Summary:
For write unprepared, some applications may bypass the transaction api, and write keys directly into the write batch. However, since they are not tracked, rollbacks (both for savepoint and transaction) are not aware that these keys have to be rolled back.
The fix is to track them in `WriteUnpreparedTxn::untracked_keys_`. This is populated whenever we flush unprepared batches into the DB.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6404
Differential Revision: D19842023
Pulled By: lth
fbshipit-source-id: a9edfc643d5c905fc89da9a9a9094d30c9b70108
Summary:
`index` can be replaced by `iter`, saving the computation of `index++`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6406
Test Plan: make check
Differential Revision: D19905056
Pulled By: cheng-chang
fbshipit-source-id: add4638959c0d2e4e77a11f3fa04ffabaf0de790
Summary:
Previously, when recovering version set, LoadTableHandlers failures are ignored.
If paranoid_checks is true, this failure should not be ignored, otherwise, the opened db might be in an inconsistent state.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6368
Test Plan: make check
Differential Revision: D19713459
Pulled By: cheng-chang
fbshipit-source-id: 68cb94f4f2cc43f8b024b14755193cd45cfcad55
Summary:
I create a new branch from the branch new upsteram/master and "git merge --squash".
Maybe it will fix everything.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6420
Differential Revision: D19897152
Pulled By: zhichao-cao
fbshipit-source-id: 6575d9e3b23e360f42ee1480b43028b5fcc20136
Summary:
During recovery, multiple (un)prepared batches could exist in the same WAL record due to group commit. This breaks an assertion in `MemTableInserter::MarkBeginPrepare`.
To fix, reset unprepared_batch_ to false after `MarkEndPrepare`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6419
Differential Revision: D19896148
Pulled By: lth
fbshipit-source-id: b1a32ef88f775a0881264a18bd1a4a5b8c85eee3
Summary:
Unfortunately, it seems like mysqld reuses xids across machine restarts. When that happens, we could have something like the following happening:
```
BEGIN_PREPARE(unprepared) Put(a) END_PREPARE(xid = 1)
-- crash and recover with Put(a) rolled back as it was not prepared
BEGIN_PREPARE(prepared) Put(b) END_PREPARE(xid = 1)
COMMIT(xid = 1)
-- crash and recover with both a, b
```
To solve this, we will have to log the rollback batch into the WAL during recovery.
WritePrepared already logs the rollback batch into the WAL, if a rollback happens after prepare, so there is no problem there.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6418
Differential Revision: D19896151
Pulled By: lth
fbshipit-source-id: 2ff65ddc5fe75efd57736fed4b7cd7a109d26609
Summary:
A recent fix related to 2pc https://github.com/facebook/rocksdb/pull/6313/ writes something to WAL, but does not flush or sync. This causes assertion failure "impl->TEST_WALBufferIsEmpty()" if manual_wal_flush = true. We should fsync the entry to make sure a second power reset can recover.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6417
Test Plan: Add manual_wal_flush=true case in TransactionTest.DoubleCrashInRecovery and fix a bug in the test so that the bug can be reproduced. It passes with the fix.
Differential Revision: D19894537
fbshipit-source-id: f1e84e49e2269f583c6019743118292cd8b6598e
Summary:
The DecreaseNumBgThreads test keeps failing on Windows in AppVeyor.
It fails because it depends on a timed wait for the tasks to be dequeued from the threadpool's internal queue, but within the specified time, the task might have not been scheduled onto the newly created threads.
https://github.com/facebook/rocksdb/pull/6232 tries to fix this by waiting for longer time to let the threads scheduled.
This PR tries to fix this by replacing the timed wait with a synchronization on the task's internal conditional variable.
When the number of threads increases, instead of guessing the time needed for the task to be scheduled, it directly blocks on the conditional variable until the task starts running.
But when thread number is reduced, it still does a timed wait, but this does not lead to the flakiness now, will try to remove these timed waits in a future PR.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6393
Test Plan: Wait to see whether AppVeyor tests pass.
