/**
* 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.
*/
package org.apache.hadoop.hdfs;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.util.EnumSet;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.fs.ReadOption;
import org.apache.hadoop.hdfs.client.ClientMmap;
import org.apache.hadoop.hdfs.client.ShortCircuitReplica;
import org.apache.hadoop.hdfs.DFSClient.Conf;
import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
import org.apache.hadoop.hdfs.server.datanode.BlockMetadataHeader;
import org.apache.hadoop.hdfs.server.datanode.CachingStrategy;
import org.apache.hadoop.hdfs.util.DirectBufferPool;
import org.apache.hadoop.util.DataChecksum;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
/**
* BlockReaderLocal enables local short circuited reads. If the DFS client is on
* the same machine as the datanode, then the client can read files directly
* from the local file system rather than going through the datanode for better
* performance. <br>
* {@link BlockReaderLocal} works as follows:
* <ul>
* <li>The client performing short circuit reads must be configured at the
* datanode.</li>
* <li>The client gets the file descriptors for the metadata file and the data
* file for the block using
* {@link org.apache.hadoop.hdfs.server.datanode.DataXceiver#requestShortCircuitFds}.
* </li>
* <li>The client reads the file descriptors.</li>
* </ul>
*/
class BlockReaderLocal implements BlockReader {
static final Log LOG = LogFactory.getLog(BlockReaderLocal.class);
private static final DirectBufferPool bufferPool = new DirectBufferPool();
public static class Builder {
private final int bufferSize;
private boolean verifyChecksum;
private int maxReadahead;
private String filename;
private ShortCircuitReplica replica;
private long dataPos;
private ExtendedBlock block;
public Builder(Conf conf) {
this.maxReadahead = Integer.MAX_VALUE;
this.verifyChecksum = !conf.skipShortCircuitChecksums;
this.bufferSize = conf.shortCircuitBufferSize;
}
public Builder setVerifyChecksum(boolean verifyChecksum) {
this.verifyChecksum = verifyChecksum;
return this;
}
public Builder setCachingStrategy(CachingStrategy cachingStrategy) {
long readahead = cachingStrategy.getReadahead() != null ?
cachingStrategy.getReadahead() :
DFSConfigKeys.DFS_DATANODE_READAHEAD_BYTES_DEFAULT;
this.maxReadahead = (int)Math.min(Integer.MAX_VALUE, readahead);
return this;
}
public Builder setFilename(String filename) {
this.filename = filename;
return this;
}
public Builder setShortCircuitReplica(ShortCircuitReplica replica) {
this.replica = replica;
return this;
}
public Builder setStartOffset(long startOffset) {
this.dataPos = Math.max(0, startOffset);
return this;
}
public Builder setBlock(ExtendedBlock block) {
this.block = block;
return this;
}
public BlockReaderLocal build() {
Preconditions.checkNotNull(replica);
return new BlockReaderLocal(this);
}
}
private boolean closed = false;
/**
* Pair of streams for this block.
*/
private final ShortCircuitReplica replica;
/**
* The data FileChannel.
*/
private final FileChannel dataIn;
/**
* The next place we'll read from in the block data FileChannel.
*
* If data is buffered in dataBuf, this offset will be larger than the
* offset of the next byte which a read() operation will give us.
*/
private long dataPos;
/**
* The Checksum FileChannel.
*/
private final FileChannel checksumIn;
/**
* Checksum type and size.
*/
private final DataChecksum checksum;
/**
* If false, we will always skip the checksum.
*/
private final boolean verifyChecksum;
/**
* Name of the block, for logging purposes.
*/
private final String filename;
/**
* Block ID and Block Pool ID.
*/
private final ExtendedBlock block;
/**
* Cache of Checksum#bytesPerChecksum.
*/
private final int bytesPerChecksum;
/**
* Cache of Checksum#checksumSize.
*/
private final int checksumSize;
/**
* Maximum number of chunks to allocate.
*
* This is used to allocate dataBuf and checksumBuf, in the event that
* we need them.
*/
private final int maxAllocatedChunks;
/**
* True if zero readahead was requested.
