All Known Implementing Classes:

NopRaftStore
```
public interface RaftStore
```
This interface is used for persisting only the internal state of the Raft consensus algorithm. Internal state of StateMachine implementations are not persisted with this interface.
A RaftStore implementation can implement RaftNodeLifecycleAware to perform initialization and clean up work during RaftNode startup and termination. RaftNode calls RaftNodeLifecycleAware.onRaftNodeStart() before calling any other method on RaftStore, and finally calls RaftNodeLifecycleAware.onRaftNodeTerminate() on termination.

See Also:

RaftModel, RaftModelFactory, RaftNode

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`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(RaftGroupMembersView initialGroupMembers)`	Persists and flushes the given initial Raft group members.
`void`	`persistAndFlushLocalEndpoint(RaftEndpoint localEndpoint, boolean localEndpointVoting)`	Persists and flushes the given local Raft endpoint and its voting flag.
`void`	`persistAndFlushTerm(int term, RaftEndpoint votedFor)`	Persists the term and the Raft endpoint that the local Raft node voted for in the given term.
`void`	`persistLogEntry(LogEntry logEntry)`	Persists the given log entry.
`void`	`persistSnapshotChunk(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`	`truncateSnapshotChunksUntil(long logIndexInclusive)`	Rolls back the persisted snapshot chunks only when all of the expected snapshot chunks are not already persisted.

- Method Detail
  - persistAndFlushLocalEndpoint
```
void persistAndFlushLocalEndpoint(RaftEndpoint localEndpoint,
                                  boolean localEndpointVoting)
                           throws IOException
```
    Persists and flushes the given local Raft endpoint and its voting flag.
    When this method returns, all the provided data has become durable.
    
    Parameters:
    
    localEndpoint - the Raft endpoint of the local Raft node to persist
    
    localEndpointVoting - the flag that denotes whether if the local Raft node is a voting or non-voting member
    
    Throws:
    
    IOException - if any failure occurs during persisting the given values
  - persistAndFlushInitialGroupMembers
```
void persistAndFlushInitialGroupMembers(@Nonnull
                                        RaftGroupMembersView initialGroupMembers)
                                 throws IOException
```
    Persists and flushes the given initial Raft group members.
    When this method returns, all the provided data has become durable.
    
    Parameters:
    
    initialGroupMembers - the initial Raft group member list to persist
    
    Throws:
    
    IOException - if any failure occurs during persisting the given values
  - persistAndFlushTerm
```
void persistAndFlushTerm(int term,
                         @Nullable
                         RaftEndpoint votedFor)
                  throws IOException
```
    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.
    
    Parameters:
    
    term - the term value to persist
    
    votedFor - the voted Raft endpoint to persist
    
    Throws:
    
    IOException - if any failure occurs during persisting the given values
  - persistLogEntry
```
void persistLogEntry(@Nonnull
                     LogEntry logEntry)
              throws IOException
```
    Persists the given log entry.
    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, Raft must delete a range of the highest entries, rolling back the index of the next persisted entry. Consider the following case where Raft persists 3 log entries and then deletes entries from index=2:
    
    persistLogEntry(1)
    persistLogEntry(2)
    persistLogEntry(3)
    truncateLogEntriesFrom(2)
    After this call sequence log indices will remain sequential and the next persistLogEntry() call will be for index=2.
    Parameters:
    
    logEntry - the log entry object to persist
    
    Throws:
    
    IOException - if any failure occurs during persisting the given log entry
    
    See Also:
    
    flush(), persistSnapshotChunk(SnapshotChunk), truncateLogEntriesFrom(long), RaftConfig
  - persistSnapshotChunk
```
void persistSnapshotChunk(@Nonnull
                          SnapshotChunk snapshotChunk)
                   throws IOException
```
    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 flush() could be called afterwards.
    After a snapshot is persisted at index=i and flush() is called, the log entry at index=i, all the preceding log entries, and all the preceding snapshots are no longer needed and can be evicted from storage. Failing to evict stale entries and snapshots do not cause a consistency problem, but can increase the time to recover after a crash or restart. Therefore eviction can be done in a background task.
    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 that 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 persistLogEntry() 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.
    
    Parameters:
    
    snapshotChunk - the snapshot chunk object to persist
    
    Throws:
    
    IOException - if any failure occurs during persisting the given snapshot chunk
    
    See Also:
    
    flush(), persistLogEntry(LogEntry), RaftConfig
  - truncateLogEntriesFrom
```
void truncateLogEntriesFrom(long logIndexInclusive)
                     throws IOException
```
    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.
    
    Parameters:
    
    logIndexInclusive - the log index value from which the log entries must be truncated
    
    Throws:
    
    IOException - if any failure occurs during truncating the log entries
    
    See Also:
    
    flush(), persistLogEntry(LogEntry), RaftConfig
  - truncateSnapshotChunksUntil
```
void truncateSnapshotChunksUntil(long logIndexInclusive)
                          throws IOException
```
    Rolls back the persisted snapshot chunks only when all of the expected snapshot chunks are not already persisted. A truncated snapshot chunk is no longer valid and must not be restored (or at least must be ignored during the restore process).
    
    Parameters:
    
    logIndexInclusive - the log index value until which the log entries must be truncated
    
    Throws:
    
    IOException - if any failure occurs during truncating the log entries
    
    See Also:
    
    persistSnapshotChunk(SnapshotChunk)
  - flush
```
void flush()
    throws IOException
```
    Forces all buffered (in any layer) Raft log changes to be written to the storage and returns after those changes are written.
    When this method returns, all the changes done via the other methods have become durable.
    
    Throws:
    
    IOException - if any failure occurs during the flush operation
    
    See Also:
    
    persistLogEntry(LogEntry), persistSnapshotChunk(SnapshotChunk), truncateSnapshotChunksUntil(long), truncateLogEntriesFrom(long)

Interface RaftStore

Method Summary

Method Detail

persistAndFlushLocalEndpoint

persistAndFlushInitialGroupMembers

persistAndFlushTerm

persistLogEntry

persistSnapshotChunk

truncateLogEntriesFrom

truncateSnapshotChunksUntil

flush