Struct Journal 

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

Implementation of Journal storage.

Implementations

impl<E: Storage + Metrics, A: CodecFixed<Cfg = ()>> Journal<E, A>

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. The replay method can be used to iterate over all items in the Journal.

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).

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

Sync any pending updates to disk.

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

Return the total number of items in the journal, irrespective of pruning. The next value appended to the journal will be at this position.

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

Append a new item to the journal. Return the item’s position in the journal, or error if the operation fails.

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

Rewind the journal to the given size. Returns Error::MissingBlob if the rewind point precedes the oldest retained element point. The journal is not synced after rewinding.

Warnings

• This operation is not guaranteed to survive restarts until sync is called.
• This operation is not atomic, but it will always leave the journal in a consistent state in the event of failure since blobs are always removed from newest to oldest.

pub async fn oldest_retained_pos(&self) -> Result<Option<u64>, Error>

Return the position of the oldest item in the journal that remains readable.

Note that this value could be older than the min_item_pos last passed to prune.

pub async fn read(&self, pos: u64) -> Result<A, Error>

Read the item at position pos in the journal.

Errors

• Error::ItemPruned if the item at position pos is pruned.
• Error::ItemOutOfRange if the item at position pos does not exist.

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

Returns an ordered stream of all items in the journal with position >= start_pos.

Panics

Panics start_pos exceeds log size.

Integrity

If any corrupted data is found, the stream will return an error.

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

Allow the journal to prune items older than min_item_pos. The journal may not prune all such items in order to preserve blob boundaries, but the amount of such items will always be less than the configured number of items per blob. Returns true if any items were pruned.

Note that this operation may NOT be atomic, however it’s guaranteed not to leave gaps in the event of failure as items are always pruned in order from oldest to newest.

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

Syncs and closes all open sections.

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

Remove any underlying blobs created by the journal.