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RocksDB v6.19.0 Release Notes

Release Date: 2021-03-21 // about 3 years ago

  • 🐛 Bug Fixes

    • 🛠 Fixed the truncation error found in APIs/tools when dumping block-based SST files in a human-readable format. After fix, the block-based table can be fully dumped as a readable file.
    • When hitting a write slowdown condition, no write delay (previously 1 millisecond) is imposed until delayed_write_rate is actually exceeded, with an initial burst allowance of 1 millisecond worth of bytes. Also, beyond the initial burst allowance, delayed_write_rate is now more strictly enforced, especially with multiple column families.

    Public API change

    • Changed default BackupableDBOptions::share_files_with_checksum to true and deprecated false because of potential for data loss. Note that accepting this change in behavior can temporarily increase backup data usage because files are not shared between backups using the two different settings. Also removed obsolete option kFlagMatchInterimNaming.
    • Add a new option BlockBasedTableOptions::max_auto_readahead_size. RocksDB does auto-readahead for iterators on noticing more than two reads for a table file if user doesn't provide readahead_size. The readahead starts at 8KB and doubles on every additional read upto max_auto_readahead_size and now max_auto_readahead_size can be configured dynamically as well. Found that 256 KB readahead size provides the best performance, based on experiments, for auto readahead. Experiment data is in PR #3282. If value is set 0 then no automatic prefetching will be done by rocksdb. Also changing the value will only affect files opened after the change.
    • ➕ Add suppport to extend DB::VerifyFileChecksums API to also verify blob files checksum.
    • When using the new BlobDB, the amount of data written by flushes/compactions is now broken down into table files and blob files in the compaction statistics; namely, Write(GB) denotes the amount of data written to table files, while Wblob(GB) means the amount of data written to blob files.
    • 🆕 New default BlockBasedTableOptions::format_version=5 to enable new Bloom filter implementation by default, compatible with RocksDB versions >= 6.6.0.
    • ➕ Add new SetBufferSize API to WriteBufferManager to allow dynamic management of memory allotted to all write buffers. This allows user code to adjust memory monitoring provided by WriteBufferManager as process memory needs change datasets grow and shrink.
    • Clarified the required semantics of Read() functions in FileSystem and Env APIs. Please ensure any custom implementations are compliant.
    • For the new integrated BlobDB implementation, compaction statistics now include the amount of data read from blob files during compaction (due to garbage collection or compaction filters). Write amplification metrics have also been extended to account for data read from blob files.
    • ➕ Add EqualWithoutTimestamp() to Comparator.
    • ⏱ Extend support to track blob files in SSTFileManager whenever a blob file is created/deleted. Blob files will be scheduled to delete via SSTFileManager and SStFileManager will now take blob files in account while calculating size and space limits along with SST files.
    • ➕ Add new Append and PositionedAppend API with checksum handoff to legacy Env.

    🆕 New Features

    • 👌 Support compaction filters for the new implementation of BlobDB. Add FilterBlobByKey() to CompactionFilter. Subclasses can override this method so that compaction filters can determine whether the actual blob value has to be read during compaction. Use a new kUndetermined in CompactionFilter::Decision to indicated that further action is necessary for compaction filter to make a decision.
    • ➕ Add support to extend retrieval of checksums for blob files from the MANIFEST when checkpointing. During backup, rocksdb can detect corruption in blob files during file copies.
    • ➕ Add new options for db_bench --benchmarks: flush, waitforcompaction, compact0, compact1.
    • ➕ Add an option to BackupEngine::GetBackupInfo to include the name and size of each backed-up file. Especially in the presence of file sharing among backups, this offers detailed insight into backup space usage.
    • Enable backward iteration on keys with user-defined timestamps.
    • ➕ Add statistics and info log for error handler: counters for bg error, bg io error, bg retryable io error, auto resume count, auto resume total retry number, and auto resume sucess; Histogram for auto resume retry count in each recovery call. Note that, each auto resume attempt will have one or multiple retries.

    Behavior Changes

    • 🔀 During flush, only WAL sync retryable IO error is mapped to hard error, which will stall the writes. When WAL is used but only SST file write has retryable IO error, it will be mapped to soft error and write will not be affected.