README
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fsm
FSM stands for Finite State Machine
The fsm package contains the RavelFSM and Snapshot structs that implements
the FSM interface and
the FSMSnapshot interface respectively which are required
for constructing a new raft node in
the hashicorp/raft library
These interfaces are responsible for actually "applying" the log entries to our BadgerDB instance in a persistent manner.
RavelFSM
This struct implements the FSM interface. This interface makes use of the replicated log to "apply" logs, take snapshots and "restore" from snapshots.
-
The
Applyfunction is invoked once a log entry is committed and is responsible for storing the data to the BadgerDB instance. It checks the type of operation it is required to perform and then calls the corresponding function from thedbpackage. -
The
Snapshotfunction is used for log compaction. Its returns aSnapshotobject (a struct which implements the FSMSnapshot interface) which is used to save a snapshot of the FSM at that point in time i.e. its takes the state of the DB and creates a copy of the state so that previous logs can be deleted. -
The
Restorefunction is used to restore an FSM from a snapshot i.e. restore the state of the DB to when the snapshot was taken thereby discarding all the previous states. This can be done very easily using BadgerDB's inbuilt functions, first we drop all the current keys using the DropAll function and then call the Load function to restore the snapshot from backup.
Snapshot
This struct implements the FSMSnapshot interface. Snapshot
is returned by an FSM in response to a Snapshot call. This interface is responsible for dumping the current state of the
DB i.e. snapshot of the FSM to the WriteCloser
sink which stored by the raft lib.
-
Persistis the main function which dumps the snapshot to the sink. We do this by simply taking a backup of our db and writing it into the sink. -
Releaseis called when we are finished with the snapshot and all the data has been safely dumped.
Documentation
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Index ¶
Constants ¶
This section is empty.
Variables ¶
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Functions ¶
This section is empty.
Types ¶
type LogData ¶
type LogData struct {
Operation string `json:"Operation"`
Key []byte `json:"Key"`
Value []byte `json:"Value"`
}
LogData represents the structure of individual commands on the Logs
type RavelFSM ¶
type RavelFSM struct {
Db *db.RavelDatabase
}
RavelFSM implements the raft.FSM interface. It represents the Finite State Machine in a RavelNode. The individual logs are "applied" on the FSM on receiving the commit RPC from the leader.
func (*RavelFSM) Close ¶
func (f *RavelFSM) Close()
Close will close the connection to the internal db.RavelDatabase instance
func (*RavelFSM) GetAndDelete ¶
Get returns the value for the provided key
type Snapshot ¶
type Snapshot struct {
Db *db.RavelDatabase
}
Snapshot implements the raft.Snapshot interface
Source Files