Summary:
folly DistributedMutex is faster than standard mutexes though
imposes some static obligations on usage. See
https://github.com/facebook/folly/blob/main/folly/synchronization/DistributedMutex.h
for details. Here we use this alternative for our Cache implementations
(especially LRUCache) for better locking performance, when RocksDB is
compiled with folly.
Also added information about which distributed mutex implementation is
being used to cache_bench output and to DB LOG.
Intended follow-up:
* Use DMutex in more places, perhaps improving API to support non-scoped
locking
* Fix linking with fbcode compiler (needs ROCKSDB_NO_FBCODE=1 currently)
Credit: Thanks Siying for reminding me about this line of work that was previously
left unfinished.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10179
Test Plan:
for correctness, existing tests. CircleCI config updated.
Also Meta-internal buck build updated.
For performance, ran simultaneous before & after cache_bench. Out of three
comparison runs, the middle improvement to ops/sec was +21%:
Baseline: USE_CLANG=1 DEBUG_LEVEL=0 make -j24 cache_bench (fbcode
compiler)
```
Complete in 20.201 s; Rough parallel ops/sec = 1584062
Thread ops/sec = 107176
Operation latency (ns):
Count: 32000000 Average: 9257.9421 StdDev: 122412.04
Min: 134 Median: 3623.0493 Max: 56918500
Percentiles: P50: 3623.05 P75: 10288.02 P99: 30219.35 P99.9: 683522.04 P99.99: 7302791.63
```
New: (add USE_FOLLY=1)
```
Complete in 16.674 s; Rough parallel ops/sec = 1919135 (+21%)
Thread ops/sec = 135487
Operation latency (ns):
Count: 32000000 Average: 7304.9294 StdDev: 108530.28
Min: 132 Median: 3777.6012 Max: 91030902
Percentiles: P50: 3777.60 P75: 10169.89 P99: 24504.51 P99.9: 59721.59 P99.99: 1861151.83
```
Reviewed By: anand1976
Differential Revision: D37182983
Pulled By: pdillinger
fbshipit-source-id: a17eb05f25b832b6a2c1356f5c657e831a5af8d1
Summary:
We make the size of the per-shard hash table fixed. The base level of the hash table is now preallocated with the required capacity. The user must provide an estimate of the size of the values.
Notice that even though the base level becomes fixed, the chains are still dynamic. Overall, the shard capacity mechanisms haven't changed, so we don't need to test this.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10154
Test Plan: `make -j24 check`
Reviewed By: pdillinger
Differential Revision: D37124451
Pulled By: guidotag
fbshipit-source-id: cba6ac76052fe0ec60b8ff4211b3de7650e80d0c
Summary:
FastLRUCache now only supports 16B keys. The tests have changed to reflect this.
Because the unit tests were designed for caches that accept any string as keys, some tests are no longer compatible with FastLRUCache. We have disabled those for runs with FastLRUCache. (We could potentially change all tests to use 16B keys, but we don't because the cache public API does not require this.)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10137
Test Plan: make -j24 check
Reviewed By: gitbw95
Differential Revision: D37083934
Pulled By: guidotag
fbshipit-source-id: be1719cf5f8364a9a32bc4555bce1a0de3833b0d
Summary:
Update SecondaryCache::CreateFromString and enable it to create sec cache based on the uri for CompressedSecondaryCache.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10132
Test Plan: Add unit tests.
Reviewed By: anand1976
Differential Revision: D36996997
Pulled By: gitbw95
fbshipit-source-id: 882ad563cff6d38b306a53426ad7e47273f34edc
Summary:
As seen in https://github.com/facebook/rocksdb/issues/10137, simply churning the cache key hashes (e.g.
by changing the raw cache keys) could trigger failure in this test, due
to possibility of some cache shard exceeding its portion of capacity
and evicting entries. Updated the test to be less fragile by using
greater margins, and added a pre-check for evictions, which doesn't
manifest as a race condition, before the main check that can race.
Also added stack trace handler to cache_test for debugging.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10145
Test Plan:
test thousands of iterations with gtest-parallel, including
with changes in https://github.com/facebook/rocksdb/issues/10137 that were surfacing the problem. Pre-check
without the fix would always fail with https://github.com/facebook/rocksdb/issues/10137
Reviewed By: guidotag
Differential Revision: D37058771
Pulled By: pdillinger
fbshipit-source-id: a7cf137967aef49c07ae9602d8523c63e7388fab
Summary:
cache_bench can now run with FastLRUCache.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10095
Test Plan:
- Temporarily add an ``assert(false)`` in the execution path that sets up the FastLRUCache. Run ``make -j24 cache_bench``. Then test the appropriate code is used by running ``./cache_bench -cache_type=fast_lru_cache`` and checking that the assert is called. Repeat for LRUCache.
- Verify that FastLRUCache (currently a clone of LRUCache) has similar latency distribution than LRUCache, by comparing the outputs of ``./cache_bench -cache_type=fast_lru_cache`` and ``./cache_bench -cache_type=lru_cache``.
Reviewed By: pdillinger
Differential Revision: D36875834
Pulled By: guidotag
fbshipit-source-id: eb2ad0bb32c2717a258a6ac66ed736e06f826cd8
Summary:
In LRU Cache mutex, we sometimes call malloc_usable_size() to calculate memory used by the metadata object. We prevent it by saving the charge + metadata size, rather than charge, inside the metadata itself. Within the mutex, usually only total charge is needed so we don't need to repeat.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10026
Test Plan: Run existing tests.
Reviewed By: pdillinger
Differential Revision: D36556253
fbshipit-source-id: f60c96d13cde3af77732e5548e4eac4182fa9801
Summary:
ToString() is created as some platform doesn't support std::to_string(). However, we've already used std::to_string() by mistake for 16 months (in db/db_info_dumper.cc). This commit just remove ToString().
