package org.apache.lucene.store;
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import java.io.IOException;
import java.io.File;
import java.nio.ByteBuffer;
import java.nio.channels.ClosedChannelException; // javadoc @link
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;
import java.nio.file.StandardOpenOption;
import java.security.AccessController;
import java.security.PrivilegedExceptionAction;
import java.security.PrivilegedActionException;
import java.util.Locale;
import java.lang.reflect.Method;
import org.apache.lucene.store.ByteBufferIndexInput.BufferCleaner;
import org.apache.lucene.util.Constants;
/** File-based {@link Directory} implementation that uses
* mmap for reading, and {@link
* FSDirectory.FSIndexOutput} for writing.
*
* <p><b>NOTE</b>: 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 {@link #MMapDirectory(File, LockFactory, 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.
*
* <p>Due to <a href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4724038">
* this bug</a> in Sun's JRE, MMapDirectory's {@link 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.
*
* <p>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.
*
* <p>This class supplies the workaround mentioned in the bug report
* (see {@link #setUseUnmap}), which may fail on
* non-Sun JVMs. It forcefully unmaps the buffer on close by using
* an undocumented internal cleanup functionality.
* {@link #UNMAP_SUPPORTED} is <code>true</code>, if the workaround
* can be enabled (with no guarantees).
* <p>
* <b>NOTE:</b> 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 {@link MMapDirectory} will throw a {@link ClosedChannelException}.
* </p>
* @see <a href="http://blog.thetaphi.de/2012/07/use-lucenes-mmapdirectory-on-64bit.html">Blog post about MMapDirectory</a>
*/
public class MMapDirectory extends FSDirectory {
private boolean useUnmapHack = UNMAP_SUPPORTED;
/**
* Default max chunk size.
* @see #MMapDirectory(File, LockFactory, int)
*/
public static final int DEFAULT_MAX_BUFF = Constants.JRE_IS_64BIT ? (1 << 30) : (1 << 28);
final int chunkSizePower;
/** Create a new MMapDirectory for the named location.
*
* @param path the path of the directory
* @param lockFactory the lock factory to use, or null for the default
* ({@link NativeFSLockFactory});
* @throws IOException if there is a low-level I/O error
*/
public MMapDirectory(File path, LockFactory lockFactory) throws IOException {
this(path, lockFactory, DEFAULT_MAX_BUFF);
}
/** Create a new MMapDirectory for the named location and {@link NativeFSLockFactory}.
*
* @param path the path of the directory
* @throws IOException if there is a low-level I/O error
*/
public MMapDirectory(File path) throws IOException {
this(path, null);
}
/**
* Create a new MMapDirectory for the named location, specifying the
* maximum chunk size used for memory mapping.
*
* @param path the path of the directory
* @param lockFactory the lock factory to use, or null for the default
* ({@link NativeFSLockFactory});
* @param maxChunkSize maximum chunk size (default is 1 GiBytes for
* 64 bit JVMs and 256 MiBytes for 32 bit JVMs) used for memory mapping.
* <p>
* 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 {@code 1 << 30}, as the address space is big enough.
* <p>
* <b>Please note:</b> The chunk size is always rounded down to a power of 2.
* @throws IOException if there is a low-level I/O error
*/
public MMapDirectory(File path, LockFactory lockFactory, int maxChunkSize) throws IOException {
super(path, lockFactory);
if (maxChunkSize <= 0) {
throw new IllegalArgumentException("Maximum chunk size for mmap must be >0");
}
this.chunkSizePower = 31 - Integer.numberOfLeadingZeros(maxChunkSize);
assert this.chunkSizePower >= 0 && this.chunkSizePower <= 30;
}
/**
* <code>true</code>, if this platform supports unmapping mmapped files.
*/
public static final boolean UNMAP_SUPPORTED;
static {
boolean v;
try {
Class.forName("sun.misc.Cleaner");
Class.forName("java.nio.DirectByteBuffer")
.getMethod("cleaner");
v = true;
} catch (Exception e) {
v = false;
}
UNMAP_SUPPORTED = v;
}
/**
* This method enables the workaround for unmapping the buffers
* from address space after closing {@link 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.
* <p><b>NOTE:</b> Enabling this is completely unsupported
* by Java and may lead to JVM crashes if <code>IndexInput</code>
* is closed while another thread is still accessing it (SIGSEGV).
* @throws IllegalArgumentException if {@link #UNMAP_SUPPORTED}
* is <code>false</code> and the workaround cannot be enabled.
