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RocksDB v7.5.0 Release Notes

  • 🆕 New Features

    • Mempurge option flag experimental_mempurge_threshold is now a ColumnFamilyOptions and can now be dynamically configured using SetOptions().
    • Support backward iteration when ReadOptions::iter_start_ts is set.
    • Provide support for ReadOptions.async_io with direct_io to improve Seek latency by using async IO to parallelize child iterator seek and doing asynchronous prefetching on sequential scans.
    • ➕ Added support for blob caching in order to cache frequently used blobs for BlobDB.
      • User can configure the new ColumnFamilyOptions blob_cache to enable/disable blob caching.
      • Either sharing the backend cache with the block cache or using a completely separate cache is supported.
      • A new abstraction interface called BlobSource for blob read logic gives all users access to blobs, whether they are in the blob cache, secondary cache, or (remote) storage. Blobs can be potentially read both while handling user reads (Get, MultiGet, or iterator) and during compaction (while dealing with compaction filters, Merges, or garbage collection) but eventually all blob reads go through Version::GetBlob or, for MultiGet, Version::MultiGetBlob (and then get dispatched to the interface -- BlobSource).
    • Add experimental tiered compaction feature AdvancedColumnFamilyOptions::preclude_last_level_data_seconds, which makes sure the new data inserted within preclude_last_level_data_seconds won't be placed on cold tier (the feature is not complete).

    Public API changes

    • ➕ Add metadata related structs and functions in C API, including
      • rocksdb_get_column_family_metadata() and rocksdb_get_column_family_metadata_cf() to obtain rocksdb_column_family_metadata_t.
      • rocksdb_column_family_metadata_t and its get functions & destroy function.
      • rocksdb_level_metadata_t and its and its get functions & destroy function.
      • rocksdb_file_metadata_t and its and get functions & destroy functions.
    • Add suggest_compact_range() and suggest_compact_range_cf() to C API.
    • When using block cache strict capacity limit (LRUCache with strict_capacity_limit=true), DB operations now fail with Status code kAborted subcode kMemoryLimit (IsMemoryLimit()) instead of kIncomplete (IsIncomplete()) when the capacity limit is reached, because Incomplete can mean other specific things for some operations. In more detail, Cache::Insert() now returns the updated Status code and this usually propagates through RocksDB to the user on failure.
    • 🆕 NewClockCache calls temporarily return an LRUCache (with similar characteristics as the desired ClockCache). This is because ClockCache is being replaced by a new version (the old one had unknown bugs) but this is still under development.
    • Add two functions int ReserveThreads(int threads_to_be_reserved) and int ReleaseThreads(threads_to_be_released) into Env class. In the default implementation, both return 0. Newly added xxxEnv class that inherits Env should implement these two functions for thread reservation/releasing features.
    • Add rocksdb_options_get_prepopulate_blob_cache and rocksdb_options_set_prepopulate_blob_cache to C API.
    • ➕ Add prepopulateBlobCache and setPrepopulateBlobCache to Java API.

    🐛 Bug Fixes

    • 🛠 Fix a bug in which backup/checkpoint can include a WAL deleted by RocksDB.
    • 🛠 Fix a bug where concurrent compactions might cause unnecessary further write stalling. In some cases, this might cause write rate to drop to minimum.
    • 🌲 Fix a bug in Logger where if dbname and db_log_dir are on different filesystems, dbname creation would fail wrt to db_log_dir path returning an error and fails to open the DB.
    • 🛠 Fix a CPU and memory efficiency issue introduce by https://github.com/facebook/rocksdb/pull/8336 which made InternalKeyComparator configurable as an unintended side effect.