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9955
Test Plan: Watch CI tests
Reviewed By: riversand963
Differential Revision: D36176799
fbshipit-source-id: bdb6dcd0e3a3ab96a1ac810f5d0188f684064471
Summary:
To support a project to prototype and evaluate algorithmic
enhancments and alternatives to LRUCache, here I have separated out
LRUCache into internal-only "FastLRUCache" and cut it down to
essentials, so that details like secondary cache handling and
priorities do not interfere with prototyping. These can be
re-integrated later as needed, along with refactoring to minimize code
duplication (which would slow down prototyping for now).
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9917
Test Plan:
unit tests updated to ensure basic functionality has (likely)
been preserved
Reviewed By: anand1976
Differential Revision: D35995554
Pulled By: pdillinger
fbshipit-source-id: d67b20b7ada3b5d3bfe56d897a73885894a1d9db
Summary:
This gives users the ability to examine the map populated by `GetMapProperty()` with property `kBlockCacheEntryStats`. It also sets us up for a possible future where cache reservations are configured according to `CacheEntryRole`s rather than flags coupled to roles.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9838
Test Plan:
- migrated test DBBlockCacheTest.CacheEntryRoleStats to use this API. That test verifies some of the contents are as expected
- added a DBPropertiesTest to verify the public map keys are present, and nothing else
Reviewed By: hx235
Differential Revision: D35629493
Pulled By: ajkr
fbshipit-source-id: 5c4356b8560e85d1f881fd32c44c15960b02fc68
Summary:
Especially after updating to C++17, I don't see a compelling case for
*requiring* any folly components in RocksDB. I was able to purge the existing
hard dependencies, and it can be quite difficult to strip out non-trivial components
from folly for use in RocksDB. (The prospect of doing that on F14 has changed
my mind on the best approach here.)
But this change creates an optional integration where we can plug in
components from folly at compile time, starting here with F14FastMap to replace
std::unordered_map when possible (probably no public APIs for example). I have
replaced the biggest CPU users of std::unordered_map with compile-time
pluggable UnorderedMap which will use F14FastMap when USE_FOLLY is set.
USE_FOLLY is always set in the Meta-internal buck build, and a simulation of
that is in the Makefile for public CI testing. A full folly build is not needed, but
checking out the full folly repo is much simpler for getting the dependency,
and anything else we might want to optionally integrate in the future.
Some picky details:
* I don't think the distributed mutex stuff is actually used, so it was easy to remove.
* I implemented an alternative to `folly::constexpr_log2` (which is much easier
in C++17 than C++11) so that I could pull out the hard dependencies on
`ConstexprMath.h`
* I had to add noexcept move constructors/operators to some types to make
F14's complainUnlessNothrowMoveAndDestroy check happy, and I added a
macro to make that easier in some common cases.
* Updated Meta-internal buck build to use folly F14Map (always)
No updates to HISTORY.md nor INSTALL.md as this is not (yet?) considered a
production integration for open source users.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9546
Test Plan:
CircleCI tests updated so that a couple of them use folly.
Most internal unit & stress/crash tests updated to use Meta-internal latest folly.
(Note: they should probably use buck but they currently use Makefile.)
Example performance improvement: when filter partitions are pinned in cache,
they are tracked by PartitionedFilterBlockReader::filter_map_ and we can build
a test that exercises that heavily. Build DB with
```
TEST_TMPDIR=/dev/shm/rocksdb ./db_bench -benchmarks=fillrandom -num=10000000 -disable_wal=1 -write_buffer_size=30000000 -bloom_bits=16 -compaction_style=2 -fifo_compaction_max_table_files_size_mb=10000 -fifo_compaction_allow_compaction=0 -partition_index_and_filters
```
and test with (simultaneous runs with & without folly, ~20 times each to see
convergence)
```
TEST_TMPDIR=/dev/shm/rocksdb ./db_bench_folly -readonly -use_existing_db -benchmarks=readrandom -num=10000000 -bloom_bits=16 -compaction_style=2 -fifo_compaction_max_table_files_size_mb=10000 -fifo_compaction_allow_compaction=0 -partition_index_and_filters -duration=40 -pin_l0_filter_and_index_blocks_in_cache
```
Average ops/s no folly: 26229.2
Average ops/s with folly: 26853.3 (+2.4%)
Reviewed By: ajkr
Differential Revision: D34181736
Pulled By: pdillinger
fbshipit-source-id: ffa6ad5104c2880321d8a1aa7187e00ab0d02e94
Summary:
The param name force_erase may be misleading, since the handle is erased only if it has last reference even if the param is set true.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9728
Reviewed By: pdillinger
Differential Revision: D35038673
Pulled By: gitbw95
fbshipit-source-id: 0d16d1e8fed17b97eba7fb53207119332f659a5f
Summary:
**Summary:**
RocksDB uses a block cache to reduce IO and make queries more efficient. The block cache is based on the LRU algorithm (LRUCache) and keeps objects containing uncompressed data, such as Block, ParsedFullFilterBlock etc. It allows the user to configure a second level cache (rocksdb::SecondaryCache) to extend the primary block cache by holding items evicted from it. Some of the major RocksDB users, like MyRocks, use direct IO and would like to use a primary block cache for uncompressed data and a secondary cache for compressed data. The latter allows us to mitigate the loss of the Linux page cache due to direct IO.
This PR includes a concrete implementation of rocksdb::SecondaryCache that integrates with compression libraries such as LZ4 and implements an LRU cache to hold compressed blocks.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9518
Test Plan:
In this PR, the lru_secondary_cache_test.cc includes the following tests:
1. The unit tests for the secondary cache with either compression or no compression, such as basic tests, fails tests.
2. The integration tests with both primary cache and this secondary cache .
**Follow Up:**
1. Statistics (e.g. compression ratio) will be added in another PR.
2. Once this implementation is ready, I will do some shadow testing and benchmarking with UDB to measure the impact.
Reviewed By: anand1976
Differential Revision: D34430930
Pulled By: gitbw95
fbshipit-source-id: 218d78b672a2f914856d8a90ff32f2f5b5043ded
Summary:
Drop support for some old compilers by requiring C++17 standard
(or higher). See https://github.com/facebook/rocksdb/issues/9388
First modification based on this is to remove some conditional compilation in slice.h (also
better for ODR)
Also in this PR:
* Fix some Makefile formatting that seems to affect ASSERT_STATUS_CHECKED config in
some cases
* Add c_test to NON_PARALLEL_TEST in Makefile
* Fix a clang-analyze reported "potential leak" in lru_cache_test
* Better "compatibility" definition of DEFINE_uint32 for old versions of gflags
* Fix a linking problem with shared libraries in Makefile (`./random_test: error while loading shared libraries: librocksdb.so.6.29: cannot open shared object file: No such file or directory`)
* Always set ROCKSDB_SUPPORT_THREAD_LOCAL and use thread_local (from C++11)
* TODO in later PR: clean up that obsolete flag
* Fix a cosmetic typo in c.h (https://github.com/facebook/rocksdb/issues/9488)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9481
Test Plan:
CircleCI config substantially updated.
