91166012c8
Summary: Previously, the flushes triggered by `WriteBufferManager` could affect the same CF repeatedly if it happens to get consecutive writes. Such flushes are not particularly useful for reducing memory usage since they switch nearly-empty memtables to immutable while they've just begun filling their first arena block. In fact they may not even reduce the mutable memory count if they involve replacing one mutable memtable containing one arena block with a new mutable memtable containing one arena block. Further, if such switches happen even a few times before a flush finishes, the immutable memtable limit will be reached and writes will stall. This PR adds a heuristic to not switch memtables to immutable for CFs that already have one or more immutable memtables awaiting flush. There is a memory usage regression if the user continues writing to the same CF, that DB does not have any CFs eligible for switching, flushes are not finishing, and the `WriteBufferManager` was constructed with `allow_stall=false`. Before, it would grow by switching nearly empty memtables until writes stall. Now, it would grow by filling memtables until writes stall. This feels like an acceptable behavior change because users who prefer to stall over violate the memory limit should be using `allow_stall=true`, which is unaffected by this PR. Pull Request resolved: https://github.com/facebook/rocksdb/pull/6364 Test Plan: - Command: `rm -rf /dev/shm/dbbench/ && TEST_TMPDIR=/dev/shm ./db_bench -benchmarks=fillrandom -num_multi_db=8 -num_column_families=2 -write_buffer_size=4194304 -db_write_buffer_size=16777216 -compression_type=none -statistics=true -target_file_size_base=4194304 -max_bytes_for_level_base=16777216` - `rocksdb.db.write.stall` count before this PR: 175 - `rocksdb.db.write.stall` count after this PR: 0 Reviewed By: jay-zhuang Differential Revision: D20167197 Pulled By: ajkr fbshipit-source-id: 4a64064e9bc33d57c0a35f15547542d0191d0cb7
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 especially suitable for storing multiple terabytes of data in a single database.
Start with example usage here: https://github.com/facebook/rocksdb/tree/main/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.
Questions and discussions are welcome on the RocksDB Developers Public Facebook group and email list on Google Groups.
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.