Struct Wal

pub struct Wal {
    dir: PathBuf,
    config: WalConfig,
    meta: WalMeta,
    current_writer: Option<BufWriter<File>>,
    current_segment_size: u64,
}

Write-Ahead Log.

Fields

dir: PathBuf

config: WalConfig

meta: WalMeta

current_writer: Option<BufWriter<File>>

current_segment_size: u64

Implementations

impl Wal

pub fn open(dir: &Path, config: WalConfig) -> Result<Self, StorageError>

Open or create a WAL in the given directory.

fn load_or_create_meta(dir: &Path) -> Result<WalMeta, StorageError>

fn segment_path(&self, segment_id: u64) -> PathBuf

fn open_current_segment(&mut self) -> Result<(), StorageError>

fn write_segment_header( writer: &mut BufWriter<File>, segment_id: u64, ) -> Result<(), StorageError>

fn rotate_segment(&mut self) -> Result<(), StorageError>

pub fn append( &mut self, entry_type: EntryType, flags: u8, payload: &[u8], ) -> Result<u64, StorageError>

Append an entry to the WAL. Returns the assigned sequence number.

pub fn commit(&mut self, sequence: u64) -> Result<(), StorageError>

Mark all entries up to sequence as committed.

Ensures durability by syncing segment data to disk before updating metadata, then syncing the directory to make the rename durable. See RFC-002-01 (Pillai et al., OSDI 2014).

pub fn committed_sequence(&self) -> u64

Get the last committed sequence number.

pub fn last_sequence(&self) -> u64

Get the last appended sequence number.

pub fn flush(&mut self) -> Result<(), StorageError>

Flush buffered writes to disk.

fn persist_meta(&self) -> Result<(), StorageError>

pub fn recover(&mut self) -> Result<Vec<WalEntry>, StorageError>

Recover uncommitted entries after a crash.

Scans all segments for entries with sequence > committed_sequence. Validates CRC32 for each entry. Stops at first corrupted entry. Returns valid uncommitted entries for replay.

fn list_segments(&self) -> Result<Vec<u64>, StorageError>

fn read_segment( &self, segment_id: u64, committed_seq: u64, ) -> Result<Vec<WalEntry>, StorageError>

pub fn truncate_uncommitted(&mut self) -> Result<(), StorageError>

Truncate the WAL at the current committed position.

Removes all segments before the committed segment and truncates the committed segment at the committed offset. Used after recovery.