*/
private final boolean zeroReadaheadRequested;
/**
* Maximum amount of readahead we'll do. This will always be at least the,
* size of a single chunk, even if {@link zeroReadaheadRequested} is true.
* The reason is because we need to do a certain amount of buffering in order
* to do checksumming.
*
* This determines how many bytes we'll use out of dataBuf and checksumBuf.
* Why do we allocate buffers, and then (potentially) only use part of them?
* The rationale is that allocating a lot of buffers of different sizes would
* make it very difficult for the DirectBufferPool to re-use buffers.
*/
private final int maxReadaheadLength;
/**
* Buffers data starting at the current dataPos and extending on
* for dataBuf.limit().
*
* This may be null if we don't need it.
*/
private ByteBuffer dataBuf;
/**
* Buffers checksums starting at the current checksumPos and extending on
* for checksumBuf.limit().
*
* This may be null if we don't need it.
*/
private ByteBuffer checksumBuf;
private BlockReaderLocal(Builder builder) {
this.replica = builder.replica;
this.dataIn = replica.getDataStream().getChannel();
this.dataPos = builder.dataPos;
this.checksumIn = replica.getMetaStream().getChannel();
BlockMetadataHeader header = builder.replica.getMetaHeader();
this.checksum = header.getChecksum();
this.verifyChecksum = builder.verifyChecksum &&
(this.checksum.getChecksumType().id != DataChecksum.CHECKSUM_NULL);
this.filename = builder.filename;
this.block = builder.block;
this.bytesPerChecksum = checksum.getBytesPerChecksum();
this.checksumSize = checksum.getChecksumSize();
this.maxAllocatedChunks = (bytesPerChecksum == 0) ? 0 :
((builder.bufferSize + bytesPerChecksum - 1) / bytesPerChecksum);
// Calculate the effective maximum readahead.
// We can't do more readahead than there is space in the buffer.
int maxReadaheadChunks = (bytesPerChecksum == 0) ? 0 :
((Math.min(builder.bufferSize, builder.maxReadahead) +
bytesPerChecksum - 1) / bytesPerChecksum);
if (maxReadaheadChunks == 0) {
this.zeroReadaheadRequested = true;
maxReadaheadChunks = 1;
} else {
this.zeroReadaheadRequested = false;
}
this.maxReadaheadLength = maxReadaheadChunks * bytesPerChecksum;
}
private synchronized void createDataBufIfNeeded() {
if (dataBuf == null) {
dataBuf = bufferPool.getBuffer(maxAllocatedChunks * bytesPerChecksum);
dataBuf.position(0);
dataBuf.limit(0);
}
}
private synchronized void freeDataBufIfExists() {
if (dataBuf != null) {
// When disposing of a dataBuf, we have to move our stored file index
// backwards.
dataPos -= dataBuf.remaining();
dataBuf.clear();
bufferPool.returnBuffer(dataBuf);
dataBuf = null;
}
}
private synchronized void createChecksumBufIfNeeded() {
if (checksumBuf == null) {
checksumBuf = bufferPool.getBuffer(maxAllocatedChunks * checksumSize);
checksumBuf.position(0);
checksumBuf.limit(0);
}
}
private synchronized void freeChecksumBufIfExists() {
if (checksumBuf != null) {
checksumBuf.clear();
bufferPool.returnBuffer(checksumBuf);
checksumBuf = null;
}
}
private synchronized int drainDataBuf(ByteBuffer buf)
throws IOException {
if (dataBuf == null) return -1;
int oldLimit = dataBuf.limit();
int nRead = Math.min(dataBuf.remaining(), buf.remaining());
if (nRead == 0) {
return (dataBuf.remaining() == 0) ? -1 : 0;
}
try {
dataBuf.limit(dataBuf.position() + nRead);
buf.put(dataBuf);
} finally {
dataBuf.limit(oldLimit);
}
return nRead;
}
/**
* Read from the block file into a buffer.
*
* This function overwrites checksumBuf. It will increment dataPos.
*
* @param buf The buffer to read into. May be dataBuf.
* The position and limit of this buffer should be set to
* multiples of the checksum size.