* Upgrade to latest Ubuntu images for each release
* Generally prefer Ubuntu 20, but keep a couple Ubuntu 16 builds with oldest supported
compilers, to ensure compatibility
* Remove .circleci/cat_ignore_eagain except for Ubuntu 16 builds, because this is to work
around a kernel bug that should not affect anything but Ubuntu 16.
* Remove designated gcc-9 build, because the default linux build now uses GCC 9 from
Ubuntu 20.
* Add some `apt-key add` to fix some apt "couldn't be verified" errors
* Generally drop SKIP_LINK=1; work-around no longer needed
* Generally `add-apt-repository` before `apt-get update` as manual testing indicated the
reverse might not work.
Travis:
* Use gcc-7 by default (remove specific gcc-7 and gcc-4.8 builds)
* TODO in later PR: fix s390x "Assembler messages: Error: invalid switch -march=z14" failure
AppVeyor:
* Completely dropped because we are dropping VS2015 support and CircleCI covers
VS >= 2017
Also local testing with old gflags (out of necessity when using ROCKSDB_NO_FBCODE=1).
Reviewed By: mrambacher
Differential Revision: D33946377
Pulled By: pdillinger
fbshipit-source-id: ae077c823905b45370a26c0103ada119459da6c1
Summary:
Follow-up to https://github.com/facebook/rocksdb/issues/9126
Added new unit tests to validate some of the claims of guaranteed uniqueness
within certain large bounds.
Also cleaned up the cache_bench -stress-cache-key tool with better comments
and description.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9329
Test Plan: no changes to production code
Reviewed By: mrambacher
Differential Revision: D33269328
Pulled By: pdillinger
fbshipit-source-id: 3a2b684a6b2b15f79dc872e563e3d16563be26de
Summary:
This change standardizes on a new 16-byte cache key format for
block cache (incl compressed and secondary) and persistent cache (but
not table cache and row cache).
The goal is a really fast cache key with practically ideal stability and
uniqueness properties without external dependencies (e.g. from FileSystem).
A fixed key size of 16 bytes should enable future optimizations to the
concurrent hash table for block cache, which is a heavy CPU user /
bottleneck, but there appears to be measurable performance improvement
even with no changes to LRUCache.
This change replaces a lot of disjointed and ugly code handling cache
keys with calls to a simple, clean new internal API (cache_key.h).
(Preserving the old cache key logic under an option would be very ugly
and likely negate the performance gain of the new approach. Complete
replacement carries some inherent risk, but I think that's acceptable
with sufficient analysis and testing.)
The scheme for encoding new cache keys is complicated but explained
in cache_key.cc.
Also: EndianSwapValue is moved to math.h to be next to other bit
operations. (Explains some new include "math.h".) ReverseBits operation
added and unit tests added to hash_test for both.
Fixes https://github.com/facebook/rocksdb/issues/7405 (presuming a root cause)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9126
Test Plan:
### Basic correctness
Several tests needed updates to work with the new functionality, mostly
because we are no longer relying on filesystem for stable cache keys
so table builders & readers need more context info to agree on cache
keys. This functionality is so core, a huge number of existing tests
exercise the cache key functionality.
### Performance
Create db with
`TEST_TMPDIR=/dev/shm ./db_bench -bloom_bits=10 -benchmarks=fillrandom -num=3000000 -partition_index_and_filters`
And test performance with
`TEST_TMPDIR=/dev/shm ./db_bench -readonly -use_existing_db -bloom_bits=10 -benchmarks=readrandom -num=3000000 -duration=30 -cache_index_and_filter_blocks -cache_size=250000 -threads=4`
using DEBUG_LEVEL=0 and simultaneous before & after runs.
Before ops/sec, avg over 100 runs: 121924
After ops/sec, avg over 100 runs: 125385 (+2.8%)
### Collision probability
I have built a tool, ./cache_bench -stress_cache_key to broadly simulate host-wide cache activity
over many months, by making some pessimistic simplifying assumptions:
* Every generated file has a cache entry for every byte offset in the file (contiguous range of cache keys)
* All of every file is cached for its entire lifetime
We use a simple table with skewed address assignment and replacement on address collision
to simulate files coming & going, with quite a variance (super-Poisson) in ages. Some output
with `./cache_bench -stress_cache_key -sck_keep_bits=40`:
```
Total cache or DBs size: 32TiB Writing 925.926 MiB/s or 76.2939TiB/day
Multiply by 9.22337e+18 to correct for simulation losses (but still assume whole file cached)
```
These come from default settings of 2.5M files per day of 32 MB each, and
`-sck_keep_bits=40` means that to represent a single file, we are only keeping 40 bits of
the 128-bit cache key. With file size of 2\*\*25 contiguous keys (pessimistic), our simulation
is about 2\*\*(128-40-25) or about 9 billion billion times more prone to collision than reality.
