Package io.microraft.persistence

Class NopRaftStore

  • All Implemented Interfaces:
    RaftStore
    public class NopRaftStore
extends Object
implements RaftStore
    Used when a Raft node works transiently (its state is not persisted).

    • Constructor Summary

      Constructors 
      Constructor Description
      NopRaftStore()  

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void deleteSnapshotChunks​(long logIndex, int snapshotChunkCount)
      Deletes persisted snapshot chunks at the given log index.
      void flush()
      Forces all buffered (in any layer) Raft log changes to be written to the storage and returns after those changes are written.
      void persistAndFlushInitialGroupMembers​(io.microraft.model.log.RaftGroupMembersView initialGroupMembers)
      Persists and flushes the given initial Raft group members.
      void persistAndFlushLocalEndpoint​(io.microraft.model.persistence.RaftEndpointPersistentState localEndpointPersistentState)
      Persists and flushes the given local Raft endpoint and its voting flag.
      void persistAndFlushTerm​(io.microraft.model.persistence.RaftTermPersistentState termPersistentState)
      Persists the term and the Raft endpoint that the local Raft node voted for in the given term.
      void persistLogEntries​(List<io.microraft.model.log.LogEntry> logEntries)
      Persists the given log entries.
      void persistSnapshotChunk​(io.microraft.model.log.SnapshotChunk snapshotChunk)
      Persists the given snapshot chunk.
      void truncateLogEntriesFrom​(long logIndexInclusive)
      Rolls back the log by truncating all entries starting with the given index.
      void truncateLogEntriesUntil​(long logIndexInclusive)
      MicroRaft calls this method after it successfully persists and flushes a snapshot.

    • Constructor Detail

      • NopRaftStore

        public NopRaftStore()

    • Method Detail

      • persistAndFlushLocalEndpoint

        public void persistAndFlushLocalEndpoint​(@Nonnull
                                         io.microraft.model.persistence.RaftEndpointPersistentState localEndpointPersistentState)
        Description copied from interface: RaftStore
        Persists and flushes the given local Raft endpoint and its voting flag.

        When this method returns, all the provided data has become durable.

        Specified by:
        persistAndFlushLocalEndpoint in interface RaftStore
        Parameters:
        localEndpointPersistentState - the local endpoint state to be persisted

      • persistAndFlushInitialGroupMembers

        public void persistAndFlushInitialGroupMembers​(@Nonnull
                                               io.microraft.model.log.RaftGroupMembersView initialGroupMembers)
        Description copied from interface: RaftStore
        Persists and flushes the given initial Raft group members.

        When this method returns, all the provided data has become durable.

        Specified by:
        persistAndFlushInitialGroupMembers in interface RaftStore
        Parameters:
        initialGroupMembers - the initial Raft group member list to persist

      • persistAndFlushTerm

        public void persistAndFlushTerm​(@Nonnull
                                io.microraft.model.persistence.RaftTermPersistentState termPersistentState)
        Description copied from interface: RaftStore
        Persists the term and the Raft endpoint that the local Raft node voted for in the given term.

        When this method returns, all the provided data has become durable.

        Specified by:
        persistAndFlushTerm in interface RaftStore
        Parameters:
        termPersistentState - the term state to be persisted

      • persistLogEntries

        public void persistLogEntries​(@Nonnull
                              List<io.microraft.model.log.LogEntry> logEntries)
                       throws IOException
        Description copied from interface: RaftStore
        Persists the given log entries.

        Log entries are appended to the Raft log with sequential log indices. The first log index is 1.

        A block of consecutive log entries has no gaps in the indices, but a gap can appear between a snapshot entry and its preceding regular log entry. This happens in an edge case where a follower has fallen so far behind that the missing entries are no longer available from the leader. In that case the leader will send its snapshot entry instead.

