

        db4o database files keep their encryption format after creation.

        Parameters:
        flag - true for turning encryption on, false for turning encryption off.
        Throws:
        GlobalOnlyConfigException
        See Also:
        password(java.lang.String)

      • exceptionsOnNotStorable

        void exceptionsOnNotStorable​(boolean flag)
        configures whether Exceptions are to be thrown, if objects can not be stored.

        db4o requires the presence of a constructor that can be used to instantiate objects. If no default public constructor is present, all available constructors are tested, whether an instance of the class can be instantiated. Null is passed to all constructor parameters. The first constructor that is successfully tested will be used throughout the running db4o session. If an instance of the class can not be instantiated, the object will not be stored. By default, execution will continue without any message or error. This method can be used to configure db4o to throw an ObjectNotStorableException if an object can not be stored.

        The default for this setting is true.

        In client/server environment this setting should be used on both client and server.

        Parameters:
        flag - false to not throw Exceptions if objects can not be stored (fail silently).

      • generateUUIDs

        void generateUUIDs​(ConfigScope setting)
        configures db4o to generate UUIDs for stored objects. This setting should be used when the database is first created.

        Parameters:
        setting - the scope for UUID generation: disabled, generate for all classes, or configure individually

      • generateVersionNumbers

        @Deprecated
void generateVersionNumbers​(ConfigScope setting)
        Deprecated.
        As of version 8.0 please use generateCommitTimestamps(boolean) instead.
        configures db4o to generate version numbers for stored objects. This setting should be used when the database is first created.
        Parameters:
        setting - the scope for version number generation: disabled, generate for all classes, or configure individually

      • generateCommitTimestamps

        void generateCommitTimestamps​(boolean flag)
        Configures db4o to generate commit timestamps for all stored objects.

        All the objects commited within a transaction will share the same commit timestamp.
        This setting should be used when the database is first created.

        Afterwards you can access the object's commit timestamp like this:

         ObjectContainer container = ...;
 ObjectInfo objectInfo = container.ext().getObjectInfo(obj);
 long commitTimestamp = objectInfo.getVersion();
        Parameters:
        flag - if true, commit timetamps will be generated for all stored objects. If you already have commit timestamps for stored objects and later set this flag to false, although you wont be able to access them, the commit timestamps will still be taking space in your file container. The only way to free that space is defragmenting the container.
        Since:
        8.0

      • internStrings

        void internStrings​(boolean flag)
        configures db4o to call #intern() on strings upon retrieval. In client/server environment the setting should be used on both client and server.
        Parameters:
        flag - true to intern strings

      • internStrings

        boolean internStrings()
        returns true if strings will be interned.

      • markTransient

        void markTransient​(java.lang.String attributeName)
        allows to mark fields as transient with custom attributes.

        .NET only: Call this method with the attribute name that you wish to use to mark fields as transient. Multiple transient attributes are possible by calling this method multiple times with different attribute names.

        In client/server environment the setting should be used on both client and server.

        Parameters:
        attributeName - - the fully qualified name of the attribute, including it's namespace

      • messageLevel

        void messageLevel​(int level)
        sets the detail level of db4o messages. Messages will be output to the configured output PrintStream.

        Level 0 - no messages
        Level 1 - open and close messages
        Level 2 - messages for new, update and delete
        Level 3 - messages for activate and deactivate

        When using client-server and the level is set to 0, the server will override this and set it to 1. To get around this you can set the level to -1. This has the effect of not returning any messages.

        In client-server environment this setting can be used on client or on server depending on which information do you want to track (server side provides more detailed information).

        Parameters:
        level - integer from 0 to 3
        See Also:
        setOut(java.io.PrintStream)

      • lockDatabaseFile

        void lockDatabaseFile​(boolean flag)
        can be used to turn the database file locking thread off.

        Since Java does not support file locking up to JDK 1.4, db4o uses an additional thread per open database file to prohibit concurrent access to the same database file by different db4o sessions in different VMs.

