Struct Journal 

pub struct Journal<E: Storage + Metrics, A: CodecFixed> { /* private fields */ }

A segmented journal with fixed-size entries.

Each section is stored in a separate blob. Within each blob, items are fixed-size.

Repair

Like sqlite and rocksdb, the first invalid data read will be considered the new end of the journal (and the underlying Blob will be truncated to the last valid item). Repair occurs during init by checking each blob’s size.

Implementations

impl<E: Storage + Metrics, A: CodecFixedShared> Journal<E, A>

pub const CHUNK_SIZE: usize = A::SIZE

Size of each entry.

pub async fn init(context: E, cfg: Config) -> Result<Self, Error>

Initialize a new Journal instance.

All backing blobs are opened but not read during initialization. Use replay to iterate over all items.

pub async fn append(&mut self, section: u64, item: A) -> Result<u64, Error>

Append a new item to the journal in the given section.

Returns the position of the item within the section (0-indexed).

pub async fn get(&self, section: u64, position: u64) -> Result<A, Error>

Read the item at the given section and position.

Errors

• Error::AlreadyPrunedToSection if the section has been pruned.
• Error::SectionOutOfRange if the section doesn’t exist.
• Error::ItemOutOfRange if the position is beyond the blob size.

pub async fn last(&self, section: u64) -> Result<Option<A>, Error>

Read the last item in a section, if any.

pub async fn replay( &self, start_section: u64, start_position: u64, buffer: NonZeroUsize, ) -> Result<impl Stream<Item = Result<(u64, u64, A), Error>> + Send + '_, Error>

Returns a stream of all items starting from the given section.

Each item is returned as (section, position, item).

pub async fn sync(&self, section: u64) -> Result<(), Error>

Sync the given section to storage.

pub async fn sync_all(&self) -> Result<(), Error>

Sync all sections to storage.

pub async fn prune(&mut self, min: u64) -> Result<bool, Error>

Prune all sections less than min. Returns true if any were pruned.

pub fn oldest_section(&self) -> Option<u64>

Returns the oldest section number, if any blobs exist.

pub fn newest_section(&self) -> Option<u64>

Returns the newest section number, if any blobs exist.

pub fn sections(&self) -> impl Iterator<Item = u64> + '_

Returns an iterator over all section numbers.

pub async fn section_len(&self, section: u64) -> Result<u64, Error>

Returns the number of items in the given section.

pub async fn size(&self, section: u64) -> Result<u64, Error>

Returns the byte size of the given section.

pub async fn rewind(&mut self, section: u64, offset: u64) -> Result<(), Error>

Rewind the journal to a specific section and byte offset.

This truncates the section to the given size. All sections after section are removed.

pub async fn rewind_section( &mut self, section: u64, size: u64, ) -> Result<(), Error>

Rewind only the given section to a specific byte offset.

Unlike rewind, this does not affect other sections.

pub async fn destroy(self) -> Result<(), Error>

Remove all underlying blobs.