Struct CheckpointEntry 

pub struct CheckpointEntry {
    pub log_begin: u64,
    pub log_head: u64,
    pub log_read_only: u64,
    pub log_tail: u64,
    pub index_image_addr: u64,
    pub index_image_len: u64,
    pub key_count: u64,
    pub epoch: u32,
}

One shard’s position in its log, as of the last checkpoint.

Sixty four bytes, one cache line, which is not an accident: recovery reads every one of these and nothing else before it starts replaying.

Fields

log_begin: u64

The oldest address still in the file.

log_head: u64

The boundary between the stable region and the read only region.

log_read_only: u64

The boundary between the read only region and the mutable region.

log_tail: u64

Where the next append goes, and where replay starts.

index_image_addr: u64

Where the checkpointed index image lives.

index_image_len: u64

How long it is.

key_count: u64

Keys in this shard at the checkpoint, for INFO and for a sanity check after replay.

epoch: u32

The shard’s epoch at the checkpoint.

Implementations

impl CheckpointEntry

pub fn encode(&self, buf: &mut [u8])

Writes the entry and its checksum into 64 bytes.

Panics

If buf is not exactly CHECKPOINT_ENTRY_LEN bytes.

pub fn decode(buf: &[u8]) -> Result<CheckpointEntry>

Reads one entry back, checking its checksum and its ordering.

The ordering check is the useful one. Four addresses that are not monotonic describe a log with a negative sized region, and replaying from that produces a plausible looking database out of arbitrary bytes.

pub const fn addresses_are_ordered(&self) -> bool

begin <= head <= read_only <= tail, which 06 section 2 requires.

Trait Implementations

impl Clone for CheckpointEntry

fn clone(&self) -> CheckpointEntry

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for CheckpointEntry

impl Debug for CheckpointEntry

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

Formats the value using the given formatter.

impl Default for CheckpointEntry

fn default() -> CheckpointEntry

Returns the “default value” for a type.

impl Eq for CheckpointEntry

impl PartialEq for CheckpointEntry

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for CheckpointEntry