Package org.apache.lucene.store

Class RAMDirectory

  • All Implemented Interfaces:
    Closeable, AutoCloseable
    public class RAMDirectory
extends BaseDirectory
    A memory-resident Directory implementation. Locking implementation is by default the SingleInstanceLockFactory but can be changed with BaseDirectory.setLockFactory(org.apache.lucene.store.LockFactory).

    Warning: This class is not intended to work with huge indexes. Everything beyond several hundred megabytes will waste resources (GC cycles), because it uses an internal buffer size of 1024 bytes, producing millions of byte[1024] arrays. This class is optimized for small memory-resident indexes. It also has bad concurrency on multithreaded environments.

    It is recommended to materialize large indexes on disk and use MMapDirectory, which is a high-performance directory implementation working directly on the file system cache of the operating system, so copying data to Java heap space is not useful.

    • Constructor Detail

      • RAMDirectory

        public RAMDirectory()
        Constructs an empty Directory.

      • RAMDirectory

        public RAMDirectory​(Directory dir,
                    IOContext context)
             throws IOException
        Creates a new RAMDirectory instance from a different Directory implementation. This can be used to load a disk-based index into memory.

        Warning: This class is not intended to work with huge indexes. Everything beyond several hundred megabytes will waste resources (GC cycles), because it uses an internal buffer size of 1024 bytes, producing millions of byte[1024] arrays. This class is optimized for small memory-resident indexes. It also has bad concurrency on multithreaded environments.

        For disk-based indexes it is recommended to use MMapDirectory, which is a high-performance directory implementation working directly on the file system cache of the operating system, so copying data to Java heap space is not useful.

        Note that the resulting RAMDirectory instance is fully independent from the original Directory (it is a complete copy). Any subsequent changes to the original Directory will not be visible in the RAMDirectory instance.

        Parameters:
        dir - a Directory value
        Throws:
        IOException - if an error occurs

    • Method Detail

      • getLockID

        public String getLockID()
        Description copied from class: Directory
        Return a string identifier that uniquely differentiates this Directory instance from other Directory instances. This ID should be the same if two Directory instances (even in different JVMs and/or on different machines) are considered "the same index". This is how locking "scopes" to the right index.
        Overrides:
        getLockID in class Directory

      • listAll

        public final String[] listAll()
        Description copied from class: Directory
        Returns an array of strings, one for each file in the directory.
        Specified by:
        listAll in class Directory

      • fileExists

        public final boolean fileExists​(String name)
        Returns true iff the named file exists in this directory.
        Specified by:
        fileExists in class Directory

      • fileLength

        public final long fileLength​(String name)
                      throws IOException
        Returns the length in bytes of a file in the directory.
        Specified by:
        fileLength in class Directory
        Parameters:
        name - the name of the file for which to return the length.
        Throws:
        IOException - if the file does not exist

      • sizeInBytes

        public final long sizeInBytes()
        Return total size in bytes of all files in this directory. This is currently quantized to RAMOutputStream.BUFFER_SIZE.

      • sync

        public void sync​(Collection<String> names)
          throws IOException
        Description copied from class: Directory
        Ensure that any writes to these files are moved to stable storage. Lucene uses this to properly commit changes to the index, to prevent a machine/OS crash from corrupting the index.

        NOTE: Clients may call this method for same files over and over again, so some impls might optimize for that. For other impls the operation can be a noop, for various reasons.
        Specified by:
        sync in class Directory
        Throws:
        IOException

      • close

        public void close()
        Closes the store to future operations, releasing associated memory.
        Specified by:
        close in interface AutoCloseable
        Specified by:
        close in interface Closeable
        Specified by:
        close in class Directory