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Server functionality for HBase
/*
* 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.hbase.io;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.util.concurrent.atomic.AtomicInteger;
import org.apache.hadoop.fs.CanUnbuffer;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hbase.fs.HFileSystem;
import org.apache.hadoop.hdfs.client.HdfsDataInputStream;
import org.apache.yetus.audience.InterfaceAudience;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.hbase.thirdparty.com.google.common.io.Closeables;
/**
* Wrapper for input stream(s) that takes care of the interaction of FS and HBase checksums, as well
* as closing streams. Initialization is not thread-safe, but normal operation is; see method
* comments.
*/
@InterfaceAudience.Private
public class FSDataInputStreamWrapper implements Closeable {
private static final Logger LOG = LoggerFactory.getLogger(FSDataInputStreamWrapper.class);
private static final boolean isLogTraceEnabled = LOG.isTraceEnabled();
private final HFileSystem hfs;
private final Path path;
private final FileLink link;
private final boolean doCloseStreams;
private final boolean dropBehind;
private final long readahead;
/**
* Two stream handles, one with and one without FS-level checksum. HDFS checksum setting is on FS
* level, not single read level, so you have to keep two FS objects and two handles open to
* interleave different reads freely, which is very sad. This is what we do: 1) First, we need to
* read the trailer of HFile to determine checksum parameters. We always use FS checksum to do
* that, so ctor opens {@link #stream}. 2.1) After that, if HBase checksum is not used, we'd just
* always use {@link #stream}; 2.2) If HBase checksum can be used, we'll open
* {@link #streamNoFsChecksum}, and close {@link #stream}. User MUST call prepareForBlockReader
* for that to happen; if they don't, (2.1) will be the default. 3) The users can call
* {@link #shouldUseHBaseChecksum()}, and pass its result to {@link #getStream(boolean)} to get
* stream (if Java had out/pointer params we could return both in one call). This stream is
* guaranteed to be set. 4) The first time HBase checksum fails, one would call
* {@link #fallbackToFsChecksum(int)}. That will take lock, and open {@link #stream}. While this
* is going on, others will continue to use the old stream; if they also want to fall back,
* they'll also call {@link #fallbackToFsChecksum(int)}, and block until {@link #stream} is set.
* 5) After some number of checksumOk() calls, we will go back to using HBase checksum. We will
* have 2 handles; however we presume checksums fail so rarely that we don't care.
*/
private volatile FSDataInputStream stream = null;
private volatile FSDataInputStream streamNoFsChecksum = null;
private final Object streamNoFsChecksumFirstCreateLock = new Object();
// The configuration states that we should validate hbase checksums
private boolean useHBaseChecksumConfigured;
// Record the current state of this reader with respect to
// validating checkums in HBase. This is originally set the same
// value as useHBaseChecksumConfigured, but can change state as and when
// we encounter checksum verification failures.
private volatile boolean useHBaseChecksum;
// In the case of a checksum failure, do these many succeeding
// reads without hbase checksum verification.
private AtomicInteger hbaseChecksumOffCount = new AtomicInteger(-1);
private final static ReadStatistics readStatistics = new ReadStatistics();
private static class ReadStatistics {
long totalBytesRead;
long totalLocalBytesRead;
long totalShortCircuitBytesRead;
long totalZeroCopyBytesRead;
}
private Boolean instanceOfCanUnbuffer = null;
private CanUnbuffer unbuffer = null;
public FSDataInputStreamWrapper(FileSystem fs, Path path) throws IOException {
this(fs, path, false, -1L);
}
public FSDataInputStreamWrapper(FileSystem fs, Path path, boolean dropBehind, long readahead)
throws IOException {
this(fs, null, path, dropBehind, readahead);
}
public FSDataInputStreamWrapper(FileSystem fs, FileLink link, boolean dropBehind, long readahead)
throws IOException {
this(fs, link, null, dropBehind, readahead);
}
private FSDataInputStreamWrapper(FileSystem fs, FileLink link, Path path, boolean dropBehind,
long readahead) throws IOException {
assert (path == null) != (link == null);
this.path = path;
this.link = link;
this.doCloseStreams = true;
this.dropBehind = dropBehind;
this.readahead = readahead;
// If the fs is not an instance of HFileSystem, then create an instance of HFileSystem
// that wraps over the specified fs. In this case, we will not be able to avoid
// checksumming inside the filesystem.