Differential Revision: D19890928
Pulled By: cheng-chang
fbshipit-source-id: 4e56e4addf625c98c0876e62d9d57a6f0a156f76
Summary:
Since IO Uring feature is not stable. Remove it from buck configuration.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6415
Test Plan: See internal build pass
Differential Revision: D19892988
fbshipit-source-id: 7fc01efc2af5ed707fb8e4e4674223aeb83cd5ea
Summary:
It's observed on Windows DestroyDB failed to remove the log file because the logger is still alive in sst file manager and holding a handle to the log file. This fix makes sure the logger is released before attempt to clear the database directory.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6308
Differential Revision: D19818829
Pulled By: riversand963
fbshipit-source-id: 54c3e6859aadaaba4a49b3e851b73dc35ec7dc6a
Summary:
Seems like this caused the following test failure on AppVeyor:
DBTest2.CrashInRecoveryMultipleCF
c:\projects\rocksdb\db\db_test_util.cc(107): error: DestroyDB(dbname_, options)
IO error: Failed to delete: C:\projects\rocksdb\db_tests\\testrocksdb-3112//db_test2_10791409581227174103/000013.sst: Access is denied.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6410
Test Plan: Wait to see whether the AppVeyor test passes.
Differential Revision: D19879872
Pulled By: cheng-chang
fbshipit-source-id: 59a9c55ca88566e9210c0b715ecc45a4fd9afe26
Summary:
We realized bugs related to IO Uring. Turn it off by default.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6405
Test Plan: Manually run build_tools/build_detect_platform and observe outputs.
Differential Revision: D19862792
fbshipit-source-id: 5d5e8e2762997b72a145ae59389ef3d7e4ccd060
Summary:
Unrevert the previous fix to propagate error status, and an additional fix to not treat a memtable lookup MergeInProgress status as an error.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6403
Test Plan:
Unit tests
Tried running stress tests but couldn't repro the stress failure
Differential Revision: D19846721
Pulled By: anand1976
fbshipit-source-id: 7db10cccbdc863d9b559497f0a46b608d2488ca4
Summary:
It is very useful to support direct ByteBuffers in Java. It allows to have zero memory copy and some serializers are using that directly so one do not need to create byte[] array for it.
This change also contains some fixes for Windows JNI build.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/2283
Differential Revision: D19834971
Pulled By: pdillinger
fbshipit-source-id: 44173aa02afc9836c5498c592fd1ea95b6086e8e
Summary:
Before this fix, the info_log_level passed from CreateLoggerFromOptions() will
be ignored by AutoRollLogger::logger_. This PR fixes it by setting the info log
level of logger_ during ResetLogger().
Test plan (dev server):
```
COMPILE_WITH_TSAN=1 make all && make check
make all && make check
```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6388
Differential Revision: D19828045
Pulled By: riversand963
fbshipit-source-id: e1ac7de3a2090bee53b6c667f71a11f1774163e6
Summary:
This reverts commit d70011bccc. The commit is causing some stress test failure due to unexpected Status::MergeInProgress() return for some keys.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6401
Differential Revision: D19826623
Pulled By: anand1976
fbshipit-source-id: edd634cede9cb7bdd2cb8f46e662ea709b16d2f1
Summary:
1. remove AssertEmpty because calling methods on moved objects is discouraged.
2. add a test to assert that the internal buffer is moved instead of being copied.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6399
Test Plan:
make slice_test && ./slice_test
USE_CLANG=1 make analyze
Differential Revision: D19825372
Pulled By: cheng-chang
fbshipit-source-id: 2e26f8ce5ec3edbfce067db045e80bd433e704f4
Summary:
Add a utility class `Defer` to defer the execution of a function until the Defer object goes out of scope.
Used in VersionSet:: ProcessManifestWrites as an example.
The inline comments for class `Defer` have more details.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6382
Test Plan: `make defer_test version_set_test && ./defer_test && ./version_set_test`
Differential Revision: D19797538
Pulled By: cheng-chang
fbshipit-source-id: b1a9b7306e4fd4f48ec2ab55783caa561a315f0f
Summary:
https://github.com/facebook/rocksdb/pull/6383 surfaced an issue with
`VersionSet`/`ReactiveVersionSet` and `AtomicGroupReadBuffer::AddEdit`
(which was added in https://github.com/facebook/rocksdb/pull/5411):
`AddEdit` moves the `VersionEdit` passed to it into `replay_buffer_`,
however, the client `VersionSet` classes keep using it afterwards. This
*seemed to* work before the refactoring but it really did not: since
`VersionEdit` used to have a user-declared destructor, no move
constructor/move assignment operator was generated, and the `move` in
`AddEdit` was really a copy. The patch makes the copy explicit. Note: it
should be possible to rework this logic so that we can get away
with the move but for now, this should fix the issue.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6400
Test Plan:
`make check`
`make analyze`
Differential Revision: D19824466
Pulled By: ltamasi
fbshipit-source-id: f38033967daf2a39c78dcd6e12978bafe37632b4
Summary:
In the current code base, RocksDB generate the checksum for each block and verify the checksum at usage. Current PR enable SST file checksum. After a SST file is generated by Flush or Compaction, RocksDB generate the SST file checksum and store the checksum value and checksum method name in the vs_info and MANIFEST as part for the FileMetadata.
