MMapDirectory

Class Overview

File-based Directory implementation that uses mmap for reading, and SimpleFSDirectory.SimpleFSIndexOutput 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 setMaxChunkSize(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 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 (disabled by default, see setUseUnmap(boolean)), 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.

Summary

[Expand] Inherited Fields
From class org.apache.lucene.store.FSDirectory public static final int DEFAULT_READ_CHUNK_SIZE Default read chunk size. protected File directory The underlying filesystem directory
From class org.apache.lucene.store.Directory protected boolean isOpen protected LockFactory lockFactory Holds the LockFactory instance (implements locking for this Directory instance).

[Expand] Inherited Methods
From class org.apache.lucene.store.FSDirectory synchronized void close() Closes the store to future operations. void deleteFile(String name) Removes an existing file in the directory. 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. long fileModified(String name) Returns the time the named file was last modified. static long fileModified(File directory, String name) Returns the time the named file was last modified. File getFile() String getLockID() Return a string identifier that uniquely differentiates this Directory instance from other Directory instances. final int getReadChunkSize() The maximum number of bytes to read at once from the underlying file during readBytes(byte[], int, int). final void initOutput(String name) Initializes the directory to create a new file with the given name. String[] listAll() Lists all files (not subdirectories) in the directory. static String[] listAll(File dir) Lists all files (not subdirectories) in the directory. static FSDirectory open(File path, LockFactory lockFactory) Just like open(File), but allows you to also specify a custom LockFactory. static FSDirectory open(File path) Creates an FSDirectory instance, trying to pick the best implementation given the current environment. IndexInput openInput(String name) Returns a stream reading an existing file. final void setReadChunkSize(int chunkSize) Sets the maximum number of bytes read at once from the underlying file during readBytes(byte[], int, int). void sync(String name) Ensure that any writes to this file are moved to stable storage. String toString() For debug output. void touchFile(String name) Set the modified time of an existing file to now.
From class org.apache.lucene.store.Directory void clearLock(String name) Attempt to clear (forcefully unlock and remove) the specified lock. abstract void close() Closes the store. static void copy(Directory src, Directory dest, boolean closeDirSrc) Copy contents of a directory src to a directory dest. abstract IndexOutput createOutput(String name) Creates a new, empty file in the directory with the given name. abstract void deleteFile(String name) Removes an existing file in the directory. final void ensureOpen() abstract boolean fileExists(String name) Returns true iff a file with the given name exists. abstract long fileLength(String name) Returns the length of a file in the directory. abstract long fileModified(String name) Returns the time the named file was last modified. LockFactory getLockFactory() Get the LockFactory that this Directory instance is using for its locking implementation. String getLockID() Return a string identifier that uniquely differentiates this Directory instance from other Directory instances. abstract String[] listAll() Returns an array of strings, one for each file in the directory. Lock makeLock(String name) Construct a Lock. IndexInput openInput(String name, int bufferSize) Returns a stream reading an existing file, with the specified read buffer size. abstract IndexInput openInput(String name) Returns a stream reading an existing file. void setLockFactory(LockFactory lockFactory) Set the LockFactory that this Directory instance should use for its locking implementation. void sync(String name) Ensure that any writes to this file are moved to stable storage. String toString() abstract void touchFile(String name) Set the modified time of an existing file to now.
From class java.lang.Object Object clone() boolean equals(Object arg0) void finalize() final Class<?> getClass() int hashCode() final void notify() final void notifyAll() String toString() final void wait() final void wait(long arg0, int arg1) final void wait(long arg0)
From interface java.io.Closeable abstract void close()