rocksdb/HISTORY.md

# Rocksdb Change Log

## Unreleased (will be released in 3.0)
* By default, max_background_flushes is 1 and flush process is
  removed from background compaction process. Flush process is now always
  executed in high priority thread pool.

## Unreleased (will be relased in 2.8)
## Unreleased

### Public API changes

* Removed arena.h from public header files.
* By default, checksums are verified on every read from database

## 2.7.0 (01/28/2014)

### Public API changes

* Renamed `StackableDB::GetRawDB()` to `StackableDB::GetBaseDB()`.
* Renamed `WriteBatch::Data()` `const std::string& Data() const`.
* Renamed class `TableStats` to `TableProperties`.
* Deleted class `PrefixHashRepFactory`. Please use `NewHashSkipListRepFactory()` instead.
* Supported multi-threaded `EnableFileDeletions()` and `DisableFileDeletions()`.
* Added `DB::GetOptions()`.
* Added `DB::GetDbIdentity()`.

### New Features

* Added [BackupableDB](https://github.com/facebook/rocksdb/wiki/How-to-backup-RocksDB%3F)
* Implemented [TailingIterator](https://github.com/facebook/rocksdb/wiki/Tailing-Iterator), a special type of iterator that
  doesn't create a snapshot (can be used to read newly inserted data)
  and is optimized for doing sequential reads.
* Added property block for table, which allows (1) a table to store
  its metadata and (2) end user to collect and store properties they
  are interested in.
* Enabled caching index and filter block in block cache (turned off by default).
* Supported error report when doing manual compaction.
* Supported additional Linux platform flavors and Mac OS.
* Put with `SliceParts` - Variant of `Put()` that gathers output like `writev(2)`
* Bug fixes and code refactor for compatibility with upcoming Column
  Family feature.

### Performance Improvements

* Huge benchmark performance improvements by multiple efforts. For example, increase in readonly QPS from about 530k in 2.6 release to 1.1 million in 2.7 [1]
* Speeding up a way RocksDB deleted obsolete files - no longer listing the whole directory under a lock -- decrease in p99
* Use raw pointer instead of shared pointer for statistics: [5b825d](https://github.com/facebook/rocksdb/commit/5b825d6964e26ec3b4bb6faa708ebb1787f1d7bd) -- huge increase in performance -- shared pointers are slow
* Optimized locking for `Get()` -- [1fdb3f](https://github.com/facebook/rocksdb/commit/1fdb3f7dc60e96394e3e5b69a46ede5d67fb976c) -- 1.5x QPS increase for some workloads
* Cache speedup - [e8d40c3](https://github.com/facebook/rocksdb/commit/e8d40c31b3cca0c3e1ae9abe9b9003b1288026a9)
* Implemented autovector, which allocates first N elements on stack. Most of vectors in RocksDB are small. Also, we never want to allocate heap objects while holding a mutex. -- [c01676e4](https://github.com/facebook/rocksdb/commit/c01676e46d3be08c3c140361ef1f5884f47d3b3c)
* Lots of efforts to move malloc, memcpy and IO outside of locks