Added the enable_sst_file_checksum to Options to enable or disable file checksum. Added sst_file_checksum to Options such that user can plugin their own SST file checksum calculate method via overriding the SstFileChecksum class. The checksum information inlcuding uint32_t checksum value and a checksum name (string). A new tool is added to LDB such that user can dump out a list of file checksum information from MANIFEST. If user enables the file checksum but does not provide the sst_file_checksum instance, RocksDB will use the default crc32checksum implemented in table/sst_file_checksum_crc32c.h
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6216
Test Plan: Added the testing case in table_test and ldb_cmd_test to verify checksum is correct in different level. Pass make asan_check.
Differential Revision: D19171461
Pulled By: zhichao-cao
fbshipit-source-id: b2e53479eefc5bb0437189eaa1941670e5ba8b87
Summary:
clang analysis shows following warning:
options/options_test.cc:1554:24: warning: The left operand of '-' is a garbage value
(file_size - 1) / readahead_size + 1);
~~~~~~~~~ ^
Explicitly initialize file_size and add an assertion to make clang analysis happy.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6398
Test Plan: Run "make analysis" and see the warning goes away.
Differential Revision: D19819662
fbshipit-source-id: 1589ea91c0c8f78242538f01448e4ad0e5fbc219
Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/6384
Test Plan: Wait and see the analysis result.
Differential Revision: D19781072
fbshipit-source-id: 75e7cb6ee619ebd289841eaabea03dd075c09d3b
Summary:
When `no_slowdown` is enabled, it returns `Status::Incomplete("Write stall")` if a stall would occur. This patch adds descriptive text for when `no_slowdown` and `low_pri` are enabled.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6396
Differential Revision: D19808978
Pulled By: cheng-chang
fbshipit-source-id: a53b0d25ed414c821a086531e0222027f925e627
Summary:
to adapt the change in ceph upstream where the bufferlist::copy() method
was removed in
c724369010
Signed-off-by: Kefu Chai <tchaikov@gmail.com>
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6395
Differential Revision: D19816815
Pulled By: zhichao-cao
fbshipit-source-id: 9210767b91af0ecdcf5dfaa3e70edcaeea55135f
Summary:
External CMAKE projects cannot add own gtest target due to CMP0002 policy. We should not add gtest target unless we build with tests.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6377
Differential Revision: D19801708
fbshipit-source-id: 662484683e8737e10397ddb0d17705da5243c4f9
Summary:
Currently, any IO errors and checksum mismatches while reading data
blocks, are being ignored by the batched MultiGet. Its only looking at
the GetContext state. Fix that.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6387
Test Plan: Add unit tests
Differential Revision: D19799819
Pulled By: anand1976
fbshipit-source-id: 46133dccbb04e64067b9fe6cda73e282203db969
Summary:
Fixed an error when compiled with -Og:
db/write_thread.cc:183:14: error: 'state' may be used uninitialized in this function [-Werror=maybe-uninitialized]
Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6275
Differential Revision: D19381755
fbshipit-source-id: a90bf3cd4a7248d9d71219e918fc6253deb97e3c
Summary:
Right, when reading from option files, no readahead is used and 8KB buffer is used. It might introduce high latency if the file system provide high latency and doesn't do readahead. Instead, introduce a readahead to the file. When calling inside DB, infer the value from options.log_readahead. Otherwise, a default 512KB readahead size is used.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6372
Test Plan: Add --log_readahead_size in db_bench. Run it with several options and observe read size from option files using strace.
Differential Revision: D19727739
fbshipit-source-id: e6d8053b0a64259abc087f1f388b9cd66fa8a583
Summary:
It's logically correct for PinnableSlice to support move semantics to transfer ownership of the pinned memory region. This PR adds both move constructor and move assignment to PinnableSlice.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6374
Test Plan:
A set of unit tests for the move semantics are added in slice_test.
So `make slice_test && ./slice_test`.
