org.apache.lucene.store
Class RAMDirectory

java.lang.Object
  extended by org.apache.lucene.store.Directory
      extended by org.apache.lucene.store.RAMDirectory
All Implemented Interfaces:
Closeable

public class RAMDirectory
extends Directory

A memory-resident Directory implementation. Locking implementation is by default the SingleInstanceLockFactory but can be changed with Directory.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
protected  Map<String,RAMFile> fileMap
           
protected  AtomicLong sizeInBytes
           
 
Fields inherited from class org.apache.lucene.store.Directory
isOpen, lockFactory
 
Constructor Summary
RAMDirectory()
          Constructs an empty Directory.
RAMDirectory(Directory dir, IOContext context)
          Creates a new RAMDirectory instance from a different Directory implementation.
 
Method Summary
 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[] 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.Directory
clearLock, copy, createSlicer, ensureOpen, getLockFactory, getLockID, makeLock, setLockFactory, 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

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 Closeable
Specified by:
close in class Directory


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