More default assumptions, relatively pessimistic:
* 100 DBs in same process (doesn't matter much)
* Re-open DB in same process (new session ID related to old session ID) on average
every 100 files generated
* Restart process (all new session IDs unrelated to old) 24 times per day
After enough data, we get a result at the end:
```
(keep 40 bits) 17 collisions after 2 x 90 days, est 10.5882 days between (9.76592e+19 corrected)
```
If we believe the (pessimistic) simulation and the mathematical generalization, we would need to run a billion machines all for 97 billion days to expect a cache key collision. To help verify that our generalization ("corrected") is robust, we can make our simulation more precise with `-sck_keep_bits=41` and `42`, which takes more running time to get enough data:
```
(keep 41 bits) 16 collisions after 4 x 90 days, est 22.5 days between (1.03763e+20 corrected)
(keep 42 bits) 19 collisions after 10 x 90 days, est 47.3684 days between (1.09224e+20 corrected)
```
The generalized prediction still holds. With the `-sck_randomize` option, we can see that we are beating "random" cache keys (except offsets still non-randomized) by a modest amount (roughly 20x less collision prone than random), which should make us reasonably comfortable even in "degenerate" cases:
```
197 collisions after 1 x 90 days, est 0.456853 days between (4.21372e+18 corrected)
```
I've run other tests to validate other conditions behave as expected, never behaving "worse than random" unless we start chopping off structured data.
Reviewed By: zhichao-cao
Differential Revision: D33171746
Pulled By: pdillinger
fbshipit-source-id: f16a57e369ed37be5e7e33525ace848d0537c88f
Summary:
Added missing include, and cleaned up to make same mistake less
likely in future (minimize conditional compilation)
Fixes https://github.com/facebook/rocksdb/issues/9183
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9209
Test Plan: added to existing test
Reviewed By: mrambacher
Differential Revision: D32631390
Pulled By: pdillinger
fbshipit-source-id: 63a0501855cf5fac9e22ca1e5c4f53725dbf3f93
Summary:
Note: This PR is the 4th part of a bigger PR stack (https://github.com/facebook/rocksdb/pull/9073) and will rebase/merge only after the first three PRs (https://github.com/facebook/rocksdb/pull/9070, https://github.com/facebook/rocksdb/pull/9071, https://github.com/facebook/rocksdb/pull/9130) merge.
**Context:**
Similar to https://github.com/facebook/rocksdb/pull/8428, this PR is to track memory usage during (new) Bloom Filter (i.e,FastLocalBloom) and Ribbon Filter (i.e, Ribbon128) construction, moving toward the goal of [single global memory limit using block cache capacity](https://github.com/facebook/rocksdb/wiki/Projects-Being-Developed#improving-memory-efficiency). It also constrains the size of the banding portion of Ribbon Filter during construction by falling back to Bloom Filter if that banding is, at some point, larger than the available space in the cache under `LRUCacheOptions::strict_capacity_limit=true`.
The option to turn on this feature is `BlockBasedTableOptions::reserve_table_builder_memory = true` which by default is set to `false`. We [decided](https://github.com/facebook/rocksdb/pull/9073#discussion_r741548409) not to have separate option for separate memory user in table building therefore their memory accounting are all bundled under one general option.
**Summary:**
- Reserved/released cache for creation/destruction of three main memory users with the passed-in `FilterBuildingContext::cache_res_mgr` during filter construction:
- hash entries (i.e`hash_entries`.size(), we bucket-charge hash entries during insertion for performance),
- banding (Ribbon Filter only, `bytes_coeff_rows` +`bytes_result_rows` + `bytes_backtrack`),
- final filter (i.e, `mutable_buf`'s size).
- Implementation details: in order to use `CacheReservationManager::CacheReservationHandle` to account final filter's memory, we have to store the `CacheReservationManager` object and `CacheReservationHandle` for final filter in `XXPH3BitsFilterBuilder` as well as explicitly delete the filter bits builder when done with the final filter in block based table.
- Added option fo run `filter_bench` with this memory reservation feature
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9073
Test Plan:
- Added new tests in `db_bloom_filter_test` to verify filter construction peak cache reservation under combination of `BlockBasedTable::Rep::FilterType` (e.g, `kFullFilter`, `kPartitionedFilter`), `BloomFilterPolicy::Mode`(e.g, `kFastLocalBloom`, `kStandard128Ribbon`, `kDeprecatedBlock`) and `BlockBasedTableOptions::reserve_table_builder_memory`
- To address the concern for slow test: tests with memory reservation under `kFullFilter` + `kStandard128Ribbon` and `kPartitionedFilter` take around **3000 - 6000 ms** and others take around **1500 - 2000 ms**, in total adding **20000 - 25000 ms** to the test suit running locally
- Added new test in `bloom_test` to verify Ribbon Filter fallback on large banding in FullFilter
- Added test in `filter_bench` to verify that this feature does not significantly slow down Bloom/Ribbon Filter construction speed. Local result averaged over **20** run as below:
- FastLocalBloom
- baseline `./filter_bench -impl=2 -quick -runs 20 | grep 'Build avg'`:
- **Build avg ns/key: 29.56295** (DEBUG_LEVEL=1), **29.98153** (DEBUG_LEVEL=0)
- new feature (expected to be similar as above)`./filter_bench -impl=2 -quick -runs 20 -reserve_table_builder_memory=true | grep 'Build avg'`:
- **Build avg ns/key: 30.99046** (DEBUG_LEVEL=1), **30.48867** (DEBUG_LEVEL=0)
- new feature of RibbonFilter with fallback (expected to be similar as above) `./filter_bench -impl=2 -quick -runs 20 -reserve_table_builder_memory=true -strict_capacity_limit=true | grep 'Build avg'` :
- **Build avg ns/key: 31.146975** (DEBUG_LEVEL=1), **30.08165** (DEBUG_LEVEL=0)
- Ribbon128
- baseline `./filter_bench -impl=3 -quick -runs 20 | grep 'Build avg'`:
- **Build avg ns/key: 129.17585** (DEBUG_LEVEL=1), **130.5225** (DEBUG_LEVEL=0)
- new feature (expected to be similar as above) `./filter_bench -impl=3 -quick -runs 20 -reserve_table_builder_memory=true | grep 'Build avg' `:
- **Build avg ns/key: 131.61645** (DEBUG_LEVEL=1), **132.98075** (DEBUG_LEVEL=0)
- new feature of RibbonFilter with fallback (expected to be a lot faster than above due to fallback) `./filter_bench -impl=3 -quick -runs 20 -reserve_table_builder_memory=true -strict_capacity_limit=true | grep 'Build avg'` :
- **Build avg ns/key: 52.032965** (DEBUG_LEVEL=1), **52.597825** (DEBUG_LEVEL=0)
- And the warning message of `"Cache reservation for Ribbon filter banding failed due to cache full"` is indeed logged to console.
