d5a46c40e5
Summary: If the block Cache is full with strict_capacity_limit=false, then our CacheEntryStatsCollector could be immediately evicted on release, so iterating through column families with shared block cache could trigger re-scan for each CF. This change fixes that problem by pinning the CacheEntryStatsCollector from InternalStats so that it's not evicted. I had originally thought that this object could participate in LRU like everything else, but even though a re-load+re-scan only touches memory, it can be orders of magnitude more expensive than other cache misses. One service in Facebook has scans that take ~20s over 100GB block cache that is mostly 4KB entries. (The up-side of this bug and https://github.com/facebook/rocksdb/issues/8369 is that we had a natural experiment on the effect on some service metrics even with block cache scans running continuously in the background--a kind of worst case scenario. Metrics like latency were not affected enough to trigger warnings.) Other smaller fixes: 20s is already a sizable portion of 600s stats dump period, or 180s default max age to force re-scan, so added logic to ensure that (for each block cache) we don't spend more than 0.2% of our background thread time scanning it. Nevertheless, "foreground" requests for cache entry stats (calls to `db->GetMapProperty(DB::Properties::kBlockCacheEntryStats)`) are permitted to consume more CPU. Renamed field to cache_entry_stats_ to match code style. This change is intended for patching in 6.21 release. Pull Request resolved: https://github.com/facebook/rocksdb/pull/8385 Test Plan: unit test expanded to cover new logic (detect regression), some manual testing with db_bench Reviewed By: ajkr Differential Revision: D29042759 Pulled By: pdillinger fbshipit-source-id: 236faa902397f50038c618f50fbc8cf3f277308c |
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README.md
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/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/ and https://rocksdb.slack.com/
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.