Rocksdb Change Log

Unreleased (will be released with 3.2.0)

It makes more sense for spinning disk workloads, while RocksDB is primarily designed for flash and memory,
It added some complexity to the important code-paths,
None of our internal customers were really using it. Because of that, Options::disable_seek_compaction is now obsolete. It is still a parameter in Options, so it does not break the build, but it does not have any effect. We plan to completely remove it at some point, so we ask users to please remove this option from your code base.

Replaced ColumnFamilyOptions::table_properties_collectors with ColumnFamilyOptions::table_properties_collector_factories
Add two paramters to NewHashLinkListRepFactory() for logging on too many entries in a hash bucket when flushing.

Hash index for block-based table will be materialized and reconstructed more efficiently. Previously hash index is constructed by scanning the whole table during every table open.
FIFO compaction style
Add AdaptiveTableFactory, which is used to convert from a DB of PlainTable to BlockBasedTabe, or vise versa. It can be created using NewAdaptiveTableFactory()

Added _LEVEL to all InfoLogLevel enums
Deprecated ReadOptions.prefix and ReadOptions.prefix_seek. Seek() defaults to prefix-based seek when Options.prefix_extractor is supplied. More detail is documented in https://github.com/facebook/rocksdb/wiki/Prefix-Seek-API-Changes
MemTableRepFactory::CreateMemTableRep() takes info logger as an extra parameter.

Removed arena.h from public header files.
By default, checksums are verified on every read from database
Change default value of several options, including: paranoid_checks=true, max_open_files=5000, level0_slowdown_writes_trigger=20, level0_stop_writes_trigger=24, disable_seek_compaction=true, max_background_flushes=1 and allow_mmap_writes=false
Added is_manual_compaction to CompactionFilter::Context
Added "virtual void WaitForJoin()" in class Env. Default operation is no-op.
Removed BackupEngine::DeleteBackupsNewerThan() function
Added new option -- verify_checksums_in_compaction
Changed Options.prefix_extractor from raw pointer to shared_ptr (take ownership) Changed HashSkipListRepFactory and HashLinkListRepFactory constructor to not take SliceTransform object (use Options.prefix_extractor implicitly)
Added Env::GetThreadPoolQueueLen(), which returns the waiting queue length of thread pools
Added a command "checkconsistency" in ldb tool, which checks if file system state matches DB state (file existence and file sizes)
Separate options related to block based table to a new struct BlockBasedTableOptions.
WriteBatch has a new function Count() to return total size in the batch, and Data() now returns a reference instead of a copy
Add more counters to perf context.
Supports several more DB properties: compaction-pending, background-errors and cur-size-active-mem-table.

If we find one truncated record at the end of the MANIFEST or WAL files, we will ignore it. We assume that writers of these records were interrupted and that we can safely ignore it.
A new SST format "PlainTable" is added, which is optimized for memory-only workloads. It can be created through NewPlainTableFactory() or NewTotalOrderPlainTableFactory().
A new mem table implementation hash linked list optimizing for the case that there are only few keys for each prefix, which can be created through NewHashLinkListRepFactory().
Merge operator supports a new function PartialMergeMulti() to allow users to do partial merges against multiple operands.
Now compaction filter has a V2 interface. It buffers the kv-pairs sharing the same key prefix, process them in batches, and return the batched results back to DB. The new interface uses a new structure CompactionFilterContext for the same purpose as CompactionFilter::Context in V1.
Geo-spatial support for locations and radial-search.

Renamed StackableDB::GetRawDB() to StackableDB::GetBaseDB().
Renamed WriteBatch::Data() const std::string& Data() const.
Renamed class TableStats to TableProperties.
Deleted class PrefixHashRepFactory. Please use NewHashSkipListRepFactory() instead.
Supported multi-threaded EnableFileDeletions() and DisableFileDeletions().
Added DB::GetOptions().
Added DB::GetDbIdentity().

Added BackupableDB
Implemented TailingIterator, a special type of iterator that doesn't create a snapshot (can be used to read newly inserted data) and is optimized for doing sequential reads.
Added property block for table, which allows (1) a table to store its metadata and (2) end user to collect and store properties they are interested in.
Enabled caching index and filter block in block cache (turned off by default).
Supported error report when doing manual compaction.
Supported additional Linux platform flavors and Mac OS.
Put with SliceParts - Variant of Put() that gathers output like writev(2)
Bug fixes and code refactor for compatibility with upcoming Column Family feature.

Huge benchmark performance improvements by multiple efforts. For example, increase in readonly QPS from about 530k in 2.6 release to 1.1 million in 2.7 [1]
Speeding up a way RocksDB deleted obsolete files - no longer listing the whole directory under a lock -- decrease in p99
Use raw pointer instead of shared pointer for statistics: 5b825d -- huge increase in performance -- shared pointers are slow
Optimized locking for Get() -- 1fdb3f -- 1.5x QPS increase for some workloads
Cache speedup - e8d40c3
Implemented autovector, which allocates first N elements on stack. Most of vectors in RocksDB are small. Also, we never want to allocate heap objects while holding a mutex. -- c01676e4
Lots of efforts to move malloc, memcpy and IO outside of locks