Reviewed By: pdillinger
Differential Revision: D31991348
Pulled By: hx235
fbshipit-source-id: 9336b2c60f44d530063da518ceaf56dac5f9df8e
Summary:
We have three layers of block cache that often use the same key
but map to different physical data:
* BlockBasedTableOptions::block_cache
* BlockBasedTableOptions::block_cache_compressed
* BlockBasedTableOptions::persistent_cache
If any two of these happen to share an underlying implementation and key
space (insertion into one shows up in another), then memory safety is
broken. The simplest case is block_cache == block_cache_compressed.
(Credit mrambacher for asking about this case in a review.)
With this change, we explicitly check for overlap and preemptively and
safely fail with a Status code.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9172
Test Plan: test added. Crashes without new check
Reviewed By: anand1976
Differential Revision: D32465659
Pulled By: pdillinger
fbshipit-source-id: 3876b45b6dce6167e5a7a642725ddc86b96f8e40
Summary:
Note: This PR is the 3rd PR of a bigger PR stack (https://github.com/facebook/rocksdb/issues/9073) and depends on the second PR (https://github.com/facebook/rocksdb/pull/9071). **See changes from this PR only 00447324d0**
Context:
pdillinger brought up a good [point](https://github.com/facebook/rocksdb/pull/9073#discussion_r741478309) about lacking RAII support for per cache reservation in `CacheReservationManager` when reviewing https://github.com/facebook/rocksdb/pull/9073.
To summarize the discussion, the current API `CacheReservationManager::UpdateCacheReservation()` requires callers to explicitly calculate and pass in a correct`new_mem_used` to release a cache reservation (if they don't want to rely on the clean-up during `CacheReservationManager`'s destruction - such as they want to release it earlier).
While this implementation has convenience in some use-case such as `WriteBufferManager`, where [reservation](https://github.com/facebook/rocksdb/blob/main/memtable/write_buffer_manager.cc#L69-L91) and [release](https://github.com/facebook/rocksdb/blob/main/memtable/write_buffer_manager.cc#L109-L129) amounts do not necessarily correspond symmetrically and thus a flexible `new_mem_used` inputing is needed, it can be prone to caller's calculation error as well as cause a mass of codes in releasing cache in other use-case such as filter construction, where reservation and release amounts do correspond symmetrically and many code paths requiring a cache release, as [pointed](https://github.com/facebook/rocksdb/pull/9073#discussion_r741478309) out by pdillinger.
Therefore we decided to provide a new API in `CacheReservationManager` to update reservation with better RAII support for per cache reservation, using a handle to manage the life time of that particular cache reservation.
- Added a new class `CacheReservationHandle`
- Added a new API `CacheReservationManager::MakeCacheReservation()` that outputs a `CacheReservationHandle` for managing the reservation
- Updated class comments to clarify two different cache reservation methods
Tests:
- Passing new tests
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9130
Reviewed By: pdillinger
Differential Revision: D32199446
Pulled By: hx235
fbshipit-source-id: 1cba7c636e5ecfb55b0c1e0c2d218cc9b5b30b4e
Summary:
Note: This PR is the 2nd PR of a bigger PR stack (https://github.com/facebook/rocksdb/pull/9073).
Context:
`CacheReservationManager::UpdateCacheReservation(std::size_t new_memory_used)` accepts an accumulated total memory used (e.g, used 10MB so far) instead of usage change (e.g, increase by 5 MB, decrease by 5 MB). It has benefits including consolidating API for increase and decrease as described in https://github.com/facebook/rocksdb/pull/8506.
However, not every `CacheReservationManager` user keeps track of this accumulated total memory usage. For example, Bloom/Ribbon Filter construction (e.g, [here](822d729fcd/table/block_based/filter_policy.cc (L587)) in https://github.com/facebook/rocksdb/pull/9073) does not while WriteBufferManager and compression dictionary buffering do.
Considering future users might or might not keep track of this counter and implementing this counter within `CacheReservationManager` is easy due to the passed-in `std::size_t new_memory_used` in calling `CacheReservationManager::UpdateCacheReservation(std::size_t new_memory_used)`, it is proposed to add a new API `CacheReservationManager::GetTotalMemoryUsage()`.
As noted in the API comments, since `CacheReservationManager` is NOT thread-safe, external synchronization is
needed in calling `UpdateCacheReservation()` if you want `GetTotalMemoryUsed()` returns the indeed latest memory used.
- Added and updated private counter `memory_used_` every time `CacheReservationManager::UpdateCacheReservation(std::size_t new_memory_used)` is called regardless if the call returns non-okay status
- Added `CacheReservationManager::GetTotalMemoryUsage()` to return `memory_used_`
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9071
Test Plan:
- Passing new tests
- Passing existing tests
Reviewed By: ajkr
Differential Revision: D31887813
Pulled By: hx235
fbshipit-source-id: 9a09f0c8683822673260362894c878b61ee60ceb
Summary:
Note: it might conflict with another CRM related PR https://github.com/facebook/rocksdb/pull/9071 and so will merge after that's merged.
Context:
As `CacheReservationManager` being used by more memory users, it is convenient to retrieve the dummy entry size for `CacheReservationManager` instead of hard-coding `256 * 1024` in writing tests. Plus it allows more flexibility to change our implementation on dummy entry size.
A follow-up PR is needed to replace those hard-coded dummy entry size value in `db_test2.cc`, `db_write_buffer_manager_test.cc`, `write_buffer_manager_test.cc`, `table_test.cc` and the ones introduced in https://github.com/facebook/rocksdb/pull/9072#issue-1034326069.