        In another rare failure scenario, MicroRaft can delete a range of the latest entries which are uncommitted and roll back to a previous log index which is known to be committed. Consider the following case where Raft persists 3 log entries and then deletes entries from index=2:

        • persistLogEntries(1, 2, 3)
        • truncateLogEntriesFrom(2)
        After this call sequence log indices will remain sequential and the next persistLogEntries() call will be for index=2.
        Specified by:
        persistLogEntries in interface RaftStore
        Parameters:
        logEntries - the list of log entries to be persisted
        Throws:
        IOException - if any failure occurs during persisting the given log entry
        See Also:
        RaftStore.flush(), RaftStore.persistSnapshotChunk(SnapshotChunk), RaftStore.truncateLogEntriesFrom(long), RaftConfig

      • persistSnapshotChunk

        public void persistSnapshotChunk​(@Nonnull
                                 io.microraft.model.log.SnapshotChunk snapshotChunk)
        Description copied from interface: RaftStore
        Persists the given snapshot chunk.

        A snapshot is persisted with at least 1 chunk. The number of chunks in a snapshot is provided via SnapshotChunk.getSnapshotChunkCount(). A snapshot is considered to be complete when all of its chunks are provided to this method in any order, and RaftStore.flush() will be called afterwards.

        MicroRaft takes snapshots at a predetermined interval, controlled by RaftConfig.getCommitCountToTakeSnapshot(). For instance, if it is 100, snapshots will occur at indices 100, 200, 300, and so on.

        The snapshot index can lag behind the index of the highest log entry which was already persisted and flushed, but there is an upper bound to this difference, controlled by RaftConfig.getMaxPendingLogEntryCount(). For instance, if it is 10, and a persistSnapshot() call is made with snapshotIndex=100, the index of the preceding persistLogEntries() call can be at most 110.

        On the other hand, the snapshot index can also be ahead of the highest log entry. This can happen when a Raft follower has fallen so far behind the leader and the leader no longer holds the missing entries. In that case, the follower receives a snapshot from the leader. There is no upper-bound on the gap between the highest log entry and the index of the received snapshot.

        Specified by:
        persistSnapshotChunk in interface RaftStore
        Parameters:
        snapshotChunk - the snapshot chunk object to persist
        See Also:
        RaftStore.flush(), RaftStore.persistLogEntries(List), RaftConfig

      • truncateLogEntriesFrom

        public void truncateLogEntriesFrom​(long logIndexInclusive)
        Description copied from interface: RaftStore
        Rolls back the log by truncating all entries starting with the given index. A truncated log entry is no longer valid and must not be restored (or at least must be ignored during the restore process).

        There is an upper-bound on the number of persisted log entries that can be truncated afterwards, which is specified by RaftConfig.getMaxPendingLogEntryCount() + 1. Say that it is 5 and the highest persisted log entry index is 20. Then, at most 5 highest entries can be truncated, hence truncation can start at index=16 or higher.

        Specified by:
        truncateLogEntriesFrom in interface RaftStore
        Parameters:
        logIndexInclusive - the log index value from which the log entries must be truncated
        See Also:
        RaftStore.flush(), RaftStore.persistLogEntries(List), RaftConfig

      • truncateLogEntriesUntil

        public void truncateLogEntriesUntil​(long logIndexInclusive)
        Description copied from interface: RaftStore
        MicroRaft calls this method after it successfully persists and flushes a snapshot. This method is used for deleting log entries and snapshot chunks that are before the snapshot index and are not needed to be restored. This is merely an optimization method and its side-effects can be sync'ed to the storage when RaftStore.flush() is called,
        Specified by:
        truncateLogEntriesUntil in interface RaftStore
        Parameters:
        logIndexInclusive - the log index value until which the log entries and snapshot chunks must be truncated

      • deleteSnapshotChunks

        public void deleteSnapshotChunks​(long logIndex,
                                 int snapshotChunkCount)
        Description copied from interface: RaftStore
        Deletes persisted snapshot chunks at the given log index. MicroRaft calls this method when it detects that it needs to start installing a newer snapshot while there is a snapshot persisted partially. Those snapshot chunks are no longer valid and must not be restored (or at least must be ignored during the restore process). This is merely an optimization method and its side-effects can be sync'ed to the storage when RaftStore.flush() is called.
        Specified by:
        deleteSnapshotChunks in interface RaftStore
        Parameters:
        logIndex - the log index value at which some snapshot chunks are persisted.
        snapshotChunkCount - the number of snapshot chunks that could have been persisted.