C# Class Lucene.Net.Store.MMapDirectory

File-based Directory implementation that uses mmap for reading, and {@link FSDirectory.FSIndexOutput} for writing.

NOTE: memory mapping uses up a portion of the virtual memory address space in your process equal to the size of the file being mapped. Before using this class, be sure your have plenty of virtual address space, e.g. by using a 64 bit JRE, or a 32 bit JRE with indexes that are guaranteed to fit within the address space. On 32 bit platforms also consult #MMapDirectory(File, LockFactory, int) if you have problems with mmap failing because of fragmented address space. If you get an OutOfMemoryException, it is recommended to reduce the chunk size, until it works.

Due to this bug in Sun's JRE, MMapDirectory's IndexInput#close is unable to close the underlying OS file handle. Only when GC finally collects the underlying objects, which could be quite some time later, will the file handle be closed.

this will consume additional transient disk usage: on Windows, attempts to delete or overwrite the files will result in an exception; on other platforms, which typically have a "delete on last close" semantics, while such operations will succeed, the bytes are still consuming space on disk. For many applications this limitation is not a problem (e.g. if you have plenty of disk space, and you don't rely on overwriting files on Windows) but it's still an important limitation to be aware of.

this class supplies the workaround mentioned in the bug report (see #setUseUnmap), which may fail on non-Sun JVMs. It forcefully unmaps the buffer on close by using an undocumented internal cleanup functionality. #UNMAP_SUPPORTED is true, if the workaround can be enabled (with no guarantees).

NOTE: Accessing this class either directly or indirectly from a thread while it's interrupted can close the underlying channel immediately if at the same time the thread is blocked on IO. The channel will remain closed and subsequent access to MMapDirectory will throw a ClosedChannelException.

Inheritance: FSDirectory
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Public Properties

Property Type Description
DEFAULT_MAX_BUFF int
UNMAP_SUPPORTED bool

Public Methods

Method Description
CreateSlicer ( string name, IOContext context ) : IndexInputSlicer
MMapDirectory ( DirectoryInfo path ) : System

Create a new MMapDirectory for the named location and NativeFSLockFactory.
MMapDirectory ( DirectoryInfo path, Lucene.Net.Store.LockFactory lockFactory ) : System

Create a new MMapDirectory for the named location.
MMapDirectory ( DirectoryInfo path, Lucene.Net.Store.LockFactory lockFactory, int maxChunkSize ) : System

Create a new MMapDirectory for the named location, specifying the maximum chunk size used for memory mapping.
OpenInput ( string name, IOContext context ) : IndexInput

Creates an IndexInput for the file with the given name.

Private Methods

Method Description
Map ( MMapIndexInput input, FileStream fc, long offset, long length ) : System.ByteBuffer[]

Maps a file into a set of buffers

Method Details

CreateSlicer() public method

public CreateSlicer ( string name, IOContext context ) : IndexInputSlicer
name string
context IOContext
return IndexInputSlicer

MMapDirectory() public method

Create a new MMapDirectory for the named location and NativeFSLockFactory.
if there is a low-level I/O error
public MMapDirectory ( DirectoryInfo path ) : System
path System.IO.DirectoryInfo the path of the directory
return System

MMapDirectory() public method

Create a new MMapDirectory for the named location.
if there is a low-level I/O error
public MMapDirectory ( DirectoryInfo path, Lucene.Net.Store.LockFactory lockFactory ) : System
path System.IO.DirectoryInfo the path of the directory
lockFactory Lucene.Net.Store.LockFactory the lock factory to use, or null for the default /// ();
return System

MMapDirectory() public method

Create a new MMapDirectory for the named location, specifying the maximum chunk size used for memory mapping.
if there is a low-level I/O error
public MMapDirectory ( DirectoryInfo path, Lucene.Net.Store.LockFactory lockFactory, int maxChunkSize ) : System
path System.IO.DirectoryInfo the path of the directory
lockFactory Lucene.Net.Store.LockFactory the lock factory to use, or null for the default /// ();
maxChunkSize int maximum chunk size (default is 1 GiBytes for /// 64 bit JVMs and 256 MiBytes for 32 bit JVMs) used for memory mapping. ///

/// Especially on 32 bit platform, the address space can be very fragmented, /// so large index files cannot be mapped. Using a lower chunk size makes /// the directory implementation a little bit slower (as the correct chunk /// may be resolved on lots of seeks) but the chance is higher that mmap /// does not fail. On 64 bit Java platforms, this parameter should always /// be {@code 1 << 30}, as the address space is big enough. ///

/// Please note: The chunk size is always rounded down to a power of 2.

return System

OpenInput() public method

Creates an IndexInput for the file with the given name.
public OpenInput ( string name, IOContext context ) : IndexInput
name string
context IOContext
return IndexInput

Property Details

DEFAULT_MAX_BUFF public_oe static_oe property

Default max chunk size.
public static int DEFAULT_MAX_BUFF
return int

UNMAP_SUPPORTED public_oe static_oe property

true, if this platform supports unmapping mmapped files.
public static bool UNMAP_SUPPORTED
return bool