- Exposed the private static constexpr `kDummyEntrySize` through public static `CacheReservationManager::GetDummyEntrySize()`
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9072
Test Plan:
- Passing new tests
- Passing existing tests
Reviewed By: ajkr
Differential Revision: D32043684
Pulled By: hx235
fbshipit-source-id: ddefc6921c052adab6a2cda2394eb26da3076a50
Summary:
Currently, if Secondary Cache is provided to the lru cache, it is used by default. We add CacheTier to advanced_options.h to describe the cache tier we used. Add a `lowest_used_cache_tier` option to `DBOptions` (immutable) and pass it to BlockBasedTableReader to decide if secondary cache will be used or not. By default it is `CacheTier::kNonVolatileTier`, which means, we always use both block cache (kVolatileTier) and secondary cache (kNonVolatileTier). By set it to `CacheTier::kVolatileTier`, the DB will not use the secondary cache.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9050
Test Plan: added new tests
Reviewed By: anand1976
Differential Revision: D31744769
Pulled By: zhichao-cao
fbshipit-source-id: a0575ebd23e1c6dfcfc2b4c8578764e73b15bce6
Summary:
Background: Cache warming up will cause potential read performance degradation due to reading blocks from storage to the block cache. Since in production, the workload and access pattern to a certain DB is stable, it is a potential solution to dump out the blocks belonging to a certain DB to persist storage (e.g., to a file) and bulk-load the blocks to Secondary cache before the DB is relaunched. For example, when migrating a DB form host A to host B, it will take a short period of time, the access pattern to blocks in the block cache will not change much. It is efficient to dump out the blocks of certain DB, migrate to the destination host and insert them to the Secondary cache before we relaunch the DB.
Design: we introduce the interface of CacheDumpWriter and CacheDumpRead for user to store the blocks dumped out from block cache. RocksDB will encode all the information and send the string to the writer. User can implement their own writer it they want. CacheDumper and CacheLoad are introduced to save the blocks and load the blocks respectively.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8912
Test Plan: add new tests to lru_cache_test and pass make check.
Reviewed By: pdillinger
Differential Revision: D31452871
Pulled By: zhichao-cao
fbshipit-source-id: 11ab4f5d03e383f476947116361d54188d36ec48
Summary:
It's always annoying to find a header does not include its own
dependencies and only works when included after other includes. This
change adds `make check-headers` which validates that each header can
be included at the top of a file. Some headers are excluded e.g. because
of platform or external dependencies.
rocksdb_namespace.h had to be re-worked slightly to enable checking for
failure to include it. (ROCKSDB_NAMESPACE is a valid namespace name.)
Fixes mostly involve adding and cleaning up #includes, but for
FileTraceWriter, a constructor was out-of-lined to make a forward
declaration sufficient.
This check is not currently run with `make check` but is added to
CircleCI build-linux-unity since that one is already relatively fast.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8893
Test Plan: existing tests and resolving issues detected by new check
Reviewed By: mrambacher
Differential Revision: D30823300
Pulled By: pdillinger
fbshipit-source-id: 9fff223944994c83c105e2e6496d24845dc8e572
Summary:
Context/Summary: this PR is to clarify what the parameter new_memory_used is in CacheReservationManager::UpdateCacheReservation
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8895
Test Plan:
- Passing existing test
- Make format
Reviewed By: jay-zhuang
Differential Revision: D30844814
Pulled By: hx235
fbshipit-source-id: 3177f7abf5668ea9e73818ceaa355566f03acabc
Summary:
Context:
Some data blocks are temporarily buffered in memory in BlockBasedTableBuilder for building compression dictionary used in data block compression. Currently this memory usage is not counted toward our global memory usage utilizing block cache capacity. To improve that, this PR charges that memory usage into the block cache to achieve better memory tracking and limiting.
- Reserve memory in block cache for buffered data blocks that are used to build a compression dictionary
- Release all the memory associated with buffering the data blocks mentioned above in EnterUnbuffered(), which is called when (a) buffer limit is exceeded after buffering OR (b) the block cache becomes full after reservation OR (c) BlockBasedTableBuilder calls Finish()
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8428
Test Plan:
- Passing existing unit tests
- Passing new unit tests
Reviewed By: ajkr
Differential Revision: D30755305
Pulled By: hx235
fbshipit-source-id: 6e66665020b775154a94c4c5e0f2adaeaff13981
Summary:
* Don't hardcode namespace rocksdb (use ROCKSDB_NAMESPACE)
* Don't #include <rocksdb/...> (use double quotes)
* Support putting NOCOMMIT (any case) in source code that should not be
committed/pushed in current state.
These will be run with `make check` and in GitHub actions
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8821
Test Plan: existing tests, manually try out new checks
Reviewed By: zhichao-cao
Differential Revision: D30791726
Pulled By: pdillinger
fbshipit-source-id: 399c883f312be24d9e55c58951d4013e18429d92
Summary:
Old typedef syntax is confusing
Most but not all changes with
perl -pi -e 's/typedef (.*) ([a-zA-Z0-9_]+);/using $2 = $1;/g' list_of_files
make format
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8751
Test Plan: existing
Reviewed By: zhichao-cao
Differential Revision: D30745277
Pulled By: pdillinger
fbshipit-source-id: 6f65f0631c3563382d43347896020413cc2366d9
Summary:
In ```LRUCacheShard::Promote```, a reference is released outside the LRU mutex. Fix the race condition.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8717
Reviewed By: zhichao-cao
Differential Revision: D30649206
Pulled By: anand1976
fbshipit-source-id: 09c0af05b2294a7fe2c02876a61b0bad6e3ada61
Summary:
Context:
To help cap various memory usage by a single limit of the block cache capacity, we charge the memory usage through inserting/releasing dummy entries in the block cache. CacheReservationManager is such a class (non thread-safe) responsible for inserting/removing dummy entries to reserve cache space for memory used by the class user.
- Refactored the inner private class CacheRep of WriteBufferManager into public CacheReservationManager class for reusability such as for https://github.com/facebook/rocksdb/pull/8428
- Encapsulated implementation details of cache key generation and dummy entries insertion/release in cache reservation as discussed in https://github.com/facebook/rocksdb/pull/8506#discussion_r666550838
- Consolidated increase/decrease cache reservation into one API - UpdateCacheReservation.
