org.apache.lucene.store

Class FSDirectory

java.lang.Object

org.apache.lucene.store.Directory

org.apache.lucene.store.BaseDirectory

org.apache.lucene.store.FSDirectory

All Implemented Interfaces:

Closeable

Direct Known Subclasses:

MMapDirectory, NIOFSDirectory, SimpleFSDirectory

public abstract class FSDirectory
extends BaseDirectory

Base class for Directory implementations that store index files in the file system. There are currently three core subclasses:

• SimpleFSDirectory is a straightforward implementation using java.io.RandomAccessFile. However, it has poor concurrent performance (multiple threads will bottleneck) as it synchronizes when multiple threads read from the same file.
• NIOFSDirectory uses java.nio's FileChannel's positional io when reading to avoid synchronization when reading from the same file. Unfortunately, due to a Windows-only Sun JRE bug this is a poor choice for Windows, but on all other platforms this is the preferred choice. Applications using Thread.interrupt() or Future.cancel(boolean) should use SimpleFSDirectory instead. See NIOFSDirectory java doc for details.
• MMapDirectory uses memory-mapped IO when reading. This is a good choice if you have plenty of virtual memory relative to your index size, eg if you are running on a 64 bit JRE, or you are running on a 32 bit JRE but your index sizes are small enough to fit into the virtual memory space. Java has currently the limitation of not being able to unmap files from user code. The files are unmapped, when GC releases the byte buffers. 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 a (possibly dangerous) workaround mentioned in the bug report, which may fail on non-Sun JVMs. Applications using Thread.interrupt() or Future.cancel(boolean) should use SimpleFSDirectory instead. See MMapDirectory java doc for details.

Unfortunately, because of system peculiarities, there is no single overall best implementation. Therefore, we've added the open(java.io.File) method, to allow Lucene to choose the best FSDirectory implementation given your environment, and the known limitations of each implementation. For users who have no reason to prefer a specific implementation, it's best to simply use open(java.io.File). For all others, you should instantiate the desired implementation directly.

The locking implementation is by default NativeFSLockFactory, but can be changed by passing in a custom LockFactory instance.

See Also:

Directory

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected static class	FSDirectory.FSIndexInput Base class for reading input from a RandomAccessFile
protected static class	FSDirectory.FSIndexOutput Writes output with RandomAccessFile.write(byte[], int, int)

Nested classes/interfaces inherited from class org.apache.lucene.store.Directory

Directory.IndexInputSlicer

Field Summary

Fields

Modifier and Type	Field and Description
static int	DEFAULT_READ_CHUNK_SIZE Deprecated. This constant is no longer used since Lucene 4.5.
protected File	directory
protected Set<String>	staleFiles

Fields inherited from class org.apache.lucene.store.BaseDirectory

isOpen, lockFactory

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	FSDirectory(File path, LockFactory lockFactory) Create a new FSDirectory for the named location (ctor for subclasses).

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Closes the store to future operations.
IndexOutput	createOutput(String name, IOContext context) Creates an IndexOutput for the file with the given name.
void	deleteFile(String name) Removes an existing file in the directory.
protected void	ensureCanWrite(String name)
boolean	fileExists(String name) Returns true iff a file with the given name exists.
long	fileLength(String name) Returns the length in bytes of a file in the directory.
static long	fileModified(File directory, String name) Returns the time the named file was last modified.
protected void	fsync(String name)
File	getDirectory()
String	getLockID() Return a string identifier that uniquely differentiates this Directory instance from other Directory instances.
int	getReadChunkSize() Deprecated. This is no longer used since Lucene 4.5.
String[]	listAll() Lists all files (not subdirectories) in the directory.
static String[]	listAll(File dir) Lists all files (not subdirectories) in the directory.
protected void	onIndexOutputClosed(FSDirectory.FSIndexOutput io)
static FSDirectory	open(File path) Creates an FSDirectory instance, trying to pick the best implementation given the current environment.
static FSDirectory	open(File path, LockFactory lockFactory) Just like open(File), but allows you to also specify a custom LockFactory.
void	setLockFactory(LockFactory lockFactory) Set the LockFactory that this Directory instance should use for its locking implementation.
void	setReadChunkSize(int chunkSize) Deprecated. This is no longer used since Lucene 4.5.
void	sync(Collection<String> names) Ensure that any writes to these files are moved to stable storage.
String	toString() For debug output.