this.hfs = (fs instanceof HFileSystem) ? (HFileSystem) fs : new HFileSystem(fs);
// Initially we are going to read the tail block. Open the reader w/FS checksum.
this.useHBaseChecksumConfigured = this.useHBaseChecksum = false;
this.stream = (link != null) ? link.open(hfs) : hfs.open(path);
setStreamOptions(stream);
}
private void setStreamOptions(FSDataInputStream in) {
try {
in.setDropBehind(dropBehind);
} catch (Exception e) {
// Skipped.
}
if (readahead >= 0) {
try {
in.setReadahead(readahead);
} catch (Exception e) {
// Skipped.
}
}
}
/**
* Prepares the streams for block reader. NOT THREAD SAFE. Must be called once, after any reads
* finish and before any other reads start (what happens in reality is we read the tail, then call
* this based on what's in the tail, then read blocks).
* @param forceNoHBaseChecksum Force not using HBase checksum.
*/
public void prepareForBlockReader(boolean forceNoHBaseChecksum) throws IOException {
if (hfs == null) return;
assert this.stream != null && !this.useHBaseChecksumConfigured;
boolean useHBaseChecksum =
!forceNoHBaseChecksum && hfs.useHBaseChecksum() && (hfs.getNoChecksumFs() != hfs);
if (useHBaseChecksum) {
FileSystem fsNc = hfs.getNoChecksumFs();
this.streamNoFsChecksum = (link != null) ? link.open(fsNc) : fsNc.open(path);
setStreamOptions(streamNoFsChecksum);
this.useHBaseChecksumConfigured = this.useHBaseChecksum = useHBaseChecksum;
// Close the checksum stream; we will reopen it if we get an HBase checksum failure.
this.stream.close();
this.stream = null;
}
}
/** For use in tests. */
public FSDataInputStreamWrapper(FSDataInputStream fsdis) {
this(fsdis, fsdis);
}
/** For use in tests. */
public FSDataInputStreamWrapper(FSDataInputStream fsdis, FSDataInputStream noChecksum) {
doCloseStreams = false;
stream = fsdis;
streamNoFsChecksum = noChecksum;
path = null;
link = null;
hfs = null;
useHBaseChecksumConfigured = useHBaseChecksum = false;
dropBehind = false;
readahead = 0;
}
/** Returns Whether we are presently using HBase checksum. */
public boolean shouldUseHBaseChecksum() {
return this.useHBaseChecksum;
}
/**
* Get the stream to use. Thread-safe.
* @param useHBaseChecksum must be the value that shouldUseHBaseChecksum has returned at some
* point in the past, otherwise the result is undefined.
*/
public FSDataInputStream getStream(boolean useHBaseChecksum) {
return useHBaseChecksum ? this.streamNoFsChecksum : this.stream;
}
/**
* Read from non-checksum stream failed, fall back to FS checksum. Thread-safe.
* @param offCount For how many checksumOk calls to turn off the HBase checksum.
*/
public FSDataInputStream fallbackToFsChecksum(int offCount) throws IOException {
// checksumOffCount is speculative, but let's try to reset it less.
boolean partOfConvoy = false;
if (this.stream == null) {
synchronized (streamNoFsChecksumFirstCreateLock) {
partOfConvoy = (this.stream != null);
if (!partOfConvoy) {
this.stream = (link != null) ? link.open(hfs) : hfs.open(path);
}
}
}
if (!partOfConvoy) {
this.useHBaseChecksum = false;
this.hbaseChecksumOffCount.set(offCount);
}
return this.stream;
}
/** Report that checksum was ok, so we may ponder going back to HBase checksum. */
public void checksumOk() {
if (
this.useHBaseChecksumConfigured && !this.useHBaseChecksum
&& (this.hbaseChecksumOffCount.getAndDecrement() < 0)
) {
// The stream we need is already open (because we were using HBase checksum in the past).
assert this.streamNoFsChecksum != null;
this.useHBaseChecksum = true;
}
}
private void updateInputStreamStatistics(FSDataInputStream stream) {
// If the underlying file system is HDFS, update read statistics upon close.
if (stream instanceof HdfsDataInputStream) {
/**
* Because HDFS ReadStatistics is calculated per input stream, it is not feasible to update
* the aggregated number in real time. Instead, the metrics are updated when an input stream
* is closed.