- Adjusted the previous dummy entry release algorithm in decreasing cache reservation to be loop-releasing dummy entries to stay symmetric to dummy entry insertion algorithm
- Made the previous dummy entry release algorithm in delayed decrease mode more aggressive for better decreasing cache reservation when memory used is less likely to increase back.
Previously, the algorithms only release 1 dummy entries when new_mem_used < 3/4 * cache_allocated_size_ and cache_allocated_size_ - kSizeDummyEntry > new_mem_used.
Now, the algorithms loop-releases as many dummy entries as possible when new_mem_used < 3/4 * cache_allocated_size_.
- Updated WriteBufferManager's test cases to adapt to changes on the release algorithm mentioned above and left comment for some test cases for clarity
- Replaced the previous cache key prefix generation (utilizing object address related to the cache client) with one that utilizes Cache->NewID() to prevent cache-key collision among dummy entry clients sharing the same cache.
The specific collision we are preventing happens when the object address is reused for a new cache-key prefix while the old cache-key using that same object address in its prefix still exists in the cache. This could happen due to that, under LRU cache policy, there is a possible delay in releasing a cache entry after the cache client object owning that cache entry get deallocated. In this case, the object address related to the cache client object can get reused for other client object to generate a new cache-key prefix.
This prefix generation can be made obsolete after Peter's unification of all the code generating cache key, mentioned in https://github.com/facebook/rocksdb/pull/8506#discussion_r667265255
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8506
Test Plan:
- Passing the added unit tests cache_reservation_manager_test.cc
- Passing existing and adjusted write_buffer_manager_test.cc
Reviewed By: ajkr
Differential Revision: D29644135
Pulled By: hx235
fbshipit-source-id: 0fc93fbfe4a40bb41be85c314f8f2bafa8b741f7
Summary:
Add a stat for secondary cache hits. The ```Cache::Lookup``` API had an unused ```stats``` parameter. This PR uses that to pass the pointer to a ```Statistics``` object that ```LRUCache``` uses to record the stat.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8666
Test Plan: Update a unit test in lru_cache_test
Reviewed By: zhichao-cao
Differential Revision: D30353816
Pulled By: anand1976
fbshipit-source-id: 2046f78b460428877a26ffdd2bb914ae47dfbe77
Summary:
The PerThreadDBPath has already specified a slash. It does not need to be specified when initializing the test path.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8555
Reviewed By: ajkr
Differential Revision: D29758399
Pulled By: jay-zhuang
fbshipit-source-id: 6d2b878523e3e8580536e2829cb25489844d9011
Summary:
I previously didn't notice the DB mutex was being held during
block cache entry stat scans, probably because I primarily checked for
read performance regressions, because they require the block cache and
are traditionally latency-sensitive.
This change does some refactoring to avoid holding DB mutex and to
avoid triggering and waiting for a scan in GetProperty("rocksdb.cfstats").
Some tests have to be updated because now the stats collector is
populated in the Cache aggressively on DB startup rather than lazily.
(I hope to clean up some of this added complexity in the future.)
This change also ensures proper treatment of need_out_of_mutex for
non-int DB properties.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8538
Test Plan:
Added unit test logic that uses sync points to fail if the DB mutex
is held during a scan, covering the various ways that a scan might be
triggered.
Performance test - the known impact to holding the DB mutex is on
TransactionDB, and the easiest way to see the impact is to hack the
scan code to almost always miss and take an artificially long time
scanning. Here I've injected an unconditional 5s sleep at the call to
ApplyToAllEntries.
Before (hacked):
$ TEST_TMPDIR=/dev/shm ./db_bench.base_xxx -benchmarks=randomtransaction,stats -cache_index_and_filter_blocks=1 -bloom_bits=10 -partition_index_and_filters=1 -duration=30 -stats_dump_period_sec=12 -cache_size=100000000 -statistics -transaction_db 2>&1 | egrep 'db.db.write.micros|micros/op'
randomtransaction : 433.219 micros/op 2308 ops/sec; 0.1 MB/s ( transactions:78999 aborts:0)
rocksdb.db.write.micros P50 : 16.135883 P95 : 36.622503 P99 : 66.036115 P100 : 5000614.000000 COUNT : 149677 SUM : 8364856
$ TEST_TMPDIR=/dev/shm ./db_bench.base_xxx -benchmarks=randomtransaction,stats -cache_index_and_filter_blocks=1 -bloom_bits=10 -partition_index_and_filters=1 -duration=30 -stats_dump_period_sec=12 -cache_size=100000000 -statistics -transaction_db 2>&1 | egrep 'db.db.write.micros|micros/op'
randomtransaction : 448.802 micros/op 2228 ops/sec; 0.1 MB/s ( transactions:75999 aborts:0)
rocksdb.db.write.micros P50 : 16.629221 P95 : 37.320607 P99 : 72.144341 P100 : 5000871.000000 COUNT : 143995 SUM : 13472323
Notice the 5s P100 write time.