Differential Revision: D19739254
Pulled By: cheng-chang
fbshipit-source-id: f898bd811bb05b2d87384ec58b645e9915e8e0b1
Summary:
This is a bunch of small improvements to `VersionEdit`. Namely, the patch
* Makes the names and order of variables, methods, and code chunks related
to the various information elements more consistent, and adds missing
getters for the sake of completeness.
* Initializes previously uninitialized stack variables.
* Marks all getters const to improve const correctness.
* Adds in-class initializers and removes the default ctor that would
create an object with uninitialized built-in fields and call `Clear`
afterwards.
* Adds a new type alias for new files and changes the existing `typedef`
for deleted files into a type alias as well.
* Makes the helper method `DecodeNewFile4From` private.
* Switches from long-winded iterator syntax to range based loops in a
couple of places.
* Fixes a couple of assignments where an integer 0 was assigned to
boolean members.
* Fixes a getter which used to return a `const std::string` instead of
the intended `const std::string&`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6383
Test Plan: make check
Differential Revision: D19780537
Pulled By: ltamasi
fbshipit-source-id: b0b4f09fee0ec0e7c7b7a6d76bfe5346e91824d0
Summary:
Since the logic for handling IDENTITY file is now inside `NewDB`, the comment above `NewDB` is no longer relevant.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6379
Test Plan: not needed
Differential Revision: D19795440
Pulled By: cheng-chang
fbshipit-source-id: 0b1cca87ac6d92474701c46aa4c8d4d708bfa19b
Summary:
BlobDB keeps track of the mapping between SSTs and blob files using
the `OnFlushCompleted` and `OnCompactionCompleted` callbacks of
the `EventListener` interface: upon receiving a flush notification, a link
is added between the newly flushed SST and the corresponding blob file;
for compactions, links are removed for the inputs and added for the outputs.
The earlier code performed this link deletion and addition even for
trivially moved files; the new code walks through the two lists together
(in a fashion that's similar to merge sort) and skips such files.
This should mitigate https://github.com/facebook/rocksdb/issues/6338,
wherein an assertion is triggered with the earlier code when a compaction
notification for a trivial move precedes the flush notification for the
moved SST.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6381
Test Plan: make check
Differential Revision: D19773729
Pulled By: ltamasi
fbshipit-source-id: ae0f273ded061110dd9334e8fb99b0d7786650b0
Summary:
The comments are for iterators, not Cleanable.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6371
Test Plan: no need
Differential Revision: D19727527
Pulled By: cheng-chang
fbshipit-source-id: c74aeffa27ea0ce15a36ff6f9694826712cd1c70
Summary:
Several statuses were not checked during DB::Open.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6380
Test Plan: make check
Differential Revision: D19780237
Pulled By: cheng-chang
fbshipit-source-id: c8d189d20344bd1607890dd1449345bda2ef96b9
Summary:
Before this fix, atomic flush codepath may hit an assertion failure on a specific failure case.
If all flush jobs within an atomic flush succeed (they do not write to MANIFEST), but batch writing version edits to MANIFEST fails, then `cfd->imm()->RollbackMemTableFlush()` will be called twice, and the second invocation hits assertion failure `assert(m->flush_in_progress_)` since the first invocation resets the variable `flush_in_progress_` to false already.
Test plan (dev server):
```
./db_flush_test --gtest_filter=DBAtomicFlushTest/DBAtomicFlushTest.RollbackAfterFailToInstallResults
make check
```
Both must succeed.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6385
Differential Revision: D19782943
Pulled By: riversand963
fbshipit-source-id: 84e1592625e729d1b70fdc8479959387a74cb121
Summary:
In `DBSSTTest.SSTsWithLdbSuffixHandling`, some sst files are renamed to ldb files, the original intention of the test is to test that the ldb files can be loaded along with the sst files.
The original test checks this by `ASSERT_NE("NOT_FOUND", Get(Key(k)))`, but the problem is `Get(Key(k))` returns IO error due to path not found instead of NOT_FOUND, so the success of ASSERT_NE does not mean the key can be retrieved.
This PR updates the test to make sure Get(Key(k)) returns the original value.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6370
Test Plan: make db_sst_test && ./db_sst_test
Differential Revision: D19726278
Pulled By: cheng-chang
fbshipit-source-id: 993127f56457b315e669af4eeb92d6f956b7a4b7
Summary:
We see some odd errors complaining math. However, it doesn't seem that it is needed to be included. Remove the include of math.h. Just removing it from db_bench doesn't seem to break anything. Replacing sqrt from std::sqrt seems to work for histogram.cc
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6373
Test Plan: Watch Travis and appveyor to run.
