Package org.apache.lucene.store

Class RAMDirectory

  • All Implemented Interfaces:
    java.io.Closeable, java.lang.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.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void close()
      Closes the store to future operations, releasing associated memory.
      IndexOutput createOutput​(java.lang.String name, IOContext context)
      Creates a new, empty file in the directory with the given name.
      void deleteFile​(java.lang.String name)
      Removes an existing file in the directory.
      boolean fileExists​(java.lang.String name)
      Returns true iff the named file exists in this directory.
      long fileLength​(java.lang.String name)
      Returns the length in bytes of a file in the directory.
      java.lang.String getLockID()
      Return a string identifier that uniquely differentiates this Directory instance from other Directory instances.
      java.lang.String[] listAll()
      Returns an array of strings, one for each file in the directory.
      IndexInput openInput​(java.lang.String name, IOContext context)
      Returns a stream reading an existing file.
      long sizeInBytes()
      Return total size in bytes of all files in this directory.
      void sync​(java.util.Collection<java.lang.String> names)
      Ensure that any writes to these files are moved to stable storage.

      • Methods inherited from class java.lang.Object

        equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

    • Constructor Detail

      • RAMDirectory

        public RAMDirectory()
        Constructs an empty Directory.

      • RAMDirectory

        public RAMDirectory​(Directory dir,
                    IOContext context)
             throws java.io.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:
        java.io.IOException - if an error occurs

    • Method Detail

      • getLockID

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

      • fileLength

        public final long fileLength​(java.lang.String name)
                      throws java.io.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:
        java.io.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.

      • deleteFile

        public void deleteFile​(java.lang.String name)
                throws java.io.IOException
        Removes an existing file in the directory.
        Specified by:
        deleteFile in class Directory
        Throws:
        java.io.IOException - if the file does not exist

      • createOutput

        public IndexOutput createOutput​(java.lang.String name,
                                IOContext context)
                         throws java.io.IOException
        Creates a new, empty file in the directory with the given name. Returns a stream writing this file.
        Specified by:
        createOutput in class Directory
        Throws:
        java.io.IOException

      • sync

        public void sync​(java.util.Collection<java.lang.String> names)
          throws java.io.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:
        java.io.IOException

      • openInput

        public IndexInput openInput​(java.lang.String name,
                            IOContext context)
                     throws java.io.IOException
        Returns a stream reading an existing file.
        Specified by:
        openInput in class Directory
        Throws:
        java.io.IOException

      • close

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