Struct Lsn 

pub struct Lsn(/* private fields */);

A log sequence number: a record’s byte position in the log, assigned at append time.

An LSN is the byte offset where the record’s frame begins. The first record appended to a fresh log is Lsn(0); the next starts at the first record’s end, and so on. LSNs are therefore monotonic and unique but not consecutive — each one is larger than the last by exactly the previous record’s framed size. Defining the LSN as the offset is what lets the multi-writer append path stay lock-free: a single atomic reservation hands out the offset, and offset order is append order by construction, so two records can never share an LSN or land out of order.

A record’s LSN is stable for the life of the log and is the value returned by Record::lsn. Comparing two LSNs establishes which record came first.

The number is a u64. Even an exabyte log uses only 60 bits of it, so wraparound is not a concern this type guards against.

Examples

use wal_db::Lsn;

// The first record always starts at offset 0.
let first = Lsn::new(0);
// A later record sits at a higher offset; the exact value depends on the
// sizes of the records before it.
let later = Lsn::new(64);

assert!(first < later);
assert_eq!(later.get(), 64);
assert_eq!(u64::from(later), 64);

Implementations

impl Lsn

pub const fn new(value: u64) -> Self

Construct an LSN from its raw u64 value.

This is rarely needed directly — Wal::append returns the LSN it assigned — but it is useful for comparisons and tests.

use wal_db::Lsn;
assert_eq!(Lsn::new(42).get(), 42);

pub const fn get(self) -> u64

Return the raw u64 value.

use wal_db::Lsn;
let lsn = Lsn::new(7);
assert_eq!(lsn.get(), 7);

Trait Implementations

impl Clone for Lsn

fn clone(&self) -> Lsn

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Lsn

impl Debug for Lsn

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

Formats the value using the given formatter.

impl Display for Lsn

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

Formats the value using the given formatter.

impl Eq for Lsn

impl From<Lsn> for u64

fn from(lsn: Lsn) -> Self

Converts to this type from the input type.

impl Hash for Lsn

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for Lsn

fn cmp(&self, other: &Lsn) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl PartialEq for Lsn

fn eq(&self, other: &Lsn) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd for Lsn

fn partial_cmp(&self, other: &Lsn) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl StructuralPartialEq for Lsn