Log Message:
leveldb: updated to 1.23

1.23

Sync MANIFEST before closing in db_impl when creating a new DB. Add logging with \ 
debugging information when failing to load a version set.
Optimize leveldb block seeks to utilize the current iterator location. This is \ 
beneficial when iterators are reused and seeks are not random but increasing. It \ 
is additionally beneficial with larger block sizes and keys with common \ 
prefixes.
Documentation fixes
(cmumford/printf-fix) Fixed fprintf of 64-bit value.
(cmumford/benchmark) Added google/benchmark submodule.
Internal test cleanup
Internal cleanup migrating StatusOr.
avoid unnecessary memory copy
Fix accidental double std:: qualifiers.
Add some std:: qualifiers to types and functions.
Switch from C headers to C++ headers.
change const to constexpr
remove unnessary status judge
Remove leveldb::port::kLittleEndian.
Remove Windows workarounds in some tests.
Add Env::Remove{File,Dir} which obsolete Env::Delete{File,Dir}.
Defend against inclusion of windows.h in tests that invoke Env::DeleteFile.
Add WITHOUT ROWID to SQLite benchmark.
Switch testing harness to googletest.
Move CI to Visual Studio 2019.
Allow different C/C++ standards when this is used as a subproject.
Align CMake configuration with related projects.
Remove redundant PROJECT_SOURCE_DIR usage from CMake config.
Fix installed target definition.
Added return in Version::Get::State::Match to quiet warning.
Using CMake's check_cxx_compiler_flag to check support for -Wthread-safety.
Fix tsan problem in env_test.
Simplify unlocking in DeleteObsoleteFiles.
Add "leveldb" subdirectory to public include paths.
Align EnvPosix and EnvWindows.
Disable exceptions and RTTI in CMake configuration.
cache Saver in State object
fix bug(uninitialized options pointer in State)
remove TODO in Version::ForEachOverlapping
use ForEachOverlapping to impl Get
unsigned char -> uint8_t
Add explicit typecasts to avoid compiler warning.
Guard DBImpl::versions_ by mutex_.
Converted two for-loops to while-loops.
Switch to using C++ 11 override specifier.
Added unit test for InternalKey::DecodeFrom with empty string.
Using std::ostringstream in key DebugString.
Fix EnvPosix tests on Travis CI.
Clean up util/coding.{h,cc}.
Initialize Stats::start_ before first use in Stats::Start().
Add argument definition for void c functions.
Consolidate benchmark code to benchmarks/.
Convert missed virtual -> override in db_test.cc.
don't check current key in DBIter::Next()
Add O_CLOEXEC to open calls.
broken db: fix assertion in leveldb::InternalKey::Encode, mark base as corrupt
set const property
reduce lock's range in DeleteObsoleteFiles
block_builder header file dependency fixed