# Raft Engine Change Log

## [Unreleased]

## [0.4.2] - 2024-04-16

### Behavior Changes

* Periodically flush unsynced bytes when rewriting to avoid I/O jitters if flushing too many bytes impede the foreground writes. (#347)
* Errors will be returned if rewriting fails, instread of `panic` directly. (#343)

## [0.4.1] - 2023-09-14

### Behavior Changes

* When log recycling is enabled, Raft Engine will now retain 50% more log files to reduce the chance of running out.
* Reduce the scope of keys reserved for internal use.

## [0.4.0] - 2023-09-01

### Behavior Changes

* `LogBatch::put` returns a `Result<()>` instead of `()`. It errs when the key is reserved for internal use.
* Possible to specify a permission in `FileSystem::open`.
* Prometheus counter `raft_engine_log_file_count` no longer includes retired log files that are stashed for recycling. Those files are now tracked by a new counter `raft_engine_recycled_file_count`.

### Bug Fixes

* Fix data loss caused by aborted rewrite operation. Downgrading to an earlier version without the fix may produce phantom Raft Groups or keys, i.e. never written but appear in queries.
* Fix a potential bug that an un-persisted log batch is mistakenly recovered and causes checksum mismatch error when being read later.

### New Features

* Support preparing prefilled logs to enable log recycling when start-up. The amount of logs to prepare is controlled by `Config::prefill_limit`.
* Add a new configuration `spill-dir` to allow automatic placement of logs into an auxiliary directory when `dir` is full.
* Add a new method `Engine::fork` to duplicate an `Engine` to a new place, with a few disk file copies.
* Support configuring lz4 acceleration factor with `compression-level`.

## [0.3.0] - 2022-09-14

### Bug Fixes

* Unconditionally tolerate `fallocate` failures as a fix to its portability issue. Errors other than `EOPNOTSUPP` will still emit a warning.
* Avoid leaving fractured write after failure by reseeking the file writer. Panic if the reseek fails as well.
* Fix a parallel recovery panic bug.
* Fix panic when an empty batch is written to engine and then reused.

### New Features

* Add `PerfContext` which records detailed time breakdown of the write process to thread-local storage.
* Support recycling obsolete log files to reduce the cost of `fallocate`-ing new ones.

### Public API Changes

* Add `is_empty` to `Engine` API.
* Add metadata deletion capability to `FileSystem` trait. Users can implement `exists_metadata` and `delete_metadata` to clean up obsolete metadata from older versions of Raft Engine.
* Add `Engine::scan_messages` and `Engine::scan_raw_messages` for iterating over written key-values. 
* Add `Engine::get` for getting raw value.
* Move `sync` from `env::WriteExt` to `env::Handle`.
* Deprecate `bytes_per_sync`.

### Behavior Changes

* Change format version to 2 from 1 by default.
* Enable log recycling by default.

## [0.2.0] - 2022-05-25

### Bug Fixes

* Fix a false negative case of `LogBatch::is_empty()` #212
* Fix fsync ordering when rotating log file #219

### New Features

* Support limiting the memory usage of Raft Engine under new feature `swap` #211 
* Add a new Prometheus counter `raft_engine_memory_usage` to track memory usage #207

### Improvements

* Reduce memory usage by 25% #206

### Public API Changes

* Introduce a new error type `Full` #206
* `LogBatch::merge` returns a `Result<()>` instead of `()` #206