org.apache.hadoop.hbase.regionserver.wal

Class ProtobufWALTailingReader

java.lang.Object

org.apache.hadoop.hbase.regionserver.wal.AbstractProtobufWALReader

org.apache.hadoop.hbase.regionserver.wal.ProtobufWALTailingReader

All Implemented Interfaces:

Closeable, AutoCloseable, AbstractFSWALProvider.Initializer, WALTailingReader

@InterfaceAudience.Private
public class ProtobufWALTailingReader
extends AbstractProtobufWALReader
implements WALTailingReader

A WAL reader for replication. It supports reset so can be used to tail a WAL file which is being written currently.

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.hadoop.hbase.wal.WALTailingReader

WALTailingReader.Result, WALTailingReader.State

Field Summary

Fields inherited from class org.apache.hadoop.hbase.regionserver.wal.AbstractProtobufWALReader

byteStringUncompressor, cellDecoder, codecClsName, compressionCtx, conf, decryptor, fileLength, fs, hasCompression, hasTagCompression, hasValueCompression, inputStream, path, PB_WAL_COMPLETE_MAGIC, PB_WAL_MAGIC, trailer, trailerPresent, trailerWarnSize, valueCompressionType, walEditsStopOffset

Constructor Summary

Constructors

Constructor and Description
ProtobufWALTailingReader()

Method Summary

Modifier and Type	Method and Description
protected InputStream	getCellCodecInputStream(org.apache.hadoop.fs.FSDataInputStream stream) Get or create the input stream used by cell decoder.
WALTailingReader.Result	next(long limit) Read the next entry and make sure the position after reading does not go beyond the given limit.
void	resetTo(long position, boolean resetCompression) Reopen the reader to see if there is new data arrives, and also seek(or skip) to the given position.
protected void	skipTo(long position) Skip to the given position.

Methods inherited from class org.apache.hadoop.hbase.regionserver.wal.AbstractProtobufWALReader

close, extractHiddenEof, getCodecClsName, getPosition, getPositionQuietly, getWriterClsNames, init, initWALCellCodec, isWALTrailer, open, reachWALEditsStopOffset, readHeader, readTrailer, trailerSize

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.apache.hadoop.hbase.wal.WALTailingReader

close, getPosition

Constructor Detail

ProtobufWALTailingReader

public ProtobufWALTailingReader()

Method Detail

next

public WALTailingReader.Result next(long limit)

Description copied from interface: WALTailingReader

Read the next entry and make sure the position after reading does not go beyond the given limit.

Notice that we will not throw any checked exception out, all the states are represented by the return value. Of course we will log the exceptions out. The reason why we do this is that, for tailing a WAL file which is currently being written, we will hit EOFException many times, so it should not be considered as an 'exception' and also, creating an Exception is a bit expensive.

Specified by:

next in interface WALTailingReader

Parameters:

limit - the position limit. See HBASE-14004 for more details about why we need this limitation. -1 means no limit.

resetTo

public void resetTo(long position,
                    boolean resetCompression)
             throws IOException

Description copied from interface: WALTailingReader

Reopen the reader to see if there is new data arrives, and also seek(or skip) to the given position.

If you want to read from the beginning instead of a given position, please pass -1 as position, then the reader will locate to the first entry. Notice that, since we have a magic header and a pb header, the first WAL entry is not located at position 0, so passing 0 will cause trouble.

Specified by:

resetTo in interface WALTailingReader

Parameters:

position - the position we want to start reading from after resetting, or -1 if you want to start reading from the beginning.

resetCompression - whether we also need to clear the compression context. If true, we will use skip instead of seek after resetting.

Throws:

IOException

getCellCodecInputStream

protected InputStream getCellCodecInputStream(org.apache.hadoop.fs.FSDataInputStream stream)

Description copied from class: AbstractProtobufWALReader

Get or create the input stream used by cell decoder.

For implementing replication, we may need to limit the bytes we can read, so here we provide a method so subclasses can wrap the original input stream.

Specified by:

getCellCodecInputStream in class AbstractProtobufWALReader

skipTo

protected void skipTo(long position)
               throws IOException

Description copied from class: AbstractProtobufWALReader

Skip to the given position.

Specified by:

skipTo in class AbstractProtobufWALReader

Throws:

IOException