Differential Revision: D19730068
fbshipit-source-id: d3ad41defcdd9f51c2da1a3673fb258f5dfacf47
Summary:
Before this PR it calls GetFileSize() once for each sst file in the DB. This can take a long time if there are be tens of thousands of sst files (e.g. in thousands of column families), and even longer if Env is talking to some remote service rather than local filesystem. This PR makes DB::Open() use sst file sizes that are already known from manifest (typically almost all files in the DB) and only call GetFileSize() for non-sst or obsolete files. Note that GetFileSize() is also called and checked against manifest in CheckConsistency(), so the calls in SstFileManagerImpl were completely redundant.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6363
Test Plan: deployed to a test cluster, looked at a dump of Env calls (from a custom instrumented Env) - no more thousands of GetFileSize()s.
Differential Revision: D19702509
Pulled By: al13n321
fbshipit-source-id: 99f8110620cb2e9d0c092dfcdbb11f3af4ff8b73
Summary:
It's a minor refactoring. We have two ReadFileToString() but they are very similar. Make the one with Env argument calls the one with FS argument instead.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6366
Test Plan: Run all existing tests
Differential Revision: D19712332
fbshipit-source-id: 5ae6fabf6355938690d95cda52afd1f39e0a7823
Summary:
Right now RocksDB gets manifest file size before recovering from it. The information is available in LogReader. Use it instead to prevent one file system call.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6369
Test Plan: Run all existing tests
Differential Revision: D19714872
fbshipit-source-id: 0144be324d403c99e3da875ea2feccc8f64e883d
Summary:
When paranoid_checks is on, DBImpl::CheckConsistency() iterates over all sst files and calls Env::GetFileSize() for each of them. As far as I could understand, this is pretty arbitrary and doesn't affect correctness - if filesystem doesn't corrupt fsynced files, the file sizes will always match; if it does, it may as well corrupt contents as well as sizes, and rocksdb doesn't check contents on open.
If there are thousands of sst files, getting all their sizes takes a while. If, on top of that, Env is overridden to use some remote storage instead of local filesystem, it can be *really* slow and overload the remote storage service. This PR adds an option to not do GetFileSize(); instead it does GetChildren() for parent directory to check that all the expected sst files are at least present, but doesn't check their sizes.
We can't just disable paranoid_checks instead because paranoid_checks do a few other important things: make the DB read-only on write errors, print error messages on read errors, etc.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6353
Test Plan: ran the added sanity check unit test. Will try it out in a LogDevice test cluster where the GetFileSize() calls are causing a lot of trouble.
Differential Revision: D19656425
Pulled By: al13n321
fbshipit-source-id: c2c421b367633033760d1f56747bad206d1fbf82
Summary:
Fix an intermittent failure in
DBErrorHandlingTest.CompactionManifestWriteError due to a race between
background error recovery and the main test thread calling
TEST_WaitForCompact().
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6367
Test Plan: Run the test using gtest_parallel
Differential Revision: D19713802
Pulled By: anand1976
fbshipit-source-id: 29e35dc26e0984fe8334c083e059f4fa1f335d68
Summary:
Right now when reading IDENTITY file, we use a very similar logic as ReadFileToString() while it does an extra file size check, which may be expensive in some file systems. There is no reason to duplicate the logic. Use ReadFileToString() instead.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6365
Test Plan: RUn all existing tests.
Differential Revision: D19709399
fbshipit-source-id: 3bac31f3b2471f98a0d2694278b41e9cd34040fe
Summary:
A relatively recent regression causes for every CF, create and open directory is called for the DB directory, unless CF has a private directory. This doesn't scale well with large number of column families.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6358
Test Plan: Run all existing tests and see it pass. strace with db_bench --num_column_families and observe it doesn't open directory for number of column families.
Differential Revision: D19675141
fbshipit-source-id: da01d9216f1dae3f03d4064fbd88ce71245bd9be
Summary:
MultiDBCompactionError fails when it verifies the number of files on level 0 and level 1 without waiting for compaction to finish.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6266
Differential Revision: D19701639
Pulled By: riversand963
fbshipit-source-id: e96d511bcde705075f073e0b550cebcd2ecfccdc
Summary:
This is a redesign of the API for RocksJava comparators with the aim of improving performance. It also simplifies the class hierarchy.
**NOTE**: This breaks backwards compatibility for existing 3rd party Comparators implemented in Java... so we need to consider carefully which release branches this goes into.
