Class MMapDirectory

File-based Directory implementation that uses MemoryMappedFile for reading, and 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 runtime, or a 32 bit runtime with indexes that are guaranteed to fit within the address space. On 32 bit platforms also consult MMapDirectory(DirectoryInfo, 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.

NOTE: Unlike in Java, it is not recommended to use Interrupt() in .NET in conjunction with an open FSDirectory because it is not guaranteed to exit atomically. Any lock statement or Enter(object) call can throw a ThreadInterruptedException, which makes shutting down unpredictable. To exit parallel tasks safely, we recommend using Tasks and "interrupt" them with CancellationTokens.
Inheritance
object
Directory
BaseDirectory
FSDirectory
MMapDirectory
Implements
Inherited Members
Namespace: Lucene.Net.Store
Assembly: Lucene.Net.dll
Syntax
public class MMapDirectory : FSDirectory, IDisposable

Constructors

MMapDirectory(DirectoryInfo)

Create a new MMapDirectory for the named location and NativeFSLockFactory.

Declaration
public MMapDirectory(DirectoryInfo path)
Parameters
Type Name Description
DirectoryInfo path

the path of the directory
Exceptions
Type Condition
IOException

if there is a low-level I/O error

MMapDirectory(DirectoryInfo, LockFactory)

Create a new MMapDirectory for the named location.

Declaration
public MMapDirectory(DirectoryInfo path, LockFactory lockFactory)
Parameters
Type Name Description
DirectoryInfo path

the path of the directory
LockFactory lockFactory

the lock factory to use, or null for the default (NativeFSLockFactory);
Exceptions
Type Condition
IOException

if there is a low-level I/O error

MMapDirectory(DirectoryInfo, LockFactory, int)

Create a new MMapDirectory for the named location, specifying the maximum chunk size used for memory mapping.

Declaration
public MMapDirectory(DirectoryInfo path, LockFactory lockFactory, int maxChunkSize)
Parameters
Type Name Description
DirectoryInfo path

the path of the directory
LockFactory lockFactory

the lock factory to use, or null for the default (NativeFSLockFactory);
int maxChunkSize

maximum chunk size (default is 1 GiBytes for 64 bit runtimes and 256 MiBytes for 32 bit runtimes) 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 platforms, this parameter should always be 1 << 30, as the address space is big enough.

Please note: The chunk size is always rounded down to a power of 2.
Exceptions
Type Condition
IOException

if there is a low-level I/O error

MMapDirectory(string)

Create a new MMapDirectory for the named location and NativeFSLockFactory.

LUCENENET specific overload for convenience using string instead of DirectoryInfo.
Declaration
public MMapDirectory(string path)
Parameters
Type Name Description
string path

the path of the directory
Exceptions
Type Condition
IOException

if there is a low-level I/O error

MMapDirectory(string, LockFactory)

Create a new MMapDirectory for the named location.

LUCENENET specific overload for convenience using string instead of DirectoryInfo.
Declaration
public MMapDirectory(string path, LockFactory lockFactory)
Parameters
Type Name Description
string path

the path of the directory
LockFactory lockFactory

the lock factory to use, or null for the default (NativeFSLockFactory);
Exceptions
Type Condition
IOException

if there is a low-level I/O error

MMapDirectory(string, LockFactory, int)

Create a new MMapDirectory for the named location, specifying the maximum chunk size used for memory mapping.

LUCENENET specific overload for convenience using string instead of DirectoryInfo.
Declaration
public MMapDirectory(string path, LockFactory lockFactory, int maxChunkSize)
Parameters
Type Name Description
string path

the path of the directory
LockFactory lockFactory

the lock factory to use, or null for the default (NativeFSLockFactory);
int maxChunkSize

maximum chunk size (default is 1 GiBytes for 64 bit runtimes and 256 MiBytes for 32 bit runtimes) 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 platforms, this parameter should always be 1 << 30, as the address space is big enough.

Please note: The chunk size is always rounded down to a power of 2.
Exceptions
Type Condition
IOException

if there is a low-level I/O error

Fields

DEFAULT_MAX_BUFF

Default max chunk size.

Declaration
public static readonly int DEFAULT_MAX_BUFF
Field Value
Type Description
int
See Also

Properties

MaxChunkSize

Returns the current mmap chunk size.

Declaration
public int MaxChunkSize { get; }
Property Value
Type Description
int
See Also

Methods

CreateSlicer(string, IOContext)

Creates an Directory.IndexInputSlicer for the given file name. Directory.IndexInputSlicer allows other Directory implementations to efficiently open one or more sliced IndexInput instances from a single file handle. The underlying file handle is kept open until the Directory.IndexInputSlicer is closed.

Throws FileNotFoundException if the file does not exist.

Note

This API is for internal purposes only and might change in incompatible ways in the next release.

Note

This API is experimental and might change in incompatible ways in the next release.

Declaration
public override Directory.IndexInputSlicer CreateSlicer(string name, IOContext context)
Parameters
Type Name Description
string name
IOContext context
Returns
Type Description
Directory.IndexInputSlicer
Overrides
Exceptions
Type Condition
IOException

if an IOException occurs

OpenInput(string, IOContext)

Creates an IndexInput for the file with the given name.

Declaration
public override IndexInput OpenInput(string name, IOContext context)
Parameters
Type Name Description
string name
IOContext context
Returns
Type Description
IndexInput
Overrides

Implements