org.apache.lucene.store

Class RAMDirectory

  • All Implemented Interfaces:
    Closeable, AutoCloseable, Accountable


    public class RAMDirectory
    extends BaseDirectory
    implements Accountable
    A memory-resident Directory implementation. Locking implementation is by default the SingleInstanceLockFactory.

    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(FSDirectory 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