Struct StateChangelogEntry 

pub struct StateChangelogEntry {
    pub epoch: u64,
    pub key_hash: u64,
    pub mmap_offset: u64,
    pub value_len: u32,
    /* private fields */
}

Zero-allocation changelog entry for Ring 0 hot path.

This struct is designed for minimal memory footprint (32 bytes) and cache-efficient access. It stores offset references into the mmap state store rather than copying key/value data.

Memory Layout

The struct is repr(C) to ensure predictable memory layout:

• epoch: 8 bytes - Logical epoch number for ordering
• key_hash: 8 bytes - FxHash of the key for quick comparison
• mmap_offset: 8 bytes - Offset into the mmap state store
• value_len: 4 bytes - Length of the value (0 for deletes)
• op: 1 byte - Operation type (Put/Delete)
• _padding: 3 bytes - Alignment padding

Fields

epoch: u64

Logical epoch number for ordering changelog entries.

key_hash: u64

FxHash of the key (for deduplication and lookup).

mmap_offset: u64

Offset into the mmap state store where value is stored.

value_len: u32

Length of the value in bytes (0 for Delete operations).

Implementations

impl StateChangelogEntry

pub fn put(epoch: u64, key_hash: u64, mmap_offset: u64, value_len: u32) -> Self

Creates a new Put changelog entry.

pub fn delete(epoch: u64, key_hash: u64) -> Self

Creates a new Delete changelog entry.

pub fn from_key( key: &[u8], epoch: u64, mmap_offset: u64, value_len: u32, op: StateOp, ) -> Self

Creates a changelog entry from a key with automatic hashing.

pub fn op(&self) -> StateOp

Returns the operation type.

pub fn is_put(&self) -> bool

Returns true if this is a Put operation.

pub fn is_delete(&self) -> bool

Returns true if this is a Delete operation.

pub fn hash_key(key: &[u8]) -> u64

Hash a key using FxHash (fast, consistent across entries).

Trait Implementations

impl Clone for StateChangelogEntry

fn clone(&self) -> StateChangelogEntry

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for StateChangelogEntry

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

Formats the value using the given formatter.

impl Copy for StateChangelogEntry