        To improve performance and to lower ressource consumption, this method provides the possibility to prevent the locking thread from being started.

        Caution!
        If database file locking is turned off, concurrent write access to the same database file from different JVM sessions will corrupt the database file immediately.

        This method has no effect on open ObjectContainers. It will only affect how ObjectContainers are opened.

        The default setting is true.

        In client-server environment this setting should be used on both client and server.

        Parameters:
        flag - false to turn database file locking off.

      • objectClass

        ObjectClass objectClass​(java.lang.Object clazz)
        returns an ObjectClass object to configure the specified class.

        The clazz parameter can be any of the following:
        - a fully qualified classname as a String.
        - a Class object.
        - any other object to be used as a template.

        Parameters:
        clazz - class name, Class object, or example object.

        Returns:
        an instance of an ObjectClass object for configuration.

      • optimizeNativeQueries

        void optimizeNativeQueries​(boolean optimizeNQ)
        If set to true, db4o will try to optimize native queries dynamically at query execution time, otherwise it will run native queries in unoptimized mode as SODA evaluations. On the Java platform the jars needed for native query optimization (db4o-X.x-nqopt.jar, bloat-X.x.jar) have to be on the classpath at runtime for this switch to have effect.

        The default setting is true.

        In client-server environment this setting should be used on both client and server.

        Parameters:
        optimizeNQ - true, if db4o should try to optimize native queries at query execution time, false otherwise

      • optimizeNativeQueries

        boolean optimizeNativeQueries()
        indicates whether Native Queries will be optimized dynamically.
        Returns:
        boolean true if Native Queries will be optimized dynamically.
        See Also:
        optimizeNativeQueries(boolean)

      • password

        void password​(java.lang.String pass)
       throws GlobalOnlyConfigException
        Deprecated.
        use a custom encrypting IoAdapter instead
        protects the database file with a password.

        To set a password for a database file, this method needs to be called before a database file is created with the first Db4o.openFile(java.lang.String).

        All further attempts to open the file, are required to set the same password.

        The password is used to seed the encryption mechanism, which makes it impossible to read the database file without knowing the password.

        Parameters:
        pass - the password to be used.
        Throws:
        GlobalOnlyConfigException

      • readOnly

        void readOnly​(boolean flag)
        turns readOnly mode on and off.

        This method configures the mode in which subsequent calls to Db4o.openFile() will open files.

        Readonly mode allows to open an unlimited number of reading processes on one database file. It is also convenient for deploying db4o database files on CD-ROM.

        In client-server environment this setting should be used on the server side in embedded mode and ONLY on client side in networked mode.

        Parameters:
        flag - true for configuring readOnly mode for subsequent calls to Db4o.openFile().

      • recoveryMode

        void recoveryMode​(boolean flag)
        turns recovery mode on and off.

        Recovery mode can be used to try to retrieve as much as possible out of an already corrupted database. In recovery mode internal checks are more relaxed. Null or invalid objects may be returned instead of throwing exceptions.

        Use this method with care as a last resort to get data out of a corrupted database.
        Parameters:
        flag - true to turn recover mode on.

      • reflectWith

        void reflectWith​(Reflector reflector)
        configures the use of a specially designed reflection implementation.

        db4o internally uses java.lang.reflect.* by default. On platforms that do not support this package, customized implementations may be written to supply all the functionality of the interfaces in the com.db4o.reflect package. This method can be used to install a custom reflection implementation.

        In client-server environment this setting should be used on the server side (reflector class must be available)

      • reserveStorageSpace

        void reserveStorageSpace​(long byteCount)
                  throws DatabaseReadOnlyException,
                         NotSupportedException
        tuning feature only: reserves a number of bytes in database files.

        The global setting is used for the creation of new database files. Continous calls on an ObjectContainer Configuration context (see ExtObjectContainer.configure()) will continually allocate space.

