A library that provides an embeddable, persistent key-value store for fast storage.
43890774ed
Summary: There is a race condition if WAL tracking in the MANIFEST is enabled in a database that disables 2PC. The race condition is between two background flush threads trying to install flush results to the MANIFEST. Consider an example database with two column families: "default" (cfd0) and "cf1" (cfd1). Initially, both column families have one mutable (active) memtable whose data backed by 6.log. 1. Trigger a manual flush for "cf1", creating a 7.log 2. Insert another key to "default", and trigger flush for "default", creating 8.log 3. BgFlushThread1 finishes writing 9.sst 4. BgFlushThread2 finishes writing 10.sst ``` Time BgFlushThread1 BgFlushThread2 | mutex_.Lock() | precompute min_wal_to_keep as 6 | mutex_.Unlock() | mutex_.Lock() | precompute min_wal_to_keep as 6 | join MANIFEST write queue and mutex_.Unlock() | write to MANIFEST | mutex_.Lock() | cfd1->log_number = 7 | Signal bg_flush_2 and mutex_.Unlock() | wake up and mutex_.Lock() | cfd0->log_number = 8 | FindObsoleteFiles() with job_context->log_number == 7 | mutex_.Unlock() | PurgeObsoleteFiles() deletes 6.log V ``` As shown in the above, BgFlushThread2 thinks that the min wal to keep is 6.log because "cf1" has unflushed data in 6.log (cf1.log_number=6). Similarly, BgThread1 thinks that min wal to keep is also 6.log because "default" has unflushed data (default.log_number=6). No WAL deletion will be written to MANIFEST because 6 is equal to `versions_->wals_.min_wal_number_to_keep`, due to https://github.com/facebook/rocksdb/blob/7.1.fb/db/memtable_list.cc#L513:L514. The bg flush thread that finishes last will perform file purging. `job_context.log_number` will be evaluated as 7, i.e. the min wal that contains unflushed data, causing 6.log to be deleted. However, MANIFEST thinks 6.log should still exist. If you close the db at this point, you won't be able to re-open it if `track_and_verify_wal_in_manifest` is true. We must handle the case of multiple bg flush threads, and it is difficult for one bg flush thread to know the correct min wal number until the other bg flush threads have finished committing to the manifest and updated the `cfd::log_number`. To fix this issue, we rename an existing variable `min_log_number_to_keep_2pc` to `min_log_number_to_keep`, and use it to track WAL file deletion in non-2pc mode as well. This variable is updated only 1) during recovery with mutex held, or 2) in the MANIFEST write thread. `min_log_number_to_keep` means RocksDB will delete WALs below it, although there may be WALs above it which are also obsolete. Formally, we will have [min_wal_to_keep, max_obsolete_wal]. During recovery, we make sure that only WALs above max_obsolete_wal are checked and added back to `alive_log_files_`. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9715 Test Plan: ``` make check ``` Also ran stress test below (with asan) to make sure it completes successfully. ``` TEST_TMPDIR=/dev/shm/rocksdb OPT=-g ASAN_OPTIONS=disable_coredump=0 \ CRASH_TEST_EXT_ARGS=--compression_type=zstd SKIP_FORMAT_BUCK_CHECKS=1 \ make J=52 -j52 blackbox_asan_crash_test ``` Reviewed By: ltamasi Differential Revision: D34984412 Pulled By: riversand963 fbshipit-source-id: c7b21a8d84751bb55ea79c9f387103d21b231005 |
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| DEFAULT_OPTIONS_HISTORY.md | ||
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| LICENSE.Apache | ||
| LICENSE.leveldb | ||
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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.