org.neo4j.causalclustering.core.consensus.log

Interface RaftLog

All Superinterfaces:

ReadableRaftLog

All Known Implementing Classes:

DelegatingRaftLog, InMemoryRaftLog, MonitoredRaftLog, SegmentedRaftLog

public interface RaftLog
extends ReadableRaftLog

Persists entries that are coordinated through RAFT, i.e. this is the log of user data.

All write operations in this interface must be durably persisted before returning from the respective functions.

Field Summary

Fields

Modifier and Type	Field and Description
static String	PHYSICAL_LOG_DIRECTORY_NAME

Method Summary

Modifier and Type	Method and Description
long	append(RaftLogEntry... entry) Appends entry to the end of the log.
long	prune(long safeIndex) Attempt to prune (delete) a prefix of the log, no further than the safeIndex.
long	skip(long index, long term) Skip up to the supplied index if it is not already present.
void	truncate(long fromIndex) Truncates the log starting from the supplied index.

Methods inherited from interface org.neo4j.causalclustering.core.consensus.log.ReadableRaftLog

appendIndex, getEntryCursor, prevIndex, readEntryTerm

Field Detail

PHYSICAL_LOG_DIRECTORY_NAME

static final String PHYSICAL_LOG_DIRECTORY_NAME

See Also:

Constant Field Values

Method Detail

append

long append(RaftLogEntry... entry)
     throws IOException

Appends entry to the end of the log. The first log index is 0.

The entries must be uniquely identifiable and already appended entries must not be re-appended (unless they have been removed through truncation).

Parameters:

entry - The log entry.

Returns:

the index at which the entry was appended.

Throws:

IOException

truncate

void truncate(long fromIndex)
       throws IOException

Truncates the log starting from the supplied index. Committed entries can never be truncated.

Parameters:

fromIndex - The start index (inclusive).

Throws:

IOException

prune

long prune(long safeIndex)
    throws IOException

Attempt to prune (delete) a prefix of the log, no further than the safeIndex.

Implementations can choose to prune a shorter prefix if this is convenient for their storage mechanism. The return value tells the caller how much was actually pruned.

Parameters:

safeIndex - Highest index that may be pruned.

Returns:

The new prevIndex for the log, which will be at most safeIndex.

Throws:

IOException

skip

long skip(long index,
          long term)
   throws IOException

Skip up to the supplied index if it is not already present.

If the entry was not present then it gets defined with the supplied term, but without content, and thus can be used only for log matching from a later index.

This is useful when a snapshot starting from a later index has been downloaded and thus earlier entries are irrelevant and possibly non-existent in the cluster.

Parameters:

index - the index we want to skip to

term - the term of the index

Returns:

The appendIndex after this call, which will be at least index.

Throws:

IOException