Struct Sequencer 

pub struct Sequencer { /* private fields */ }

A per-namespace monotonic sequencer.

Assigns strictly-increasing, gap-free u64 positions within each namespace, starting at 0. Namespaces are fully independent: assigning in one never affects another. The sequencer is pure in-memory state and holds no I/O — durability is the operator’s concern. After a restart the operator rebuilds state with Sequencer::resume_from (typically last_committed + 1), which refuses to rewind so monotonicity survives crashes.

use metamorphic_log::ingest::{Namespace, Sequencer};

let ns = Namespace::parse("acme").unwrap();
let mut seq = Sequencer::new();
assert_eq!(seq.next(&ns), 0);
assert_eq!(seq.next(&ns), 1);
assert_eq!(seq.peek(&ns), 2); // next position that would be assigned

Implementations

impl Sequencer

pub fn new() -> Self

Create an empty sequencer (every namespace starts at position 0).

pub fn peek(&self, namespace: &Namespace) -> u64

The next position that Sequencer::next would assign for namespace (without assigning it). A never-seen namespace peeks at 0.

pub fn next(&mut self, namespace: &Namespace) -> u64

Assign and return the next monotonic position for namespace.

Panics

Panics only on u64 position overflow (after 2^64 appends in a single namespace), which is not reachable in practice.

pub fn reserve( &mut self, namespace: &Namespace, count: u64, ) -> Result<Range<u64>>

Reserve a contiguous block of count positions for namespace, returning the half-open range [start, start + count). Useful for batch ingest: the operator assigns the whole batch in one step while preserving order and gap-freeness. A count of 0 returns an empty range at the current position and does not advance the counter.

Errors

Returns Error::SequenceOverflow if the block would overflow u64.

pub fn resume_from(&mut self, namespace: &Namespace, next: u64) -> Result<()>

Re-seat the next position for namespace from durable storage (e.g. on restart, to last_committed_position + 1).

This is monotonic-safe: it may only move the counter forward (or leave it unchanged). An attempt to set it below the current in-memory position is rejected rather than silently rewinding, because rewinding would re-issue an already-assigned position and break append-only ordering.

Errors

Returns Error::SequenceRegression if next is below the current position for namespace.

Trait Implementations

impl Clone for Sequencer

fn clone(&self) -> Sequencer

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Sequencer

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

Formats the value using the given formatter.

impl Default for Sequencer

fn default() -> Sequencer

Returns the “default value” for a type.