com.hazelcast.cp.internal.raft.impl.log

Class RaftLog

java.lang.Object

com.hazelcast.cp.internal.raft.impl.log.RaftLog

public class RaftLog
extends Object

RaftLog keeps and maintains Raft log entries and snapshot. Entries appended in leader's RaftLog are replicated to all followers in the same order and all nodes in a Raft group eventually keep the exact same copy of the RaftLog.

Raft maintains the following properties, which together constitute the LogMatching Property:

• If two entries in different logs have the same index and term, then they store the same command.
• If two entries in different logs have the same index and term, then the logs are identical in all preceding entries.

See Also:

LogEntry, SnapshotEntry

Constructor Summary

Constructors

Constructor and Description
RaftLog(int capacity)

Method Summary

Modifier and Type	Method and Description
void	appendEntries(LogEntry... newEntries) Appends new entries to the Raft log.
int	availableCapacity() Returns the number of empty indices in the Raft log
boolean	checkAvailableCapacity(int requestedCapacity) Returns true if the Raft log contains empty indices for the requested amount
boolean	containsLogEntry(long entryIndex) Returns true if the log contains an entry at entryIndex, false otherwise.
LogEntry[]	getEntriesBetween(long fromEntryIndex, long toEntryIndex) Returns log entries between fromEntryIndex and toEntryIndex, both inclusive.
LogEntry	getLogEntry(long entryIndex) Returns the log entry stored at entryIndex.
LogEntry	lastLogOrSnapshotEntry() Returns the last entry in the Raft log, either from the last log entry or from the last snapshot if no logs are available.
long	lastLogOrSnapshotIndex() Returns the last entry index in the Raft log, either from the last log entry or from the last snapshot if no logs are available.
int	lastLogOrSnapshotTerm() Returns the last term in the Raft log, either from the last log entry or from the last snapshot if no logs are available.
int	setSnapshot(SnapshotEntry snapshot) Installs the snapshot entry and truncates log entries those are included in snapshot (entries whose indexes are smaller than the snapshot's index).
int	setSnapshot(SnapshotEntry snapshot, long truncateUpToIndex)
SnapshotEntry	snapshot() Returns snapshot entry.
long	snapshotIndex() Returns snapshot entry index.
List<LogEntry>	truncateEntriesFrom(long entryIndex) Truncates log entries with indexes >= entryIndex.

Methods inherited from class java.lang.Object

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

Constructor Detail

RaftLog

public RaftLog(int capacity)

Method Detail

lastLogOrSnapshotIndex

public long lastLogOrSnapshotIndex()

Returns the last entry index in the Raft log, either from the last log entry or from the last snapshot if no logs are available.

lastLogOrSnapshotTerm

public int lastLogOrSnapshotTerm()

Returns the last term in the Raft log, either from the last log entry or from the last snapshot if no logs are available.

lastLogOrSnapshotEntry

public LogEntry lastLogOrSnapshotEntry()

Returns the last entry in the Raft log, either from the last log entry or from the last snapshot if no logs are available.

containsLogEntry

public boolean containsLogEntry(long entryIndex)

Returns true if the log contains an entry at entryIndex, false otherwise.

Important: Log entry indices start from 1, not 0.

getLogEntry

public LogEntry getLogEntry(long entryIndex)

Returns the log entry stored at entryIndex. Entry is retrieved only from the current log, not from the snapshot entry.

If no entry available at this index, then null is returned.

Important: Log entry indices start from 1, not 0.

truncateEntriesFrom

public List<LogEntry> truncateEntriesFrom(long entryIndex)

Truncates log entries with indexes >= entryIndex.

Returns:

truncated log entries

Throws:

IllegalArgumentException - If no entries are available to truncate, if entryIndex is greater than last log index or smaller than snapshot index.

availableCapacity

public int availableCapacity()

Returns the number of empty indices in the Raft log

checkAvailableCapacity

public boolean checkAvailableCapacity(int requestedCapacity)

Returns true if the Raft log contains empty indices for the requested amount

appendEntries

public void appendEntries(LogEntry... newEntries)

Appends new entries to the Raft log.

Throws:

IllegalArgumentException - If an entry is appended with a lower term than the last term in the log or if an entry is appended with an index not equal to index == lastIndex + 1.

getEntriesBetween

public LogEntry[] getEntriesBetween(long fromEntryIndex,
                                    long toEntryIndex)

Returns log entries between fromEntryIndex and toEntryIndex, both inclusive.

Throws:

IllegalArgumentException - If fromEntryIndex is greater than toEntryIndex, or if fromEntryIndex is equal to / smaller than snapshotIndex, or if fromEntryIndex is greater than last log index, or if toEntryIndex is greater than last log index.

setSnapshot

public int setSnapshot(SnapshotEntry snapshot)

Installs the snapshot entry and truncates log entries those are included in snapshot (entries whose indexes are smaller than the snapshot's index).

Returns:

truncated log entries after snapshot is installed

Throws:

IllegalArgumentException - if the snapshot's index is smaller than or equal to current snapshot index

setSnapshot

public int setSnapshot(SnapshotEntry snapshot,
                       long truncateUpToIndex)

snapshotIndex

public long snapshotIndex()

Returns snapshot entry index.

snapshot

public SnapshotEntry snapshot()

Returns snapshot entry.