Enum AckPolicy 

pub enum AckPolicy {
    Disk,
    Ram,
    DiskAndRam,
    TwoDisks,
}

Operator-facing ack policy: which copies of an event must exist before its response is released. Each variant maps to a named Clause list composed directly in code. See docs/replication.md for the menu in operational terms.

clap::ValueEnum derives --ack-policy <disk|ram|disk+ram|two-disks>; the disk+ram spelling is set explicitly because the derive would kebab-case the variant to disk-and-ram.

Variants

Disk

persisted>=1. One fsynced copy, on whichever node’s disk confirms first. Required when running with --standalone; appropriate for dev/staging deployments without a replica.

Ram

in_memory>=2. Two nodes hold the event in memory before the client ack; every disk write trails asynchronously off the ack path (the journal still fsyncs every batch, it just no longer gates responses). Survives any single node failure via failover; loses only the un-fsynced tail on a simultaneous whole-cluster power loss. For deployments where fsync is slow (cloud block storage) or where that bounded RPO is an acceptable trade for the lowest ack latency. Fails closed when no replica is connected.

DiskAndRam

persisted>=1 && in_memory>=2. One fsynced copy plus a second copy in another node’s memory. Single-failure-safe with a brief RAM-only window (~80 µs on PLP-backed NVMe) for the second copy. The default — typical live deployments. Faster than TwoDisks: an acknowledgement waits for the second node to receive the event, not to fsync it. Fails closed when no replica is connected.

TwoDisks

persisted>=2. Two fsynced copies before the client ack. Zero RAM-only window; the gate stalls if no replica is currently connected. Compliance-driven deployments.

Implementations

impl AckPolicy

pub fn as_str(self) -> &'static str

CLI / log-friendly name. Matches the clap::ValueEnum spelling.

pub fn parse(s: &str) -> Option<Self>

Parse the admin-channel / CLI wire spelling. Accepts exactly the strings as_str emits so operators only have to learn one vocabulary across --ack-policy and the admin ACK-POLICY command.

pub fn parse_legacy(s: &str) -> Option<Self>

Parse the pre-0.15 “durability mode” names, for the deprecated DURABILITY admin alias. Accepts the current spellings too so the alias is a strict superset of parse. Removed with the alias in the next minor release.

pub fn as_u8(self) -> u8

Stable u8 discriminant: the byte a journaled AckPolicyChange carries (to_byte), and the one the health gauges export.

These values are a wire format, not just an in-process ABI: they are in every journal holding a policy change, streamed to every replica with the entries, and a replica decodes the one its lineage holds with from_byte to judge auto-promotion (see raft_promotion). So they must stay stable across releases in two directions — the round-trip from_u8(as_u8(x)) == Some(x) has to hold, and a value once released can never be reassigned to a different policy, or a peer on an older build would silently read the new policy as the old one. Add new policies on the next free byte; never renumber. (The bytes predate the current names: they were assigned to local/hybrid/durably-replicated/replicated and kept through the rename.)

A peer that does not know a byte gets None and refuses to auto-promote on it — fail-closed, and the reason replicas must be upgraded before a primary starts journaling a new policy.

pub fn from_u8(b: u8) -> Option<Self>

Inverse of as_u8. Returns None for an unknown byte — one a newer build wrote, or a bug. A primary refuses to start on a lineage holding one; the response stage, meeting one in a change it journaled itself, logs and retains the prior policy rather than silently falling back.

Trait Implementations

impl Clone for AckPolicy

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for AckPolicy

impl Debug for AckPolicy

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

Formats the value using the given formatter.

impl Display for AckPolicy

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

Formats the value using the given formatter.

impl Eq for AckPolicy

impl PartialEq for AckPolicy

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for AckPolicy

impl ValueEnum for AckPolicy

fn value_variants<'a>() -> &'a [Self]

All possible argument values, in display order.

fn to_possible_value<'a>(&self) -> Option<PossibleValue>

The canonical argument value.

fn from_str(input: &str, ignore_case: bool) -> Result<Self, String>

Parse an argument into Self.