org.apache.hadoop.hdfs.server.namenode

Class EditLogOutputStream

java.lang.Object

org.apache.hadoop.hdfs.server.namenode.EditLogOutputStream

All Implemented Interfaces:

Closeable, AutoCloseable

Direct Known Subclasses:

EditLogFileOutputStream

@InterfaceAudience.Private
@InterfaceStability.Evolving
public abstract class EditLogOutputStream
extends Object
implements Closeable

A generic abstract class to support journaling of edits logs into a persistent storage.

Constructor Summary

Constructors

Constructor and Description
EditLogOutputStream()

Method Summary

Methods

Modifier and Type	Method and Description
abstract void	abort() Close the stream without necessarily flushing any pending data.
abstract void	close() Close the journal.
abstract void	create() Create and initialize underlying persistent edits log storage.
void	flush() Flush data to persistent store.
void	flush(boolean durable)
protected abstract void	flushAndSync(boolean durable) Flush and sync all data that is ready to be flush setReadyToFlush() into underlying persistent store.
String	generateHtmlReport()
protected long	getNumSync() Return number of calls to #flushAndSync()
abstract void	setReadyToFlush() All data that has been written to the stream so far will be flushed.
boolean	shouldForceSync() Implement the policy when to automatically sync the buffered edits log The buffered edits can be flushed when the buffer becomes full or a certain period of time is elapsed.
abstract void	write(FSEditLogOp op) Write edits log operation to the stream.
abstract void	writeRaw(byte[] bytes, int offset, int length) Write raw data to an edit log.

Methods inherited from class java.lang.Object

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

Constructor Detail

EditLogOutputStream

public EditLogOutputStream()
                    throws IOException

Throws:

IOException

Method Detail

write

public abstract void write(FSEditLogOp op)
                    throws IOException

Write edits log operation to the stream.

Parameters:

op - operation

Throws:

IOException

writeRaw

public abstract void writeRaw(byte[] bytes,
            int offset,
            int length)
                       throws IOException

Write raw data to an edit log. This data should already have the transaction ID, checksum, etc included. It is for use within the BackupNode when replicating edits from the NameNode.

Parameters:

bytes - the bytes to write.

offset - offset in the bytes to write from

length - number of bytes to write

Throws:

IOException

create

public abstract void create()
                     throws IOException

Create and initialize underlying persistent edits log storage.

Throws:

IOException

close

public abstract void close()
                    throws IOException

Close the journal.

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Throws:

IOException - if the journal can't be closed, or if there are unflushed edits

abort

public abstract void abort()
                    throws IOException

Close the stream without necessarily flushing any pending data. This may be called after a previous write or close threw an exception.

Throws:

IOException

setReadyToFlush

public abstract void setReadyToFlush()
                              throws IOException

All data that has been written to the stream so far will be flushed. New data can be still written to the stream while flushing is performed.

Throws:

IOException

flushAndSync

protected abstract void flushAndSync(boolean durable)
                              throws IOException

Flush and sync all data that is ready to be flush setReadyToFlush() into underlying persistent store.

Parameters:

durable - if true, the edits should be made truly durable before returning

Throws:

IOException

flush

public void flush()
           throws IOException

Flush data to persistent store. Collect sync metrics.

Throws:

IOException

flush

public void flush(boolean durable)
           throws IOException

Throws:

IOException

shouldForceSync

public boolean shouldForceSync()

Implement the policy when to automatically sync the buffered edits log The buffered edits can be flushed when the buffer becomes full or a certain period of time is elapsed.

Returns:

true if the buffered data should be automatically synced to disk

getNumSync

protected long getNumSync()

Return number of calls to #flushAndSync()

generateHtmlReport

public String generateHtmlReport()

Returns:

a short HTML snippet suitable for describing the current status of the stream