Class MMapDirectory
- java.lang.Object
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- org.apache.lucene.store.Directory
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- org.apache.lucene.store.FSDirectory
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- org.apache.lucene.store.MMapDirectory
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- All Implemented Interfaces:
Closeable
,AutoCloseable
public class MMapDirectory extends FSDirectory
File-basedDirectory
implementation that uses mmap for reading, andFSDirectory.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
istrue
, 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 aClosedChannelException
.
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Nested Class Summary
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Nested classes/interfaces inherited from class org.apache.lucene.store.FSDirectory
FSDirectory.FSIndexOutput
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Field Summary
Fields Modifier and Type Field Description 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
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Fields inherited from class org.apache.lucene.store.Directory
isOpen, lockFactory
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Constructor Summary
Constructors Constructor Description MMapDirectory(File path)
Create a new MMapDirectory for the named location andNativeFSLockFactory
.MMapDirectory(File path, LockFactory lockFactory)
Create a new MMapDirectory for the named location.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description int
getMaxChunkSize()
Returns the current mmap chunk size.boolean
getUseUnmap()
Returnstrue
, 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 1 GiBytes 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 closingIndexInput
, 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
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Methods inherited from class org.apache.lucene.store.Directory
clearLock, copy, copy, ensureOpen, getLockFactory, makeLock
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Constructor Detail
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MMapDirectory
public MMapDirectory(File path, LockFactory lockFactory) throws IOException
Create a new MMapDirectory for the named location.- Parameters:
path
- the path of the directorylockFactory
- the lock factory to use, or null for the default (NativeFSLockFactory
);- Throws:
IOException
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MMapDirectory
public MMapDirectory(File path) throws IOException
Create a new MMapDirectory for the named location andNativeFSLockFactory
.- Parameters:
path
- the path of the directory- Throws:
IOException
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Method Detail
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setUseUnmap
public void setUseUnmap(boolean useUnmapHack)
This method enables the workaround for unmapping the buffers from address space after closingIndexInput
, 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).- Throws:
IllegalArgumentException
- ifUNMAP_SUPPORTED
isfalse
and the workaround cannot be enabled.
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getUseUnmap
public boolean getUseUnmap()
Returnstrue
, if the unmap workaround is enabled.- See Also:
setUseUnmap(boolean)
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setMaxChunkSize
public final void setMaxChunkSize(int maxChunkSize)
Sets the maximum chunk size (default is 1 GiBytes 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 be1 << 30
, as the address space is big enough. Please note: This method always rounds down the chunk size to a power of 2.
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getMaxChunkSize
public final int getMaxChunkSize()
Returns the current mmap chunk size.- See Also:
setMaxChunkSize(int)
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openInput
public IndexInput openInput(String name, int bufferSize) throws IOException
Creates an IndexInput for the file with the given name.- Overrides:
openInput
in classDirectory
- Throws:
IOException
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