Struct CoreWalWriter 

pub struct CoreWalWriter { /* private fields */ }

Per-core WAL writer.

Each core owns its own writer, eliminating cross-core synchronization on the write path. Record format is compatible with [length: 4][crc32: 4][data: length]

Implementations

impl CoreWalWriter

pub fn new(core_id: usize, path: &Path) -> Result<Self, PerCoreWalError>

Creates a new per-core WAL writer.

Arguments

• core_id - The core ID for this writer
• path - Path to the segment file

Errors

Returns an error if the file cannot be created or opened.

pub fn open_at( core_id: usize, path: &Path, position: u64, ) -> Result<Self, PerCoreWalError>

Opens an existing segment file at a specific position.

Used during recovery to resume writing.

Errors

Returns an error if the file cannot be opened or truncated.

pub fn core_id(&self) -> usize

Returns the core ID for this writer.

pub fn position(&self) -> u64

Returns the current write position in bytes (includes un-synced data).

pub fn synced_position(&self) -> u64

Returns the last synced position (durable after fdatasync).

Only data up to this position is guaranteed to survive a crash. Use this for checkpoint manifests instead of position().

pub fn epoch(&self) -> u64

Returns the current epoch.

pub fn sequence(&self) -> u64

Returns the current sequence number.

pub fn path(&self) -> &Path

Returns the path to the segment file.

pub fn entries_since_sync(&self) -> u64

Returns the number of entries since last sync.

pub fn set_epoch(&mut self, epoch: u64)

Sets the current epoch (called by manager during checkpoint).

pub fn append_put( &mut self, key: &[u8], value: &[u8], ) -> Result<u64, PerCoreWalError>

Appends a Put operation to the WAL.

Errors

Returns an error if serialization or I/O fails.

pub fn append_delete(&mut self, key: &[u8]) -> Result<u64, PerCoreWalError>

Appends a Delete operation to the WAL.

Errors

Returns an error if serialization or I/O fails.

pub fn append_put_via_storage_io( &mut self, key: &[u8], value: &[u8], sio: &mut dyn StorageIo, fd: IoFd, ) -> Result<u64, PerCoreWalError>

Appends a Put operation via [StorageIo].

Errors

Returns an error if serialization or I/O submission fails.

pub fn append_delete_via_storage_io( &mut self, key: &[u8], sio: &mut dyn StorageIo, fd: IoFd, ) -> Result<u64, PerCoreWalError>

Appends a Delete operation via [StorageIo].

Errors

Returns an error if serialization or I/O submission fails.

pub fn append( &mut self, entry: &PerCoreWalEntry, ) -> Result<u64, PerCoreWalError>

Appends a raw entry to the WAL.

Record format: [length: 4 bytes][crc32: 4 bytes][data: length bytes]

Errors

Returns an error if serialization or I/O fails.

pub fn append_via_storage_io( &mut self, entry: &PerCoreWalEntry, sio: &mut dyn StorageIo, fd: IoFd, ) -> Result<u64, PerCoreWalError>

Appends a raw entry to the WAL via a [StorageIo] backend.

Identical to append but uses non-blocking I/O. The caller must poll sio.poll_completions() to drain completions.

Errors

Returns an error if serialization fails or the I/O submission fails.

pub fn sync_via_storage_io( &mut self, sio: &mut dyn StorageIo, fd: IoFd, ) -> Result<u64, PerCoreWalError>

Syncs the WAL segment via a [StorageIo] backend.

Submits an fdatasync through the I/O backend. Non-blocking — the caller must poll for the completion token.

Errors

Returns an error if the submission fails.

pub fn check_completions( &mut self, completions: &[IoCompletion], ) -> Result<bool, PerCoreWalError>

Check I/O completions and update sync state.

Scans completions for the pending sync token. If found and successful, calls mark_synced. If found and failed (negative result = errno), returns an error.

Returns Ok(true) if the sync completed successfully, Ok(false) if no matching completion was found, or Err if the sync failed.

Call this after every StorageIo::poll_completions round.

Errors

Returns PerCoreWalError::Io if the kernel reported a sync failure.

pub fn is_sync_pending(&self) -> bool

Returns true if a sync is pending (submitted but not yet completed).

pub fn mark_synced(&mut self)

Mark the current write position as synced (durable).

Used by the direct (non-StorageIo) sync path after a blocking fdatasync where all data up to position is guaranteed durable. The StorageIo path uses Self::check_completions instead, which advances only to the boundary recorded at submission time.

pub fn append_checkpoint( &mut self, checkpoint_id: u64, ) -> Result<u64, PerCoreWalError>

Appends a Checkpoint marker to the WAL.

Errors

Returns an error if serialization or I/O fails.

pub fn append_epoch_barrier(&mut self) -> Result<u64, PerCoreWalError>

Appends an EpochBarrier to the WAL.

Errors

Returns an error if serialization or I/O fails.

pub fn append_commit( &mut self, offsets: HashMap<String, u64>, watermark: Option<i64>, ) -> Result<u64, PerCoreWalError>

Appends a Commit entry to the WAL.

Errors

Returns an error if serialization or I/O fails.

pub fn sync(&mut self) -> Result<(), PerCoreWalError>

Syncs the WAL segment to disk using fdatasync.

Uses sync_data() instead of sync_all() for better performance.

Errors

Returns an error if the sync fails.

pub fn truncate(&mut self, position: u64) -> Result<(), PerCoreWalError>

Truncates the segment file at the specified position.

Used after checkpoint to remove entries that have been checkpointed.

Errors

Returns an error if truncation fails.

pub fn reset(&mut self) -> Result<(), PerCoreWalError>

Resets the segment (truncates to zero).

Used after successful checkpoint to clear the WAL.

Errors

Returns an error if truncation fails.

Trait Implementations

impl Debug for CoreWalWriter

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

Formats the value using the given formatter.