* @param canSkipChecksum True if we can skip checksumming.
*
* @return Total bytes read. 0 on EOF.
*/
private synchronized int fillBuffer(ByteBuffer buf, boolean canSkipChecksum)
throws IOException {
int total = 0;
long startDataPos = dataPos;
int startBufPos = buf.position();
while (buf.hasRemaining()) {
int nRead = dataIn.read(buf, dataPos);
if (nRead < 0) {
break;
}
dataPos += nRead;
total += nRead;
}
if (canSkipChecksum) {
freeChecksumBufIfExists();
return total;
}
if (total > 0) {
try {
buf.limit(buf.position());
buf.position(startBufPos);
createChecksumBufIfNeeded();
int checksumsNeeded = (total + bytesPerChecksum - 1) / bytesPerChecksum;
checksumBuf.clear();
checksumBuf.limit(checksumsNeeded * checksumSize);
long checksumPos =
7 + ((startDataPos / bytesPerChecksum) * checksumSize);
while (checksumBuf.hasRemaining()) {
int nRead = checksumIn.read(checksumBuf, checksumPos);
if (nRead < 0) {
throw new IOException("Got unexpected checksum file EOF at " +
checksumPos + ", block file position " + startDataPos + " for " +
"block " + block + " of file " + filename);
}
checksumPos += nRead;
}
checksumBuf.flip();
checksum.verifyChunkedSums(buf, checksumBuf, filename, startDataPos);
} finally {
buf.position(buf.limit());
}
}
return total;
}
private boolean createNoChecksumContext() {
if (verifyChecksum) {
return replica.addNoChecksumAnchor();
} else {
return true;
}
}
private void releaseNoChecksumContext() {
if (verifyChecksum) {
replica.removeNoChecksumAnchor();
}
}
@Override
public synchronized int read(ByteBuffer buf) throws IOException {
boolean canSkipChecksum = createNoChecksumContext();
try {
String traceString = null;
if (LOG.isTraceEnabled()) {
traceString = new StringBuilder().
append("read(").
append("buf.remaining=").append(buf.remaining()).
append(", block=").append(block).
append(", filename=").append(filename).
append(", canSkipChecksum=").append(canSkipChecksum).
append(")").toString();
LOG.info(traceString + ": starting");
}
int nRead;
try {
if (canSkipChecksum && zeroReadaheadRequested) {
nRead = readWithoutBounceBuffer(buf);
} else {
nRead = readWithBounceBuffer(buf, canSkipChecksum);
}
} catch (IOException e) {
if (LOG.isTraceEnabled()) {
LOG.info(traceString + ": I/O error", e);
}
throw e;
}
if (LOG.isTraceEnabled()) {
LOG.info(traceString + ": returning " + nRead);
}
return nRead;
} finally {
if (canSkipChecksum) releaseNoChecksumContext();
}
}
private synchronized int readWithoutBounceBuffer(ByteBuffer buf)
throws IOException {
freeDataBufIfExists();
freeChecksumBufIfExists();
int total = 0;
while (buf.hasRemaining()) {
int nRead = dataIn.read(buf, dataPos);
if (nRead <= 0) break;
dataPos += nRead;
total += nRead;
}
return (total == 0 && (dataPos == dataIn.size())) ? -1 : total;
}
/**
* Fill the data buffer. If necessary, validate the data against the
* checksums.
*
* We always want the offsets of the data contained in dataBuf to be
* aligned to the chunk boundary. If we are validating checksums, we
* accomplish this by seeking backwards in the file until we're on a
* chunk boundary. (This is necessary because we can't checksum a
* partial chunk.) If we are not validating checksums, we simply only
* fill the latter part of dataBuf.
*
* @param canSkipChecksum true if we can skip checksumming.
* @return true if we hit EOF.
