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java.lang.Object org.apache.lucene.store.Directory org.apache.lucene.store.FSDirectory org.apache.lucene.store.MMapDirectory
public class MMapDirectory
File-based Directory
implementation that uses
mmap 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 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 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 the workaround mentioned in the bug report
(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
.
Nested Class Summary |
---|
Nested classes/interfaces inherited from class org.apache.lucene.store.FSDirectory |
---|
FSDirectory.FSIndexOutput |
Field Summary | |
---|---|
static int |
DEFAULT_MAX_BUFF
|
static boolean |
UNMAP_SUPPORTED
true , if this platform supports unmapping mmapped files. |
Fields inherited from class org.apache.lucene.store.FSDirectory |
---|
DEFAULT_READ_CHUNK_SIZE, directory, staleFiles |
Fields inherited from class org.apache.lucene.store.Directory |
---|
isOpen, lockFactory |
Constructor Summary | |
---|---|
MMapDirectory(File path)
Create a new MMapDirectory for the named location and NativeFSLockFactory . |
|
MMapDirectory(File path,
LockFactory lockFactory)
Create a new MMapDirectory for the named location. |
Method Summary | |
---|---|
int |
getMaxChunkSize()
Returns the current mmap chunk size. |
boolean |
getUseUnmap()
Returns true , if the unmap workaround is enabled. |
IndexInput |
openInput(String name,
int bufferSize)
Creates an IndexInput for the file with the given name. |
void |
setMaxChunkSize(int maxChunkSize)
Sets the maximum chunk size (default is Integer.MAX_VALUE for
64 bit JVMs and 256 MiBytes for 32 bit JVMs) used for memory mapping. |
void |
setUseUnmap(boolean useUnmapHack)
This method enables the workaround for unmapping the buffers from address space after closing IndexInput , that is
mentioned in the bug report. |
Methods inherited from class org.apache.lucene.store.FSDirectory |
---|
close, createOutput, deleteFile, ensureCanWrite, fileExists, fileLength, fileModified, fileModified, fsync, getDirectory, getFile, getLockID, getReadChunkSize, listAll, listAll, onIndexOutputClosed, open, open, openInput, setLockFactory, setReadChunkSize, sync, sync, toString, touchFile |
Methods inherited from class org.apache.lucene.store.Directory |
---|
clearLock, copy, copy, ensureOpen, getLockFactory, makeLock |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Field Detail |
---|
public static final int DEFAULT_MAX_BUFF
public static final boolean UNMAP_SUPPORTED
true
, if this platform supports unmapping mmapped files.
Constructor Detail |
---|
public MMapDirectory(File path, LockFactory lockFactory) throws IOException
path
- the path of the directorylockFactory
- the lock factory to use, or null for the default
(NativeFSLockFactory
);
IOException
public MMapDirectory(File path) throws IOException
NativeFSLockFactory
.
path
- the path of the directory
IOException
Method Detail |
---|
public void setUseUnmap(boolean useUnmapHack)
IndexInput
, that is
mentioned in the bug report. This hack may fail on non-Sun JVMs.
It forcefully unmaps the buffer on close by using
an undocumented internal cleanup functionality.
NOTE: Enabling this is completely unsupported
by Java and may lead to JVM crashes if IndexInput
is closed while another thread is still accessing it (SIGSEGV).
IllegalArgumentException
- if UNMAP_SUPPORTED
is false
and the workaround cannot be enabled.public boolean getUseUnmap()
true
, if the unmap workaround is enabled.
setUseUnmap(boolean)
public final void setMaxChunkSize(int maxChunkSize)
Integer.MAX_VALUE
for
64 bit JVMs and 256 MiBytes for 32 bit JVMs) 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
Java platforms, this parameter should always be 1 << 30
,
as the address space is big enough.
Please note: This method always rounds down the chunk size
to a power of 2.
public final int getMaxChunkSize()
setMaxChunkSize(int)
public IndexInput openInput(String name, int bufferSize) throws IOException
openInput
in class Directory
IOException
|
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