b7198c3afe
Summary: This diff allows a Writer to join the next write batch group without acquiring any locks. Waiting is performed via a per-Writer mutex, so all of the non-leader writers never need to acquire the db mutex. It is now possible to join a write batch group after the leader has been chosen but before the batch has been constructed. This diff doesn't increase parallelism, but reduces synchronization overheads. For some CPU-bound workloads (no WAL, RAM-sized working set) this can substantially reduce contention on the db mutex in a multi-threaded environment. With T=8 N=500000 in a CPU-bound scenario (see the test plan) this is good for a 33% perf win. Not all scenarios see such a win, but none show a loss. This code is slightly faster even for the single-threaded case (about 2% for the CPU-bound scenario below). Test Plan: 1. unit tests 2. COMPILE_WITH_TSAN=1 make check 3. stress high-contention scenarios with db_bench -benchmarks=fillrandom -threads=$T -batch_size=1 -memtablerep=skip_list -value_size=0 --num=$N -level0_slowdown_writes_trigger=9999 -level0_stop_writes_trigger=9999 -disable_auto_compactions --max_write_buffer_number=8 -max_background_flushes=8 --disable_wal --write_buffer_size=160000000 Reviewers: sdong, igor, rven, ljin, yhchiang Subscribers: dhruba Differential Revision: https://reviews.facebook.net/D43887
RocksDB: A Persistent Key-Value Store for Flash and RAM Storage
RocksDB is developed and maintained by Facebook Database Engineering Team. It is built on earlier work on LevelDB by Sanjay Ghemawat (sanjay@google.com) and Jeff Dean (jeff@google.com)
This code is a library that forms the core building block for a fast key value server, especially suited for storing data on flash drives. It has a Log-Structured-Merge-Database (LSM) design with flexible tradeoffs between Write-Amplification-Factor (WAF), Read-Amplification-Factor (RAF) and Space-Amplification-Factor (SAF). It has multi-threaded compactions, making it specially suitable for storing multiple terabytes of data in a single database.
Start with example usage here: https://github.com/facebook/rocksdb/tree/master/examples
See the github wiki for more explanation.
The public interface is in include/. Callers should not include or
rely on the details of any other header files in this package. Those
internal APIs may be changed without warning.
Design discussions are conducted in https://www.facebook.com/groups/rocksdb.dev/