Struct DoubleWriteBuffer 

pub struct DoubleWriteBuffer { /* private fields */ }

Double-write buffer file.

Implementations

impl DoubleWriteBuffer

pub fn open(path: &Path) -> Result<Self>

Open or create the double-write buffer file.

pub fn write_record(&mut self, record: &WalRecord) -> Result<()>

Write a WAL record to the double-write buffer before WAL append.

The record is written at the current circular position and the file is fsynced immediately. Use write_record_deferred + flush for batch mode (multiple records per fsync).

pub fn write_record_deferred(&mut self, record: &WalRecord) -> Result<()>

Write a WAL record to the DWB without fsyncing.

The data is written to the OS page cache but not guaranteed durable until flush() is called. Use this in batch mode: write all records in a group commit batch, then call flush() once — reducing fsync calls from N-per-batch to 1-per-batch.

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

Flush the DWB header and fsync the file.

Must be called after one or more write_record_deferred calls to make the records durable. The single fsync covers all deferred writes since the last flush — amortizing the cost across the group commit batch.

pub fn path(&self) -> &Path

Path to the double-write buffer file.

pub fn recover_record(&mut self, target_lsn: u64) -> Result<Option<WalRecord>>

Try to recover a WAL record by LSN from the double-write buffer.

Scans all DWB_CAPACITY slots for a record matching the given LSN with valid CRC. We scan every slot rather than relying on count or write_pos because the header itself may be stale or corrupted after a crash. Each slot is self-describing: the record’s own CRC validates whether the slot contains usable data.

Trait Implementations

impl Debug for DoubleWriteBuffer

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

Formats the value using the given formatter.