Struct RankedRegister

pub struct RankedRegister { /* private fields */ }

A ranked register backed by FoundationDB

Provides a mutable register with conflict detection via ranks. No initialization is needed — an absent key represents the bottom state (zero ranks, no value).

Thread Safety

RankedRegister is Clone, Send, and Sync. It holds only a Subspace and can be safely shared across tasks.

Implementations

impl RankedRegister

pub fn new(subspace: Subspace) -> Self

Create a new ranked register instance

The subspace isolates this register from other data in the database. No initialization step is required — the register starts in the bottom state (zero ranks, no value) until the first write.

pub fn with_max_value_bytes(subspace: Subspace, limit: usize) -> Self

Create a ranked register with a local aggregate value-size limit.

The limit applies only to writes through this handle. It is not durable state, so use compatible limits for all writers of the same subspace.

pub fn subspace(&self) -> &Subspace

Returns a reference to the underlying subspace

pub async fn read<T>(&self, txn: &T, rank: Rank) -> Result<ReadResult>

where T: Deref<Target = Transaction>,

Perform a ranked read

Raises max_read_rank only when the given rank is higher, installing a fence that prevents lower-ranked writes. A superseded rank returns the current write rank and value without changing the installed fence.

Used by the leader before writing to ensure consistency.

pub async fn write<T>( &self, txn: &T, rank: Rank, value: &[u8], ) -> Result<WriteResult>

where T: Deref<Target = Transaction>,

Perform a ranked write

Commits the value only if:

• rank >= max_read_rank (no higher fence)
• rank > max_write_rank (no equal-or-higher write)

Returns WriteResult::Committed or WriteResult::Aborted. Returns RankedRegisterError::ValueTooLarge when this handle has a configured limit and value exceeds it.

pub async fn value<T>(&self, txn: &T) -> Result<Option<Vec<u8>>>

where T: Deref<Target = Transaction>,

Read the current value without updating ranks

Safe for followers and observers: it installs no durable fence. Its normal non-snapshot FoundationDB read still adds a conflict range for this register key, so it can conflict with a concurrent leader write.

Trait Implementations

impl Clone for RankedRegister

fn clone(&self) -> RankedRegister

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for RankedRegister

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

Formats the value using the given formatter.