class Raft::Log::File

Raft::Log::File
Raft::Log
Reference
Object

Overview

On-disk log storage backend with crash recovery.

Stores log entries in an append-only binary file (log.bin), metadata in metadata.bin, and snapshots in snapshot.bin. All multi-byte integers use big-endian encoding. Metadata and snapshot files are written atomically via tmp+rename.

Entry record format: [Index:8B][Term:8B][Type:1B][DataLen:4B][Data:NB]

By default every write is followed by an fsync(2) syscall so that entries are durable against power loss or kernel panics. Pass fsync: false to skip the syscall and rely on OS page-cache writeback instead — acceptable when an external restore path exists (replicated block storage, periodic backups, or a peer that always holds the full log).

log = Raft::Log::File.new("/var/lib/raft/node-1")               # fsync on (default)
log = Raft::Log::File.new("/var/lib/raft/node-1", fsync: false) # page-cache only

Defined in:

raft/log/file.cr

Constructors

.new(data_dir : String, fsync : Bool = true)
Creates a new file-backed log in the given data_dir.

Instance Method Summary

#append(entries : Array(Entry)) : Nil
Appends entries to the log with conflict detection.
#close : Nil
Releases any resources held by the log (e.g., file handles).
#get(index : UInt64) : Entry | Nil
Returns the entry at the given 1-based index, or nil if not present.
#last_index : UInt64
Returns the index of the last entry, or 0 if the log is empty.
#last_term : UInt64
Returns the term of the last entry, or 0 if the log is empty.
#load_metadata : Metadata
Loads the persisted metadata, or returns defaults (term 0, no vote).
#load_snapshot : Tuple(UInt64, UInt64, Bytes) | Nil
Loads the most recent snapshot, or returns nil if none exists.
#save_metadata(meta : Metadata) : Nil
Persists the node's current term and voted-for state.
#save_snapshot(last_index : UInt64, last_term : UInt64, data : Bytes) : Nil
Saves a snapshot and compacts the log up to last_index.
#slice(from : UInt64, to : UInt64) : Array(Entry)
Returns entries in the inclusive range [from, to].
#term_at(index : UInt64) : UInt64 | Nil
Returns the term of the entry at index, or nil if not present.
#truncate_from(index : UInt64) : Nil
Removes all entries at index and beyond (inclusive).

Instance methods inherited from class `Raft::Log`

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Constructor Detail

def self.new(data_dir : String, fsync : Bool = true) #

Creates a new file-backed log in the given data_dir.

The directory is created if it doesn't exist. On startup, the log file is scanned to rebuild the in-memory offset index.

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