org.apache.hadoop.hdfs.server.protocol

Interface JournalProtocol

All Known Implementing Classes:

JournalProtocolTranslatorPB

@InterfaceAudience.Private
public interface JournalProtocol

Protocol used to journal edits to a remote node. Currently, this is used to publish edits from the NameNode to a BackupNode.

Field Summary

Fields

Modifier and Type	Field and Description
static long	versionID This class is used by both the Namenode (client) and BackupNode (server) to insulate from the protocol serialization.

Method Summary

Methods

Modifier and Type	Method and Description
FenceResponse	fence(JournalInfo journalInfo, long epoch, String fencerInfo) Request to fence any other journal writers.
void	journal(JournalInfo journalInfo, long epoch, long firstTxnId, int numTxns, byte[] records) Journal edit records.
void	startLogSegment(JournalInfo journalInfo, long epoch, long txid) Notify the BackupNode that the NameNode has rolled its edit logs and is now writing a new log segment.

Field Detail

versionID

static final long versionID

This class is used by both the Namenode (client) and BackupNode (server) to insulate from the protocol serialization. If you are adding/changing DN's interface then you need to change both this class and ALSO related protocol buffer wire protocol definition in JournalProtocol.proto. For more details on protocol buffer wire protocol, please see .../org/apache/hadoop/hdfs/protocolPB/overview.html

See Also:

Constant Field Values

Method Detail

journal

void journal(JournalInfo journalInfo,
           long epoch,
           long firstTxnId,
           int numTxns,
           byte[] records)
             throws IOException

Journal edit records. This message is sent by the active name-node to the backup node via EditLogBackupOutputStream in order to synchronize meta-data changes with the backup namespace image.

Parameters:

journalInfo - journal information

epoch - marks beginning a new journal writer

firstTxnId - the first transaction of this batch

numTxns - number of transactions

records - byte array containing serialized journal records

Throws:

FencedException - if the resource has been fenced

IOException

startLogSegment

void startLogSegment(JournalInfo journalInfo,
                   long epoch,
                   long txid)
                     throws IOException

Notify the BackupNode that the NameNode has rolled its edit logs and is now writing a new log segment.

Parameters:

journalInfo - journal information

epoch - marks beginning a new journal writer

txid - the first txid in the new log

Throws:

FencedException - if the resource has been fenced

IOException

fence

FenceResponse fence(JournalInfo journalInfo,
                  long epoch,
                  String fencerInfo)
                    throws IOException

Request to fence any other journal writers. Older writers with at previous epoch will be fenced and can no longer perform journal operations.

Parameters:

journalInfo - journal information

epoch - marks beginning a new journal writer

fencerInfo - info about fencer for debugging purposes

Throws:

FencedException - if the resource has been fenced

IOException