Struct FileStore 

pub struct FileStore {
    dir: PathBuf,
    txn_dir: PathBuf,
    journal: File,
    capacity: u64,
}

dir/journal (preallocated), dir/checkpoint, dir/sentinel (4 KB, reserved at install), dir/lock, and fences at dir/../txn/<txn>/lease.

Filesystem-specific setup (chattr +C on btrfs, a dataset reservation on ZFS) is the installer’s job (§12c). This type only fallocates.

Fields

dir: PathBuf

txn_dir: PathBuf

journal: File

capacity: u64

Implementations

impl FileStore

pub fn open(dir: &Path, txn_dir: &Path, capacity: u64) -> Result<FileStore>

fn sync_txn_dir(&self) -> Result<()>

§12 step 4: a transaction’s fence directory is durable before the journal records the transaction as Prepared. replace_atomically fsyncs the directory the lease is in; the entry naming that directory lives in txn_dir, so txn_dir is fsynced once it is created. Without it a power loss could keep Prepared and lose the fence (fails safe, as an unfenced transaction, but not §12’s intent).

fn replace_atomically(&self, target: &Path, bytes: &[u8]) -> Result<()>

Trait Implementations

impl Debug for FileStore

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Store for FileStore

type Guard = File

The open lock file; closing it releases the flock.

fn lock(&self) -> Result<File>

fn capacity(&self) -> u64

fn read_at(&self, off: u64, len: usize) -> Result<Vec<u8>>

Up to len bytes at off; shorter at the end of the preallocation.

fn write_at(&self, off: u64, bytes: &[u8]) -> Result<()>

fn sync(&self) -> Result<()>

fn read_checkpoint(&self) -> Result<Option<Vec<u8>>>

fn write_checkpoint(&self, bytes: &[u8]) -> Result<()>

Atomic: either the old checkpoint or the complete new one survives.

fn read_sentinel(&self) -> Result<Option<Vec<u8>>>

fn write_sentinel(&self, bytes: &[u8]) -> Result<()>

fn fence(&self, txn: TxnId) -> Result<Option<u64>>

The epoch backends fence on. Written before the journal’s Takeover record.

fn set_fence(&self, txn: TxnId, epoch: u64) -> Result<()>

fn create_fence(&self, txn: TxnId, epoch: u64) -> Result<()>

A new transaction’s fence, created exclusively (§9 step 4, C5): fails with AlreadyExists if anything is already there for this id.

fn forget_fences<F: Fn(TxnId) -> bool>(&self, keep: F) -> Result<Vec<TxnId>>

Removes the fence of every transaction keep rejects; returns them. A transaction without a fence is never admitted, so this only narrows.