*/
HdfsDataInputStream hdfsDataInputStream = (HdfsDataInputStream) stream;
synchronized (readStatistics) {
readStatistics.totalBytesRead +=
hdfsDataInputStream.getReadStatistics().getTotalBytesRead();
readStatistics.totalLocalBytesRead +=
hdfsDataInputStream.getReadStatistics().getTotalLocalBytesRead();
readStatistics.totalShortCircuitBytesRead +=
hdfsDataInputStream.getReadStatistics().getTotalShortCircuitBytesRead();
readStatistics.totalZeroCopyBytesRead +=
hdfsDataInputStream.getReadStatistics().getTotalZeroCopyBytesRead();
}
}
}
public static long getTotalBytesRead() {
synchronized (readStatistics) {
return readStatistics.totalBytesRead;
}
}
public static long getLocalBytesRead() {
synchronized (readStatistics) {
return readStatistics.totalLocalBytesRead;
}
}
public static long getShortCircuitBytesRead() {
synchronized (readStatistics) {
return readStatistics.totalShortCircuitBytesRead;
}
}
public static long getZeroCopyBytesRead() {
synchronized (readStatistics) {
return readStatistics.totalZeroCopyBytesRead;
}
}
/** CloseClose stream(s) if necessary. */
@Override
public void close() {
if (!doCloseStreams) {
return;
}
updateInputStreamStatistics(this.streamNoFsChecksum);
// we do not care about the close exception as it is for reading, no data loss issue.
Closeables.closeQuietly(streamNoFsChecksum);
updateInputStreamStatistics(stream);
Closeables.closeQuietly(stream);
}
public HFileSystem getHfs() {
return this.hfs;
}
/**
* This will free sockets and file descriptors held by the stream only when the stream implements
* org.apache.hadoop.fs.CanUnbuffer. NOT THREAD SAFE. Must be called only when all the clients
* using this stream to read the blocks have finished reading. If by chance the stream is
* unbuffered and there are clients still holding this stream for read then on next client read
* request a new socket will be opened by Datanode without client knowing about it and will serve
* its read request. Note: If this socket is idle for some time then the DataNode will close the
* socket and the socket will move into CLOSE_WAIT state and on the next client request on this
* stream, the current socket will be closed and a new socket will be opened to serve the
* requests.
*/
@SuppressWarnings({ "rawtypes" })
public void unbuffer() {
FSDataInputStream stream = this.getStream(this.shouldUseHBaseChecksum());
if (stream != null) {
InputStream wrappedStream = stream.getWrappedStream();
// CanUnbuffer interface was added as part of HDFS-7694 and the fix is available in Hadoop
// 2.6.4+ and 2.7.1+ versions only so check whether the stream object implements the
// CanUnbuffer interface or not and based on that call the unbuffer api.
final Class streamClass = wrappedStream.getClass();
if (this.instanceOfCanUnbuffer == null) {
// To ensure we compute whether the stream is instance of CanUnbuffer only once.
this.instanceOfCanUnbuffer = false;
if (wrappedStream instanceof CanUnbuffer) {
this.unbuffer = (CanUnbuffer) wrappedStream;
this.instanceOfCanUnbuffer = true;
}
}
if (this.instanceOfCanUnbuffer) {
try {
this.unbuffer.unbuffer();
} catch (UnsupportedOperationException e) {
if (isLogTraceEnabled) {
LOG.trace("Failed to invoke 'unbuffer' method in class " + streamClass
+ " . So there may be the stream does not support unbuffering.", e);
}
}
} else {
if (isLogTraceEnabled) {
LOG.trace("Failed to find 'unbuffer' method in class " + streamClass);
}
}
}
}
}