alluxio.master.journal

Class FileSystemMergeJournalContext

java.lang.Object

alluxio.master.journal.FileSystemMergeJournalContext

All Implemented Interfaces:

JournalContext, Closeable, AutoCloseable, java.util.function.Supplier<JournalContext>

Direct Known Subclasses:

MetadataSyncMergeJournalContext

@ThreadSafe
public class FileSystemMergeJournalContext
extends Object
implements JournalContext

Context for merging journal entries together for a wrapped journal context. This is used so that we can combine several journal entries into one using a merge function. This helps us resolve the inconsistency between primary and standby and decrease the chance for a standby to see intermediate state of a file system operation. This journal context is made thread-safe because metadata sync creates worker threads to fetch metadata and reuses the same journal context.

Field Summary

Fields

Modifier and Type	Field and Description
protected JournalEntryMerger	mJournalEntryMerger

Constructor Summary

Constructors

Constructor and Description
FileSystemMergeJournalContext(JournalContext journalContext, JournalEntryMerger journalEntryMerger) Constructs a FileSystemMergeJournalContext.

Method Summary

Modifier and Type	Method and Description
void	append(Journal.JournalEntry entry) Adds the new journal entry into the journal entry merger.
protected boolean	appendMergedJournals()
void	close()
void	flush() Merges all journals and then flushes them.
JournalContext	getUnderlyingJournalContext()

Methods inherited from class java.lang.Object

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

Methods inherited from interface alluxio.master.journal.JournalContext

get

Field Detail

mJournalEntryMerger

protected final JournalEntryMerger mJournalEntryMerger

Constructor Detail

FileSystemMergeJournalContext

public FileSystemMergeJournalContext(JournalContext journalContext,
                                     JournalEntryMerger journalEntryMerger)

Constructs a FileSystemMergeJournalContext.

Parameters:

journalContext - the journal context to wrap

journalEntryMerger - the merger which merges multiple journal entries into one

Method Detail

append

public void append(Journal.JournalEntry entry)

Adds the new journal entry into the journal entry merger. If the size of the outstanding journal entries are bigger than the threshold, we will flush them immediately into the async journal writer. This is used to prevent a recursive file system operation adding too many journal entries without being flushed and taking huge memory. Though it might create inconsistency between primary and standby if the primary crashes between two flushes. Tune PropertyKey.MASTER_MERGE_JOURNAL_CONTEXT_MAX_ENTRIES to trade off

Specified by:

append in interface JournalContext

Parameters:

entry - the Journal.JournalEntry to append to the journal

close

public void close()
           throws UnavailableException

Specified by:

close in interface JournalContext

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Throws:

UnavailableException

flush

public void flush()
           throws UnavailableException

Merges all journals and then flushes them. The journal writer will commit these journals synchronously.

Specified by:

flush in interface JournalContext

Throws:

UnavailableException

appendMergedJournals

protected boolean appendMergedJournals()

getUnderlyingJournalContext

public JournalContext getUnderlyingJournalContext()

Returns:

the underlying journal context