* @throws IOException
*/
private synchronized boolean fillDataBuf(boolean canSkipChecksum)
throws IOException {
createDataBufIfNeeded();
final int slop = (int)(dataPos % bytesPerChecksum);
final long oldDataPos = dataPos;
dataBuf.limit(maxReadaheadLength);
if (canSkipChecksum) {
dataBuf.position(slop);
fillBuffer(dataBuf, canSkipChecksum);
} else {
dataPos -= slop;
dataBuf.position(0);
fillBuffer(dataBuf, canSkipChecksum);
}
dataBuf.limit(dataBuf.position());
dataBuf.position(Math.min(dataBuf.position(), slop));
if (LOG.isTraceEnabled()) {
LOG.trace("loaded " + dataBuf.remaining() + " bytes into bounce " +
"buffer from offset " + oldDataPos + " of " + block);
}
return dataBuf.limit() != maxReadaheadLength;
}
/**
* Read using the bounce buffer.
*
* A 'direct' read actually has three phases. The first drains any
* remaining bytes from the slow read buffer. After this the read is
* guaranteed to be on a checksum chunk boundary. If there are still bytes
* to read, the fast direct path is used for as many remaining bytes as
* possible, up to a multiple of the checksum chunk size. Finally, any
* 'odd' bytes remaining at the end of the read cause another slow read to
* be issued, which involves an extra copy.
*
* Every 'slow' read tries to fill the slow read buffer in one go for
* efficiency's sake. As described above, all non-checksum-chunk-aligned
* reads will be served from the slower read path.
*
* @param buf The buffer to read into.
* @param canSkipChecksum True if we can skip checksums.
*/
private synchronized int readWithBounceBuffer(ByteBuffer buf,
boolean canSkipChecksum) throws IOException {
int total = 0;
int bb = drainDataBuf(buf); // drain bounce buffer if possible
if (bb >= 0) {
total += bb;
if (buf.remaining() == 0) return total;
}
boolean eof = true, done = false;
do {
if (buf.isDirect() && (buf.remaining() >= maxReadaheadLength)
&& ((dataPos % bytesPerChecksum) == 0)) {
// Fast lane: try to read directly into user-supplied buffer, bypassing
// bounce buffer.
int oldLimit = buf.limit();
int nRead;
try {
buf.limit(buf.position() + maxReadaheadLength);
nRead = fillBuffer(buf, canSkipChecksum);
} finally {
buf.limit(oldLimit);
}
if (nRead < maxReadaheadLength) {
done = true;
}
if (nRead > 0) {
eof = false;
}
total += nRead;
} else {
// Slow lane: refill bounce buffer.
if (fillDataBuf(canSkipChecksum)) {
done = true;
}
bb = drainDataBuf(buf); // drain bounce buffer if possible
if (bb >= 0) {
eof = false;
total += bb;
}
}
} while ((!done) && (buf.remaining() > 0));
return (eof && total == 0) ? -1 : total;
}
@Override
public synchronized int read(byte[] arr, int off, int len)
throws IOException {
boolean canSkipChecksum = createNoChecksumContext();
int nRead;
try {
String traceString = null;
if (LOG.isTraceEnabled()) {
traceString = new StringBuilder().
append("read(arr.length=").append(arr.length).
append(", off=").append(off).
append(", len=").append(len).
append(", filename=").append(filename).
append(", block=").append(block).
append(", canSkipChecksum=").append(canSkipChecksum).