        The allocation of a fixed number of bytes at one time makes it more likely that the database will be stored in one chunk on the mass storage. Less read/write head movement can result in improved performance.

        Note:
        Allocated space will be lost on abnormal termination of the database engine (hardware crash, VM crash). A Defragment run will recover the lost space. For the best possible performance, this method should be called before the Defragment run to configure the allocation of storage space to be slightly greater than the anticipated database file size.

        In client-server environment this setting should be used on the server side.

        Default configuration: 0

        Parameters:
        byteCount - the number of bytes to reserve
        Throws:
        DatabaseReadOnlyException
        NotSupportedException

      • setBlobPath

        void setBlobPath​(java.lang.String path)
          throws java.io.IOException
        configures the path to be used to store and read Blob data.

        In client-server environment this setting should be used on the server side.

        Parameters:
        path - the path to be used
        Throws:
        java.io.IOException

      • setOut

        void setOut​(java.io.PrintStream outStream)
        Assigns a PrintStream where db4o is to print its event messages.

        Messages are useful for debugging purposes and for learning to understand, how db4o works. The message level can be raised with messageLevel(int) to produce more detailed messages.

        Use setOut(System.out) to print messages to the console.

        In client-server environment this setting should be used on the same side where messageLevel(int) is used.

        Parameters:
        outStream - the new PrintStream for messages.
        See Also:
        messageLevel(int)

      • stringEncoding

        void stringEncoding​(StringEncoding encoding)
        configures the string encoding to be used.

        The string encoding can not be changed in the lifetime of a database file. To set up the database with the correct string encoding, this configuration needs to be set correctly before a database file is created with the first call to Db4o.openFile(java.lang.String) or Db4o.openServer(java.lang.String, int).

        For subsequent open calls, db4o remembers built-in string encodings. If a custom encoding is used (an encoding that is not supplied from within the db4o library), the correct encoding needs to be configured correctly again for all subsequent calls that open database files.

        Example:
        config.stringEncoding(StringEncodings.utf8()));
        See Also:
        StringEncodings

      • testConstructors

        void testConstructors​(boolean flag)
        tuning feature: configures whether db4o should try to instantiate one instance of each persistent class on system startup.

        In a production environment this setting can be set to false, if all persistent classes have public default constructors.

        In client-server environment this setting should be used on both client and server side.

        Default value: true
        Parameters:
        flag - the desired setting

      • updateDepth

        void updateDepth​(int depth)
        specifies the global updateDepth.

        see the documentation of com.db4o.ObjectContainer#set for further details.

        The value be may be overridden for individual classes.

        The default setting is 1: Only the object passed to com.db4o.ObjectContainer#set will be updated.

        In client-server environment this setting should be used on both client and server sides.

        Parameters:
        depth - the depth of the desired update.
        See Also:
        ObjectClass.updateDepth(int), ObjectClass.cascadeOnUpdate(boolean), Using callbacks

      • weakReferences

        void weakReferences​(boolean flag)
        turns weak reference management on or off.

        This method must be called before opening a database.

        Performance may be improved by running db4o without using weak references durring memory management at the cost of higher memory consumption or by alternatively implementing a manual memory management scheme using ExtObjectContainer.purge(java.lang.Object)

        Setting the value to false causes db4o to use hard references to objects, preventing the garbage collection process from disposing of unused objects.

        The default setting is true.

      • weakReferenceCollectionInterval

        void weakReferenceCollectionInterval​(int milliseconds)
        configures the timer for WeakReference collection.

        The default setting is 1000 milliseconds.

        Configure this setting to zero to turn WeakReference collection off.
        Parameters:
        milliseconds - the time in milliseconds

      • registerTypeHandler

        void registerTypeHandler​(TypeHandlerPredicate predicate,
                         TypeHandler4 typeHandler)
        allows registering special TypeHandlers for customized marshalling and customized comparisons.
        Parameters:
        predicate - to specify for which classes and versions the TypeHandler is to be used.
        typeHandler - to be used for the classes that match the predicate.