*/
public void setUseUnmap(final boolean useUnmapHack) {
if (useUnmapHack && !UNMAP_SUPPORTED)
throw new IllegalArgumentException("Unmap hack not supported on this platform!");
this.useUnmapHack=useUnmapHack;
}
/**
* Returns <code>true</code>, if the unmap workaround is enabled.
* @see #setUseUnmap
*/
public boolean getUseUnmap() {
return useUnmapHack;
}
/**
* Returns the current mmap chunk size.
* @see #MMapDirectory(File, LockFactory, int)
*/
public final int getMaxChunkSize() {
return 1 << chunkSizePower;
}
/** Creates an IndexInput for the file with the given name. */
@Override
public IndexInput openInput(String name, IOContext context) throws IOException {
ensureOpen();
File file = new File(getDirectory(), name);
try (FileChannel c = FileChannel.open(file.toPath(), StandardOpenOption.READ)) {
final String resourceDescription = "MMapIndexInput(path=\"" + file.toString() + "\")";
final boolean useUnmap = getUseUnmap();
return ByteBufferIndexInput.newInstance(resourceDescription,
map(resourceDescription, c, 0, c.size()),
c.size(), chunkSizePower, useUnmap ? CLEANER : null, useUnmap);
}
}
/** Maps a file into a set of buffers */
final ByteBuffer[] map(String resourceDescription, FileChannel fc, long offset, long length) throws IOException {
if ((length >>> chunkSizePower) >= Integer.MAX_VALUE)
throw new IllegalArgumentException("RandomAccessFile too big for chunk size: " + resourceDescription);
final long chunkSize = 1L << chunkSizePower;
// we always allocate one more buffer, the last one may be a 0 byte one
final int nrBuffers = (int) (length >>> chunkSizePower) + 1;
ByteBuffer buffers[] = new ByteBuffer[nrBuffers];
long bufferStart = 0L;
for (int bufNr = 0; bufNr < nrBuffers; bufNr++) {
int bufSize = (int) ( (length > (bufferStart + chunkSize))
? chunkSize
: (length - bufferStart)
);
try {
buffers[bufNr] = fc.map(MapMode.READ_ONLY, offset + bufferStart, bufSize);
} catch (IOException ioe) {
throw convertMapFailedIOException(ioe, resourceDescription, bufSize);
}
bufferStart += bufSize;
}
return buffers;
}
private IOException convertMapFailedIOException(IOException ioe, String resourceDescription, int bufSize) {
final String originalMessage;
final Throwable originalCause;
if (ioe.getCause() instanceof OutOfMemoryError) {
// nested OOM confuses users, because its "incorrect", just print a plain message:
originalMessage = "Map failed";
originalCause = null;
} else {
originalMessage = ioe.getMessage();
originalCause = ioe.getCause();
}
final String moreInfo;
if (!Constants.JRE_IS_64BIT) {
moreInfo = "MMapDirectory should only be used on 64bit platforms, because the address space on 32bit operating systems is too small. ";
} else if (Constants.WINDOWS) {
moreInfo = "Windows is unfortunately very limited on virtual address space. If your index size is several hundred Gigabytes, consider changing to Linux. ";
} else if (Constants.LINUX) {
moreInfo = "Please review 'ulimit -v', 'ulimit -m' (both should return 'unlimited'), and 'sysctl vm.max_map_count'. ";
} else {
moreInfo = "Please review 'ulimit -v', 'ulimit -m' (both should return 'unlimited'). ";
}
final IOException newIoe = new IOException(String.format(Locale.ENGLISH,
"%s: %s [this may be caused by lack of enough unfragmented virtual address space "+
"or too restrictive virtual memory limits enforced by the operating system, "+
"preventing us to map a chunk of %d bytes. %sMore information: "+
"http://blog.thetaphi.de/2012/07/use-lucenes-mmapdirectory-on-64bit.html]",
originalMessage, resourceDescription, bufSize, moreInfo), originalCause);
newIoe.setStackTrace(ioe.getStackTrace());
return newIoe;
}
private static final BufferCleaner CLEANER = new BufferCleaner() {
@Override
public void freeBuffer(final ByteBufferIndexInput parent, final ByteBuffer buffer) throws IOException {
try {
AccessController.doPrivileged(new PrivilegedExceptionAction<Void>() {
@Override
public Void run() throws Exception {
final Method getCleanerMethod = buffer.getClass()
.getMethod("cleaner");
getCleanerMethod.setAccessible(true);
final Object cleaner = getCleanerMethod.invoke(buffer);
if (cleaner != null) {
cleaner.getClass().getMethod("clean")
.invoke(cleaner);
}
return null;
}
});
} catch (PrivilegedActionException e) {
throw new IOException("Unable to unmap the mapped buffer: " + parent.toString(), e.getCause());
}
}
};
}