alluxio.master.journalv0

Interface JournalWriter

All Known Implementing Classes:

UfsJournalWriter

public interface JournalWriter

This class manages all the writes to the journal. Journal writes happen in two phases: 1. First the checkpoint is written. The checkpoint contains entries reflecting the state of the master with all of the completed logs applied. 2. Afterwards, entries are appended to log. The checkpoint must be written before the logs. The latest state can be reconstructed by reading the checkpoint, and applying all the completed logs and finally the current log.

Method Summary

Modifier and Type	Method and Description
void	close() Closes the journal.
void	completeCurrentLog() Marks the current log as completed.
void	completeLogs() Marks all logs as completed.
void	deleteCompletedLogs() Deletes all of the completed logs.
void	flush() Flushes the current log stream.
JournalOutputStream	getCheckpointOutputStream(long latestSequenceNumber) Returns an output stream for the journal checkpoint.
long	getNextSequenceNumber()
void	recover() Recovers the checkpoint in case the master crashed while updating it previously.
void	write(Journal.JournalEntry entry) Writes an entry to the current log stream.

Method Detail

completeLogs

void completeLogs()
           throws IOException

Marks all logs as completed.

Throws:

IOException

getCheckpointOutputStream

JournalOutputStream getCheckpointOutputStream(long latestSequenceNumber)
                                       throws IOException

Returns an output stream for the journal checkpoint. The returned output stream is a singleton for this writer.

Parameters:

latestSequenceNumber - the sequence number of the latest journal entry. This sequence number will be used to determine the next sequence numbers for the subsequent journal entries.

Returns:

the output stream for the journal checkpoint

Throws:

IOException

write

void write(Journal.JournalEntry entry)
    throws IOException

Writes an entry to the current log stream. flush() should be called afterward to ensure the entry is persisted.

Parameters:

entry - the journal entry to write

Throws:

IOException

flush

void flush()
    throws IOException

Flushes the current log stream. Otherwise this operation is a no-op.

Throws:

IOException

getNextSequenceNumber

long getNextSequenceNumber()

Returns:

the next sequence number

close

void close()
    throws IOException

Closes the journal.

Throws:

IOException

recover

void recover()

Recovers the checkpoint in case the master crashed while updating it previously.

deleteCompletedLogs

void deleteCompletedLogs()
                  throws IOException

Deletes all of the completed logs.

Throws:

IOException

completeCurrentLog

void completeCurrentLog()
                 throws IOException

Marks the current log as completed. If successful, the current log will no longer exist. The current log must be closed before this call.

Throws:

IOException