Class VFMemoryStorageFactory

java.lang.Object
org.apache.derby.impl.io.VFMemoryStorageFactory
All Implemented Interfaces:
StorageFactory, WritableStorageFactory
public class VFMemoryStorageFactory extends Object implements StorageFactory, WritableStorageFactory
A storage factory for virtual files, where the contents of the files are stored in main memory.

Note that data store deletion may happen inside one of two different methods; either in shutdown or in init. This is due to the current implementation and the fact that dropping a database is done through the file IO interface by deleting the service root. As the deletion then becomes a two step process, someone else may boot the database again before the reference to the store has been removed. To avoid this, the init-method will never initialize with a store scheduled for deletion. I have only seen this issue in heavily loaded multithreaded environments (2 CPUs/cores should be enough to reproduce).

  • Field Details

    • DATABASES

      private static final Map<String, DataStore> DATABASES
      References to the databases created / existing.

    • DUMMY_STORE

      private static final DataStore DUMMY_STORE
      Dummy store used to carry out frequent operations that don't require a "proper store", for instance getting the canonical name of the data store.

    • canonicalName

      private String canonicalName
      The canonical (unique) name of the database (absolute path).

    • dataDirectory

      private StorageFile dataDirectory
      The data directory of the database.

    • tempDir

      private StorageFile tempDir
      The temporary directory for the database (absolute path).

    • dbData

      private DataStore dbData
      The data store used for the database.

  • Constructor Details

    • VFMemoryStorageFactory

      public VFMemoryStorageFactory()
      Creates a new, uninitialized instance of the storage factory.

      To initialize the instance, init must be called.

      See Also:

  • Method Details

    • init

      public void init(String home, String databaseName, String tempDirNameIgnored, String uniqueName) throws IOException
      Initializes the storage factory instance by setting up a temporary directory, the database directory and checking if the database being named already exists.
      Specified by:
      init in interface StorageFactory
      Parameters:
      home - the value of system.home for this storage factory
      databaseName - the name of the database, all relative pathnames are relative to this name
      tempDirNameIgnored - ignored
      uniqueName - used to determine when the temporary directory can be created, but not to name the temporary directory itself
      Throws:
      IOException - on an error (unexpected).

    • shutdown

      public void shutdown()
      Normally does nothing, but if the database is in a state such that it should be deleted this will happen here.
      Specified by:
      shutdown in interface StorageFactory

    • getCanonicalName

      public String getCanonicalName()
      Description copied from interface: StorageFactory
      Get the canonical name of the database. This is a name that uniquely identifies it. It is system dependent. The normal, disk based implementation uses method java.io.File.getCanonicalPath on the directory holding the database to construct the canonical name.
      Specified by:
      getCanonicalName in interface StorageFactory
      Returns:
      the canonical name

    • setCanonicalName

      public void setCanonicalName(String name)
      Set the canonicalName. May need adjustment due to DERBY-5096
      Specified by:
      setCanonicalName in interface StorageFactory
      Parameters:
      name - uniquely identifiable name for this database

    • newStorageFile

      public StorageFile newStorageFile(String path)
      Returns a handle to the specific storage file.
      Specified by:
      newStorageFile in interface StorageFactory
      Parameters:
      path - the path of the file or directory
      Returns:
      A path handle.

    • newStorageFile

      public StorageFile newStorageFile(String directoryName, String fileName)
      Returns a handle to the specified storage file.
      Specified by:
      newStorageFile in interface StorageFactory
      Parameters:
      directoryName - the name of the parent directory
      fileName - the name of the file
      Returns:
      A path handle.

    • newStorageFile

      public StorageFile newStorageFile(StorageFile directoryName, String fileName)
      Returns a handle to the specified storage file.
      Specified by:
      newStorageFile in interface StorageFactory
      Parameters:
      directoryName - the name of the parent directory
      fileName - the name of the file
      Returns:
      A path handle.

    • getTempDir

      public StorageFile getTempDir()
      Returns the temporary directory for this storage factory instance.
      Specified by:
      getTempDir in interface StorageFactory
      Returns:
      A StorageFile-object representing the temp directory.

    • isFast

      public boolean isFast()
      The service is fast and supports random access.
      Specified by:
      isFast in interface StorageFactory
      Returns:
      true

    • isReadOnlyDatabase

      public boolean isReadOnlyDatabase()
      The service supports writes.
      Specified by:
      isReadOnlyDatabase in interface StorageFactory
      Returns:
      false

    • supportsRandomAccess

      public boolean supportsRandomAccess()
      The service supports random access.
      Specified by:
      supportsRandomAccess in interface StorageFactory
      Returns:
      true

    • getStorageFactoryVersion

      public int getStorageFactoryVersion()
      Specified by:
      getStorageFactoryVersion in interface StorageFactory
      Returns:
      the StorageFactory version supported by this implementation

    • createTemporaryFile

      public StorageFile createTemporaryFile(String prefix, String suffix)
      Creates a handle to a temporary file.
      Specified by:
      createTemporaryFile in interface StorageFactory
      Parameters:
      prefix - requested prefix for the file name
      suffix - requested suffix for the file name, if null then .tmp will be used
      Returns:
      A handle to the temporary file.

    • getSeparator

      public char getSeparator()
      Returns the path separator used by this storage factory.
      Specified by:
      getSeparator in interface StorageFactory
      Returns:
      PathUtil.SEP

    • sync

      public void sync(OutputStream stream, boolean metaData)
      The sync method is a no-op for this storage factory.
      Specified by:
      sync in interface WritableStorageFactory
      Parameters:
      stream - ignored
      metaData - ignored

    • supportsWriteSync

      public boolean supportsWriteSync()
      Description copied from interface: WritableStorageFactory
      This method tests whether the StorageRandomAccessFile "rws" and "rwd" modes are implemented. If the "rws" and "rwd" modes are supported then the database engine will conclude that the write methods of "rws"/"rwd" mode StorageRandomAccessFiles are slow but the sync method is fast and optimize accordingly.
      Specified by:
      supportsWriteSync in interface WritableStorageFactory
      Returns:
      true if an StIRandomAccess file opened with "rws" or "rwd" modes immediately writes data to the underlying storage, false if not.

    • normalizePath

      private String normalizePath(String dir, String file)
      Returns a normalized absolute path.
      Parameters:
      dir - parent directory, if null the dataDirectory will be used
      file - the file name (null not allowed)
      Returns:
      A path.
      Throws:
      NullPointerException - if file is null

    • normalizePath

      private String normalizePath(String path)
      Returns a normalized absolute path.
      Parameters:
      path - path, if null the dataDirectory will be used
      Returns:
      A path.

    • dbDropCleanupInDummy

      private void dbDropCleanupInDummy(String dbPath)
      Cleans up the internal dummy data store after a database has been dropped.
      Parameters:
      dbPath - absolute path of the dropped database