After (hacked):
$ TEST_TMPDIR=/dev/shm ./db_bench.new_xxx -benchmarks=randomtransaction,stats -cache_index_and_filter_blocks=1 -bloom_bits=10 -partition_index_and_filters=1 -duration=30 -stats_dump_period_sec=12 -cache_size=100000000 -statistics -transaction_db 2>&1 | egrep 'db.db.write.micros|micros/op'
randomtransaction : 303.645 micros/op 3293 ops/sec; 0.1 MB/s ( transactions:98999 aborts:0)
rocksdb.db.write.micros P50 : 16.061871 P95 : 33.978834 P99 : 60.018017 P100 : 616315.000000 COUNT : 187619 SUM : 4097407
$ TEST_TMPDIR=/dev/shm ./db_bench.new_xxx -benchmarks=randomtransaction,stats -cache_index_and_filter_blocks=1 -bloom_bits=10 -partition_index_and_filters=1 -duration=30 -stats_dump_period_sec=12 -cache_size=100000000 -statistics -transaction_db 2>&1 | egrep 'db.db.write.micros|micros/op'
randomtransaction : 310.383 micros/op 3221 ops/sec; 0.1 MB/s ( transactions:96999 aborts:0)
rocksdb.db.write.micros P50 : 16.270026 P95 : 35.786844 P99 : 64.302878 P100 : 603088.000000 COUNT : 183819 SUM : 4095918
P100 write is now ~0.6s. Not good, but it's the same even if I completely bypass all the scanning code:
$ TEST_TMPDIR=/dev/shm ./db_bench.new_skip -benchmarks=randomtransaction,stats -cache_index_and_filter_blocks=1 -bloom_bits=10 -partition_index_and_filters=1 -duration=30 -stats_dump_period_sec=12 -cache_size=100000000 -statistics -transaction_db 2>&1 | egrep 'db.db.write.micros|micros/op'
randomtransaction : 311.365 micros/op 3211 ops/sec; 0.1 MB/s ( transactions:96999 aborts:0)
rocksdb.db.write.micros P50 : 16.274362 P95 : 36.221184 P99 : 68.809783 P100 : 649808.000000 COUNT : 183819 SUM : 4156767
$ TEST_TMPDIR=/dev/shm ./db_bench.new_skip -benchmarks=randomtransaction,stats -cache_index_and_filter_blocks=1 -bloom_bits=10 -partition_index_and_filters=1 -duration=30 -stats_dump_period_sec=12 -cache_size=100000000 -statistics -transaction_db 2>&1 | egrep 'db.db.write.micros|micros/op'
randomtransaction : 308.395 micros/op 3242 ops/sec; 0.1 MB/s ( transactions:97999 aborts:0)
rocksdb.db.write.micros P50 : 16.106222 P95 : 37.202403 P99 : 67.081875 P100 : 598091.000000 COUNT : 185714 SUM : 4098832
No substantial difference.
Reviewed By: siying
Differential Revision: D29738847
Pulled By: pdillinger
fbshipit-source-id: 1c5c155f5a1b62e4fea0fd4eeb515a8b7474027b
Summary:
Some bits are mutated and read while holding a lock, other
immutable bits (esp. secondary cache compatibility) can be read by
arbitrary threads without holding a lock. AFAIK, this doesn't cause an
issue on any architecture we care about, because you will get some
legitimate version of the value that includes the initialization, as
long as synchronization guarantees the initialization happens before the
read.
I've only seen this in https://github.com/facebook/rocksdb/issues/8538 so far, but it should be fixed regardless.
Otherwise, we'll surely get these false reports again some time.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8539
Test Plan: some local TSAN test runs and in CircleCI
Reviewed By: zhichao-cao
Differential Revision: D29720262
Pulled By: pdillinger
fbshipit-source-id: 365fd7e565577c648815161f71b339bcb5ce12d5
Summary:
When the secondary cache lookup fails, we may still allocate a handle and charge the cache for metadata usage. If the cache is full, this can cause the usage to go over capacity. Later, when a (unrelated) handle is released, it trips up an assertion that checks that usage is less than capacity. To prevent this assertion failure, don't charge the cache for a failed secondary cache lookup.
Tests:
Run crash_test
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8470
Reviewed By: zhichao-cao
Differential Revision: D29474713
Pulled By: anand1976
fbshipit-source-id: 27191969c95470a7b070d292b458efce71395bf2
Summary:
Tsan complains due to a perceived race condition in accessing LRUHandle flags. One thread calls ```LRUHandle::SetHit()``` from ```LRUCacheShard::Lookup()```, while another thread calls ```LRUHandle::IsPending()``` from ```LRUCacheShard::IsReady()```. The latter call is from ```MultiGet```. It doesn't actually have to call ```IsReady``` since a null value indicates the cache handle is not ready, so its sufficient to check for a null value.
Also modify ```IsReady``` to acquire the LRU shard mutex.
Tests:
1. make check
2. Run tsan_crash
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8433
Reviewed By: zhichao-cao
Differential Revision: D29278030
Pulled By: anand1976
fbshipit-source-id: 0c9fed56d12eda853e72dadebe75038361bd257f
Summary:
Implement the ```WaitAll()``` interface in ```LRUCache``` to allow callers to issue multiple lookups in parallel and wait for all of them to complete. Modify ```MultiGet``` to use this to parallelize the secondary cache lookups in order to reduce the overall latency. A call to ```cache->Lookup()``` returns a handle that has an incomplete value (nullptr), and the caller can call ```cache->IsReady()``` to check whether the lookup is complete, and pass a vector of handles to ```WaitAll``` to wait for completion. If any of the lookups fail, ```MultiGet``` will read the block from the SST file.
Another change in this PR is to rename ```SecondaryCacheHandle``` to ```SecondaryCacheResultHandle``` as it more accurately describes the return result of the secondary cache lookup, which is more like a future.
Tests:
1. Add unit tests in lru_cache_test
2. Benchmark results with no secondary cache configured
Master -
```
readrandom : 41.175 micros/op 388562 ops/sec; 106.7 MB/s (7277999 of 7277999 found)
readrandom : 41.217 micros/op 388160 ops/sec; 106.6 MB/s (7274999 of 7274999 found)
multireadrandom : 10.309 micros/op 1552082 ops/sec; (28908992 of 28908992 found)
multireadrandom : 10.321 micros/op 1550218 ops/sec; (29081984 of 29081984 found)
```
This PR -
```
readrandom : 41.158 micros/op 388723 ops/sec; 106.8 MB/s (7290999 of 7290999 found)
readrandom : 41.185 micros/op 388463 ops/sec; 106.7 MB/s (7287999 of 7287999 found)
multireadrandom : 10.277 micros/op 1556801 ops/sec; (29346944 of 29346944 found)
multireadrandom : 10.253 micros/op 1560539 ops/sec; (29274944 of 29274944 found)
```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8405
Reviewed By: zhichao-cao
Differential Revision: D29190509
Pulled By: anand1976
fbshipit-source-id: 6f8eff6246712af8a297cfe22ea0d1c3b2a01bb0
Summary:
Longstanding tech debt
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8379
Test Plan: Better than not having an API contract
Reviewed By: jay-zhuang
Differential Revision: D29011131
Pulled By: pdillinger
fbshipit-source-id: 2c4796177733651954024fc17875f8642ca08d09
Peter Dillinger