raft_update — State updates

State changes or actions to handle after calling raft_step().

Data types

struct raft_update

The raft_update struct holds information about new state changes or actions that a user should handle after a call to raft_step(), such as:

• New data to persist on disk (e.g. new entries or snapshot)

• New messages to send to other Raft servers

• New term, vote, commit index, etc

Users of the core raft struct are responsible for implementing I/O and application code that manages the above state updates.

struct raft_update
{
    unsigned flags;
    struct { ,.. } entries;
    struct { ,.. } snapshot;
    struct { ,.. } messages;
    struct
};

Public members

unsigned raft_update.flags

Bit flags that indicate which particular state change or action should be processed:

#define RAFT_UPDATE_CURRENT_TERM 1 << 0
#define RAFT_UPDATE_VOTED_FOR 1 << 1
#define RAFT_UPDATE_ENTRIES 1 << 2
#define RAFT_UPDATE_SNAPSHOT 1 << 3
#define RAFT_UPDATE_MESSAGES 1 << 4
#define RAFT_UPDATE_STATE 1 << 5
#define RAFT_UPDATE_COMMIT_INDEX 1 << 6
#define RAFT_UPDATE_TIMEOUT 1 << 7

Current Term

RAFT_UPDATE_CURRENT_TERM

If this bit flag is on, the current term of raft struct has changed and must be durably persisted to disk. This has to be done before processing any other change or action (i.e. no messages must be sent until the new term has been persisted).

User code can use raft_current_term() to get the new term that should be persisted.

Voted for

RAFT_UPDATE_VOTED_FOR

If this bit flag is on, the server that the raft struct has voted for has changed and must be durably persisted to disk. This has to be done before processing any other change or action (i.e. no messages must be sent until the new vote has been persisted).

User code can use raft_voted_for() to get the server ID that should be persisted as new vote.

Entries

RAFT_UPDATE_ENTRIES

If this bit flag is on, a new batch of log entries should be persisted to disk, as described by the raft_update.entries field.

struct [anonymous] raft_update.entries

Details about new entries to persist.

struct
{
    raft_index index;         /* Index of first entry in the batch */
    struct raft_entry *batch; /* Array of entries to persist */
    unsigned n;               /* Number of entries in the array */
} entries;

Snapshot

RAFT_UPDATE_SNAPOSHOT

If this bit flag is on, a new snapshot chunk should be persisted to disk, as described by the raft_update.snapshot field.

struct [anonymous] raft_update.snapshot

Details about new entries to persist.

struct
{
    struct raft_snapshot_metadata metadata; /* Snapshot metadata */
    size_t offset;                          /* Chunk offset */
    struct raft_buffer chunk;               /* Data chunk */
    bool last;                              /* True if last chunk */
} snapshot;

Messages

RAFT_UPDATE_MESSAGES

If this bit flag is on, new messages should be sent, as described by the raft_update.messages field.

struct [anonymous] raft_update.messages

Details about new entries to persist.

struct
{
    struct raft_message *batch; /* Array of messages to send */
    unsigned n;                 /* Number of messages in the array */
} messages;

State

RAFT_UPDATE_STATE

If this bit flag is on, the raft_state of the raft struct has changed. The new state can be obtained with raft_state().

Commit index

RAFT_UPDATE_COMMIT_INDEX

If this bit flag is on, the commit index has changed. The new commit index can be obtained with raft_commit_index().

Timeout

RAFT_UPDATE_TIMEOUT

If this bit flag is on, the time at which the next RAFT_TIMEOUT event should be fired has changed. The new time can be obtained with raft_timeout().