de76909464
Summary: Savepoints are assumed to be used in a stack-wise fashion (only the top element should be used), so they were stored by `WriteBatch` in a member variable `save_points` using an std::stack. Conceptually this is fine, but the implementation had a few issues: - the `save_points_` instance variable was a plain pointer to a heap- allocated `SavePoints` struct. The destructor of `WriteBatch` simply deletes this pointer. However, the copy constructor of WriteBatch just copied that pointer, meaning that copying a WriteBatch with active savepoints will very likely have crashed before. Now a proper copy of the savepoints is made in the copy constructor, and not just a copy of the pointer - `save_points_` was an std::stack, which defaults to `std::deque` for the underlying container. A deque is a bit over the top here, as we only need access to the most recent savepoint (i.e. stack.top()) but never any elements at the front. std::deque is rather expensive to initialize in common environments. For example, the STL implementation shipped with GNU g++ will perform a heap allocation of more than 500 bytes to create an empty deque object. Although the `save_points_` container is created lazily by RocksDB, moving from a deque to a plain `std::vector` is much more memory-efficient. So `save_points_` is now a vector. - `save_points_` was changed from a plain pointer to an `std::unique_ptr`, making ownership more explicit. Pull Request resolved: https://github.com/facebook/rocksdb/pull/5192 Differential Revision: D15024074 Pulled By: maysamyabandeh fbshipit-source-id: 5b128786d3789cde94e46465c9e91badd07a25d7
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/
License
RocksDB is dual-licensed under both the GPLv2 (found in the COPYING file in the root directory) and Apache 2.0 License (found in the LICENSE.Apache file in the root directory). You may select, at your option, one of the above-listed licenses.