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.
Add a benchmark "seekordered" to db_bench that reuses iterators across
increasing seeks. Add support to the benchmark to count comparisons made and to support common key prefix length. Change benchmark random seeds to be reproducible for entire benchmark suite executions but unique for threads in different benchmarks runs. This changes a benchmark suite of readrandom,seekrandom from having a 100% found ratio as previously it had the same seed used for fillrandom.
./db_bench --benchmarks=fillrandom,compact,seekordered --block_size=262144 --comparisons=1 --key_prefix=100
without this change (though with benchmark changes):
seekrandom : 55.309 micros/op; (631820 of 1000000 found)
Comparisons: 27001049
seekordered : 1.732 micros/op; (631882 of 1000000 found)
Comparisons: 26998402
with this change:
seekrandom : 55.866 micros/op; (631820 of 1000000 found)
Comparisons: 26952143
seekordered : 1.686 micros/op; (631882 of 1000000 found)
Comparisons: 25549369
For ordered seeking, this is a reduction of 5% comparisons and a 3% speedup. For random seeking (with single use iterators) the comparisons and speed are less than 1% and likely noise.
PiperOrigin-RevId: 351149832
Clang 10 includes the optimizations described in
https://bugs.llvm.org/show_bug.cgi?id=41761. This means that the
platform-independent implementations of {Decode,Encode}Fixed{32,64}()
compile to one instruction on the most recent Clang and GCC.
PiperOrigin-RevId: 306330166
leveldb::Env::DeleteFile was replaced with leveldb::Env::RemoveFile in
all tests. This allows us to remove workarounds for windows.h #defining
DeleteFile.
PiperOrigin-RevId: 289121105
The "DeleteFile" method name causes pain for Windows developers, because
<windows.h> #defines a DeleteFile macro to DeleteFileW or DeleteFileA.
Current code uses workarounds, like #undefining DeleteFile everywhere an
Env is declared, implemented, or used.
This CL removes the need for workarounds by renaming Env::DeleteFile to
Env::RemoveFile. For consistency, Env::DeleteDir is also renamed to
Env::RemoveDir. A few internal methods are also renamed for consistency.
Software that supports Windows is expected to migrate any Env
implementations and usage to Remove{File,Dir}, and never use the name
Env::Delete{File,Dir} in its code.
The renaming is done in a backwards-compatible way, at the risk of
making it slightly more difficult to build a new correct Env
implementation. The backwards compatibility is achieved using the
following hacks:
1) Env::Remove{File,Dir} methods are added, with a default
implementation that calls into Env::Delete{File,Dir}. This makes old
Env implementations compatible with code that calls into the updated
API.
2) The Env::Delete{File,Dir} methods are no longer pure virtuals.
Instead, they gain a default implementation that calls into
Env::Remove{File,Dir}. This makes updated Env implementations
compatible with code that calls into the old API.
The cost of this approach is that it's possible to write an Env without
overriding either Rename{File,Dir} or Delete{File,Dir}, without getting
a compiler warning. However, attempting to run the test suite will
immediately fail with an infinite call stack ending in
{Remove,Delete}{File,Dir}, making developers aware of the problem.
PiperOrigin-RevId: 288710907