Methods inherited from class org.apache.lucene.store.BaseDirectory

clearLock, ensureOpen, getLockFactory, makeLock

Methods inherited from class org.apache.lucene.store.Directory

copy, createSlicer, openInput

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

DEFAULT_READ_CHUNK_SIZE

@Deprecated
public static final int DEFAULT_READ_CHUNK_SIZE

Deprecated. This constant is no longer used since Lucene 4.5.

Default read chunk size: 8192 bytes (this is the size up to which the JDK does not allocate additional arrays while reading/writing)

See Also:

Constant Field Values

directory

protected final File directory

staleFiles

protected final Set<String> staleFiles

Constructor Detail

FSDirectory

protected FSDirectory(File path,
           LockFactory lockFactory)
               throws IOException

Create a new FSDirectory for the named location (ctor for subclasses).

Parameters:

path - the path of the directory

lockFactory - the lock factory to use, or null for the default (NativeFSLockFactory);

Throws:

IOException - if there is a low-level I/O error

Method Detail

open

public static FSDirectory open(File path)
                        throws IOException

Creates an FSDirectory instance, trying to pick the best implementation given the current environment. The directory returned uses the NativeFSLockFactory.

Currently this returns MMapDirectory for most Solaris and Windows 64-bit JREs, NIOFSDirectory for other non-Windows JREs, and SimpleFSDirectory for other JREs on Windows. It is highly recommended that you consult the implementation's documentation for your platform before using this method.

NOTE: this method may suddenly change which implementation is returned from release to release, in the event that higher performance defaults become possible; if the precise implementation is important to your application, please instantiate it directly, instead. For optimal performance you should consider using MMapDirectory on 64 bit JVMs.

See above

Throws:

IOException

open

public static FSDirectory open(File path,
               LockFactory lockFactory)
                        throws IOException

Just like open(File), but allows you to also specify a custom LockFactory.

Throws:

IOException

setLockFactory

public void setLockFactory(LockFactory lockFactory)
                    throws IOException

Description copied from class: Directory

Set the LockFactory that this Directory instance should use for its locking implementation. Each * instance of LockFactory should only be used for one directory (ie, do not share a single instance across multiple Directories).

Overrides:

setLockFactory in class BaseDirectory

Parameters:

lockFactory - instance of LockFactory.

Throws:

IOException

listAll

public static String[] listAll(File dir)
                        throws IOException

Lists all files (not subdirectories) in the directory. This method never returns null (throws IOException instead).

Throws:

NoSuchDirectoryException - if the directory does not exist, or does exist but is not a directory.

IOException - if list() returns null

listAll

public String[] listAll()
                 throws IOException

Lists all files (not subdirectories) in the directory.

Specified by:

listAll in class Directory

Throws:

NoSuchDirectoryException - if the directory is not prepared for any write operations (such as Directory.createOutput(String, IOContext)).

IOException - in case of other IO errors

See Also:

listAll(File)

fileExists

public boolean fileExists(String name)

Returns true iff a file with the given name exists.

Specified by:

fileExists in class Directory

fileModified

public static long fileModified(File directory,
                String name)

Returns the time the named file was last modified.

fileLength

public 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 there was an IO error while retrieving the file's length.

deleteFile

public void deleteFile(String name)
                throws IOException

Removes an existing file in the directory.

Specified by:

deleteFile in class Directory

Throws:

IOException

createOutput

public IndexOutput createOutput(String name,
                       IOContext context)
                         throws IOException

Creates an IndexOutput for the file with the given name.

Specified by:

createOutput in class Directory

Throws:

IOException

ensureCanWrite

protected void ensureCanWrite(String name)
                       throws IOException

Throws:

IOException

onIndexOutputClosed

protected void onIndexOutputClosed(FSDirectory.FSIndexOutput io)

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

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

close

public void close()

Closes the store to future operations.

Specified by:

close in interface Closeable

Specified by:

close in class Directory

getDirectory

public File getDirectory()

Returns:

the underlying filesystem directory

toString

public String toString()

For debug output.

Overrides:

toString in class Directory

setReadChunkSize

@Deprecated
public final void setReadChunkSize(int chunkSize)

Deprecated. This is no longer used since Lucene 4.5.

This setting has no effect anymore.

getReadChunkSize

@Deprecated
public final int getReadChunkSize()

Deprecated. This is no longer used since Lucene 4.5.

This setting has no effect anymore.

fsync

protected void fsync(String name)
              throws IOException

Throws:

IOException