/**
* 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 org.apache.commons.io.IOUtils;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.fs.HFileSystem;
import com.google.common.annotations.VisibleForTesting;
/**
* 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 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 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 volatile int hbaseChecksumOffCount = -1;
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 {
this.stream.setDropBehind(dropBehind);
} catch (Exception e) {
// Skipped.
}
if (readahead >= 0) {
try {
this.stream.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. */
@VisibleForTesting
public FSDataInputStreamWrapper(FSDataInputStream fsdis) {
this(fsdis, fsdis);
}
/** For use in tests. */
@VisibleForTesting
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;
}
/**
* @return 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 = 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-- < 0)) {
// The stream we need is already open (because we were using HBase checksum in the past).
assert this.streamNoFsChecksum != null;
this.useHBaseChecksum = true;
}
}
/** Close stream(s) if necessary. */
@Override
public void close() {
if (!doCloseStreams) {
return;
}
// we do not care about the close exception as it is for reading, no data loss issue.
IOUtils.closeQuietly(streamNoFsChecksum);
IOUtils.closeQuietly(stream);
}
public HFileSystem getHfs() {
return this.hfs;
}
}