Package org.apache.lucene.store

Class RAMDirectory

java.lang.Object

org.apache.lucene.store.Directory

org.apache.lucene.store.BaseDirectory

org.apache.lucene.store.RAMDirectory

All Implemented Interfaces:

Closeable, 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.

Nested Class Summary

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

Directory.IndexInputSlicer

Field Summary

Fields

Modifier and Type	Field	Description
protected Map<String,RAMFile>	fileMap
protected AtomicLong	sizeInBytes

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

isOpen, lockFactory

Constructor Summary

Constructors

Constructor	Description
RAMDirectory()	Constructs an empty Directory.
RAMDirectory(Directory dir, IOContext context)	Creates a new RAMDirectory instance from a different Directory implementation.

Method Summary

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

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

clearLock, ensureOpen, getLockFactory, makeLock, setLockFactory

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

copy, createSlicer, toString

Methods inherited from class java.lang.Object

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

Field Detail

fileMap

protected final Map<String,RAMFile> fileMap

sizeInBytes

protected final AtomicLong sizeInBytes

Constructor Detail

RAMDirectory

public RAMDirectory()

Constructs an empty Directory.

RAMDirectory

public RAMDirectory(Directory 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

Method Detail

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

listAll

public final 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(String name)

Returns true iff the named file exists in this directory.

Specified by:

fileExists in class Directory

fileLength

public final 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 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(String name)
                throws IOException

Removes an existing file in the directory.

Specified by:

deleteFile in class Directory

Throws:

IOException - if the file does not exist

createOutput

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

IOException

newRAMFile

protected RAMFile newRAMFile()

Returns a new RAMFile for storing data. This method can be overridden to return different RAMFile impls, that e.g. override RAMFile.newBuffer(int).

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

openInput

public IndexInput openInput(String name,
                            IOContext context)
                     throws IOException

Returns a stream reading an existing file.

Specified by:

openInput in class Directory

Throws:

IOException

close

public void close()

Closes the store to future operations, releasing associated memory.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Specified by:

close in class Directory