Struct WalHeader 

pub struct WalHeader {
    pub magic: u64,
    pub version: u16,
    pub flags: u16,
    pub epoch: u64,
    pub writer_id: Uuid,
    pub last_commit_lsn: u64,
    pub last_entry_crc: u32,
    pub entry_count: u64,
    pub header_crc: u32,
}

WAL file header with epoch fencing

This header is stored in the first 64 bytes of every WAL file. It enables detection of concurrent writers and safe recovery.

Fields

magic: u64

Magic number (0x534F4348444257 = “SOCHDBW”)

version: u16

WAL format version

flags: u16

Reserved flags

epoch: u64

Epoch counter - incremented on each writer open

writer_id: Uuid

UUID of the current writer

last_commit_lsn: u64

LSN of the last committed transaction

last_entry_crc: u32

CRC of the last entry (for chain verification)

entry_count: u64

Number of entries written in current epoch

header_crc: u32

CRC32 of the header itself

Implementations

impl WalHeader

pub fn new() -> Self

Create a new header for a fresh WAL

pub fn new_epoch(previous: &WalHeader) -> Self

Create header for a new epoch (when taking over from previous writer)

pub fn read_from(file: &mut File) -> Result<Self>

Read header from file

pub fn write_to(&self, file: &mut File) -> Result<()>

Write header to file

pub fn update_last_entry_crc(&mut self, crc: u32)

Update last entry CRC (called after each write)

pub fn update_last_commit(&mut self, lsn: u64)

Update last commit LSN (called after each commit)

Trait Implementations

impl Clone for WalHeader

fn clone(&self) -> WalHeader

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for WalHeader

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

Formats the value using the given formatter.

impl Default for WalHeader

fn default() -> Self

Returns the “default value” for a type.