alluxio.master.journal.ufs

Class UfsJournalReader

java.lang.Object

alluxio.master.journal.ufs.UfsJournalReader

All Implemented Interfaces:

JournalReader, Closeable, AutoCloseable

@NotThreadSafe
public final class UfsJournalReader
extends Object
implements JournalReader

Implementation of JournalReader that reads journal entries from a UFS. It can optionally read after a given sequence number. By default, it starts from 0 sequence number. If this reader runs in a primary master, it reads the incomplete log. If this reader runs in a secondary master, it does not read the incomplete log.

Nested Class Summary

Nested classes/interfaces inherited from interface alluxio.master.journal.JournalReader

JournalReader.State

Constructor Summary

Constructors

Constructor and Description
UfsJournalReader(UfsJournal journal, long startSequenceId, boolean readIncompleteLog) Creates a new instance of UfsJournalReader.

Method Summary

Modifier and Type	Method and Description
JournalReader.State	advance() Advances the reader to the next element.
void	close()
CheckpointInputStream	getCheckpoint() Returns the input stream for reading a checkpoint.
Journal.JournalEntry	getEntry() Returns the next entry in the journal.
static OptionalLong	getLastSN(UfsJournal journal) Iterates over the journal files searching for the greatest SN of all the files.
long	getNextSequenceNumber() Gets the the sequence number of the next journal log entry to read.

Methods inherited from class java.lang.Object

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

Constructor Detail

UfsJournalReader

public UfsJournalReader(UfsJournal journal,
                        long startSequenceId,
                        boolean readIncompleteLog)

Creates a new instance of UfsJournalReader.

Parameters:

journal - the handle to the journal

startSequenceId - the sequence ID to start reading from

readIncompleteLog - whether to read incomplete logs

Method Detail

close

public void close()
           throws IOException

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Throws:

IOException

getNextSequenceNumber

public long getNextSequenceNumber()

Description copied from interface: JournalReader

Gets the the sequence number of the next journal log entry to read. This method is valid no matter whether this JournalReader is closed or not.

Specified by:

getNextSequenceNumber in interface JournalReader

Returns:

the next sequence number

getCheckpoint

public CheckpointInputStream getCheckpoint()

Description copied from interface: JournalReader

Returns the input stream for reading a checkpoint. This will be null unless the last call to JournalReader.advance() returned JournalReader.State.CHECKPOINT. Multiple calls to getCheckpoint without calling advance will return the same stream.

Specified by:

getCheckpoint in interface JournalReader

Returns:

the input stream for reading the checkpoint, or null if the next element isn't a checkpoint

getEntry

public Journal.JournalEntry getEntry()

Description copied from interface: JournalReader

Returns the next entry in the journal. This will be null unless the last call to JournalReader.advance() returned JournalReader.State.LOG. Multiple calls to getEntry without calling advance will return the same entry.

Specified by:

getEntry in interface JournalReader

Returns:

the journal entry, or null if the next element isn't a journal entry

advance

public JournalReader.State advance()
                            throws IOException

Description copied from interface: JournalReader

Advances the reader to the next element.

Specified by:

advance in interface JournalReader

Returns:

the next element, see JournalReader.State

Throws:

IOException

getLastSN

public static OptionalLong getLastSN(UfsJournal journal)

Iterates over the journal files searching for the greatest SN of all the files. This method doesn't actually read the files, so the performance is just dependent on how fast the files can be iterated over.

Parameters:

journal - the UFS journal to get the final sequence number

Returns:

the final sequence number in the journal, or empty if an error occurred