append(")").toString();
LOG.trace(traceString + ": starting");
}
try {
if (canSkipChecksum && zeroReadaheadRequested) {
nRead = readWithoutBounceBuffer(arr, off, len);
} else {
nRead = readWithBounceBuffer(arr, off, len, canSkipChecksum);
}
} catch (IOException e) {
if (LOG.isTraceEnabled()) {
LOG.trace(traceString + ": I/O error", e);
}
throw e;
}
if (LOG.isTraceEnabled()) {
LOG.trace(traceString + ": returning " + nRead);
}
} finally {
if (canSkipChecksum) releaseNoChecksumContext();
}
return nRead;
}
private synchronized int readWithoutBounceBuffer(byte arr[], int off,
int len) throws IOException {
freeDataBufIfExists();
freeChecksumBufIfExists();
int nRead = dataIn.read(ByteBuffer.wrap(arr, off, len), dataPos);
if (nRead > 0) {
dataPos += nRead;
} else if ((nRead == 0) && (dataPos == dataIn.size())) {
return -1;
}
return nRead;
}
private synchronized int readWithBounceBuffer(byte arr[], int off, int len,
boolean canSkipChecksum) throws IOException {
createDataBufIfNeeded();
if (!dataBuf.hasRemaining()) {
dataBuf.position(0);
dataBuf.limit(maxReadaheadLength);
fillDataBuf(canSkipChecksum);
}
if (dataBuf.remaining() == 0) return -1;
int toRead = Math.min(dataBuf.remaining(), len);
dataBuf.get(arr, off, toRead);
return toRead;
}
@Override
public synchronized long skip(long n) throws IOException {
int discardedFromBuf = 0;
long remaining = n;
if ((dataBuf != null) && dataBuf.hasRemaining()) {
discardedFromBuf = (int)Math.min(dataBuf.remaining(), n);
dataBuf.position(dataBuf.position() + discardedFromBuf);
remaining -= discardedFromBuf;
}
if (LOG.isTraceEnabled()) {
LOG.trace("skip(n=" + n + ", block=" + block + ", filename=" +
filename + "): discarded " + discardedFromBuf + " bytes from " +
"dataBuf and advanced dataPos by " + remaining);
}
dataPos += remaining;
return n;
}
@Override
public int available() throws IOException {
// We never do network I/O in BlockReaderLocal.
return Integer.MAX_VALUE;
}
@Override
public synchronized void close() throws IOException {
if (closed) return;
closed = true;
if (LOG.isTraceEnabled()) {
LOG.trace("close(filename=" + filename + ", block=" + block + ")");
}
replica.unref();
freeDataBufIfExists();
freeChecksumBufIfExists();
}
@Override
public synchronized void readFully(byte[] arr, int off, int len)
throws IOException {
BlockReaderUtil.readFully(this, arr, off, len);
}
@Override
public synchronized int readAll(byte[] buf, int off, int len)
throws IOException {
return BlockReaderUtil.readAll(this, buf, off, len);
}
@Override
public boolean isLocal() {
return true;
}
@Override
public boolean isShortCircuit() {
return true;
}
/**
* Get or create a memory map for this replica.
*
* There are two kinds of ClientMmap objects we could fetch here: one that
* will always read pre-checksummed data, and one that may read data that
* hasn't been checksummed.
*
* If we fetch the former, "safe" kind of ClientMmap, we have to increment
* the anchor count on the shared memory slot. This will tell the DataNode
* not to munlock the block until this ClientMmap is closed.
* If we fetch the latter, we don't bother with anchoring.
*
* @param opts The options to use, such as SKIP_CHECKSUMS.
*
* @return null on failure; the ClientMmap otherwise.
*/
@Override
public ClientMmap getClientMmap(EnumSet<ReadOption> opts) {
boolean anchor = verifyChecksum &&
(opts.contains(ReadOption.SKIP_CHECKSUMS) == false);
if (anchor) {
if (!createNoChecksumContext()) {
if (LOG.isTraceEnabled()) {
LOG.trace("can't get an mmap for " + block + " of " + filename +
" since SKIP_CHECKSUMS was not given, " +
"we aren't skipping checksums, and the block is not mlocked.");
}
return null;
}
}
ClientMmap clientMmap = null;
try {
clientMmap = replica.getOrCreateClientMmap(anchor);
} finally {
if ((clientMmap == null) && anchor) {
releaseNoChecksumContext();
}
}
return clientMmap;
}
@VisibleForTesting
boolean getVerifyChecksum() {
return this.verifyChecksum;
}
@VisibleForTesting
int getMaxReadaheadLength() {
return this.maxReadaheadLength;
}
/**
* Make the replica anchorable. Normally this can only be done by the
* DataNode. This method is only for testing.
*/
@VisibleForTesting
void forceAnchorable() {
replica.getSlot().makeAnchorable();
}
/**
* Make the replica unanchorable. Normally this can only be done by the
* DataNode. This method is only for testing.
*/
@VisibleForTesting
void forceUnanchorable() {
replica.getSlot().makeUnanchorable();
}
}