Previously when implementing a comparator in Java the developer had a choice of subclassing either `DirectComparator` or `Comparator` which would use direct and non-direct byte-buffers resepectively (via `DirectSlice` and `Slice`).
In this redesign there we have eliminated the overhead of using the Java Slice classes, and just use `ByteBuffer`s. The `ComparatorOptions` supplied when constructing a Comparator allow you to choose between direct and non-direct byte buffers by setting `useDirect`.
In addition, the `ComparatorOptions` now allow you to choose whether a ByteBuffer is reused over multiple comparator calls, by setting `maxReusedBufferSize > 0`. When buffers are reused, ComparatorOptions provides a choice of mutex type by setting `useAdaptiveMutex`.
---
[JMH benchmarks previously indicated](https://github.com/facebook/rocksdb/pull/6241#issue-356398306) that the difference between C++ and Java for implementing a comparator was ~7x slowdown in Java.
With these changes, when reusing buffers and guarding access to them via mutexes the slowdown is approximately the same. However, these changes offer a new facility to not reuse mutextes, which reduces the slowdown to ~5.5x in Java. We also offer a `thread_local` mechanism for reusing buffers, which reduces slowdown to ~5.2x in Java (closes https://github.com/facebook/rocksdb/pull/4425).
These changes also form a good base for further optimisation work such as further JNI lookup caching, and JNI critical.
---
These numbers were captured without jemalloc. With jemalloc, the performance improves for all tests, and the Java slowdown reduces to between 4.8x and 5.x.
```
ComparatorBenchmarks.put native_bytewise thrpt 25 124483.795 ± 2032.443 ops/s
ComparatorBenchmarks.put native_reverse_bytewise thrpt 25 114414.536 ± 3486.156 ops/s
ComparatorBenchmarks.put java_bytewise_non-direct_reused-64_adaptive-mutex thrpt 25 17228.250 ± 1288.546 ops/s
ComparatorBenchmarks.put java_bytewise_non-direct_reused-64_non-adaptive-mutex thrpt 25 16035.865 ± 1248.099 ops/s
ComparatorBenchmarks.put java_bytewise_non-direct_reused-64_thread-local thrpt 25 21571.500 ± 871.521 ops/s
ComparatorBenchmarks.put java_bytewise_direct_reused-64_adaptive-mutex thrpt 25 23613.773 ± 8465.660 ops/s
ComparatorBenchmarks.put java_bytewise_direct_reused-64_non-adaptive-mutex thrpt 25 16768.172 ± 5618.489 ops/s
ComparatorBenchmarks.put java_bytewise_direct_reused-64_thread-local thrpt 25 23921.164 ± 8734.742 ops/s
ComparatorBenchmarks.put java_bytewise_non-direct_no-reuse thrpt 25 17899.684 ± 839.679 ops/s
ComparatorBenchmarks.put java_bytewise_direct_no-reuse thrpt 25 22148.316 ± 1215.527 ops/s
ComparatorBenchmarks.put java_reverse_bytewise_non-direct_reused-64_adaptive-mutex thrpt 25 11311.126 ± 820.602 ops/s
ComparatorBenchmarks.put java_reverse_bytewise_non-direct_reused-64_non-adaptive-mutex thrpt 25 11421.311 ± 807.210 ops/s
ComparatorBenchmarks.put java_reverse_bytewise_non-direct_reused-64_thread-local thrpt 25 11554.005 ± 960.556 ops/s
ComparatorBenchmarks.put java_reverse_bytewise_direct_reused-64_adaptive-mutex thrpt 25 22960.523 ± 1673.421 ops/s
ComparatorBenchmarks.put java_reverse_bytewise_direct_reused-64_non-adaptive-mutex thrpt 25 18293.317 ± 1434.601 ops/s
ComparatorBenchmarks.put java_reverse_bytewise_direct_reused-64_thread-local thrpt 25 24479.361 ± 2157.306 ops/s
ComparatorBenchmarks.put java_reverse_bytewise_non-direct_no-reuse thrpt 25 7942.286 ± 626.170 ops/s
ComparatorBenchmarks.put java_reverse_bytewise_direct_no-reuse thrpt 25 11781.955 ± 1019.843 ops/s
```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6252
Differential Revision: D19331064
Pulled By: pdillinger
fbshipit-source-id: 1f3b794e6a14162b2c3ffb943e8c0e64a0c03738
Manuel Ung