Summary:
Gets `Statistics` from the options associated with the `DB` undergoing backup, and populates new ticker stats with the thread-local `IOContext` read/write counters for the threads doing backup work.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8819
Reviewed By: pdillinger
Differential Revision: D30779238
Pulled By: ajkr
fbshipit-source-id: 75ccafc355f90906df5cf80367f7245b985772d8
Summary:
- Clarified some comments on compatibility for adding new ticker stats
- Added read I/O stats for `VerifyChecksum()` and `VerifyFileChecksums()` APIs
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8741
Test Plan: new unit test
Reviewed By: zhichao-cao
Differential Revision: D30708578
Pulled By: ajkr
fbshipit-source-id: d06b961f7e199ae92c266b683e39870aa8f63449
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:
Some FIFO users want to keep the data for longer, but the old data is rarely accessed. This feature allows users to configure FIFO compaction so that data older than a threshold is moved to a warm storage tier.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8310
Test Plan: Add several unit tests.
Reviewed By: ajkr
Differential Revision: D28493792
fbshipit-source-id: c14824ea634814dee5278b449ab5c98b6e0b5501
Summary:
**Summary**:
2 new statistics counters are added to RocksDB: `MEMTABLE_PAYLOAD_BYTES_AT_FLUSH` and `MEMTABLE_GARBAGE_BYTES_AT_FLUSH`. The former tracks how many raw bytes of useful data are present on the memtable at flush time, whereas the latter is tracks how many of these raw bytes are considered garbage, meaning that they ended up not being imported on the SSTables resulting from the flush operations.
**Unit test**: run `make db_flush_test -j$(nproc); ./db_flush_test` to run the unit test.
This executable includes 3 tests, that test support and correct stat calculations for workloads with inserts, deletes, and DeleteRanges. The parameters are set such that the workloads are performed on a single memtable, and a single SSTable is created as a result of the flush operation. The flush operation is manually called in the test file. The tests verify that the values of these 2 statistics counters introduced in this PR can be exactly predicted, showing that we have a full understanding of the underlying operations.
**Performance testing**:
`./db_bench -statistics -benchmarks=fillrandom -num=10000000` repeated 10 times.
Timing done using "date" function in a bash script.
_Results_:
Original Rocksdb fork: mean 66.6 sec, std 1.18 sec.
This feature branch: mean 67.4 sec, std 1.35 sec.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8411
Reviewed By: akankshamahajan15
Differential Revision: D29150629
Pulled By: bjlemaire
fbshipit-source-id: 7b3c2e86d50c6aa34fa50fd134282eacb543a5b1
Summary:
Added `TableProperties::{fast,slow}_compression_estimated_data_size`.
These properties are present in block-based tables when
`ColumnFamilyOptions::sample_for_compression > 0` and the necessary
compression library is supported when the file is generated. They
contain estimates of what `TableProperties::data_size` would be if the
"fast"/"slow" compression library had been used instead. One
limitation is we do not record exactly which "fast" (ZSTD or Zlib)
or "slow" (LZ4 or Snappy) compression library produced the result.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8139
Test Plan:
- new unit test
- ran `db_bench` with `sample_for_compression=1`; verified the `data_size` property matches the `{slow,fast}_compression_estimated_data_size` when the same compression type is used for the output file compression and the sampled compression
Reviewed By: riversand963
Differential Revision: D27454338
Pulled By: ajkr
fbshipit-source-id: 9529293de93ddac7f03b2e149d746e9f634abac4
Summary:
Add statistics and info log for error handler: counters for bg error, bg io error, bg retryable io error, auto resume, auto resume total retry, and auto resume sucess; Histogram for auto resume retry count in each recovery call.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8050
Test Plan: make check and add test to error_handler_fs_test
Reviewed By: anand1976
Differential Revision: D26990565
Pulled By: zhichao-cao
fbshipit-source-id: 49f71e8ea4e9db8b189943976404205b56ab883f
Summary:
Allows adding event listeners in RocksJava.
* Adds listeners getter and setter in `Options` and `DBOptions` classes.
* Adds `EventListener` Java interface and base class for implementing custom event listener callbacks - `AbstractEventListener`, which has an underlying native callback class implementing C++ `EventListener` class.
* `AbstractEventListener` class has mechanism for selectively enabling its callback methods in order to prevent invoking Java method if it is not implemented. This decreases performance cost in case only subset of event listener callback methods is needed - the JNI code for remaining "no-op" callbacks is not executed.
* The code is covered by unit tests in `EventListenerTest.java`, there are also tests added for setting/getting listeners field in `OptionsTest.java` and `DBOptionsTest.java`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/7425
Reviewed By: pdillinger
Differential Revision: D24063390
Pulled By: jay-zhuang
fbshipit-source-id: 508c359538983d6b765e70d9989c351794a944ee
Summary:
Add following stats for MultiGet in Histogram to get more insight on MultiGet.
1. Number of index and filter blocks read from file as part of MultiGet
request per level.
2. Number of data blocks read from file per level.
3. Number of SST files loaded from file system per level.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/7366
Reviewed By: anand1976
Differential Revision: D24127040
Pulled By: akankshamahajan15
fbshipit-source-id: e63a003056b833729b277edc0639c08fb432756b
Summary:
Adds compaction statistics (total bytes read and written) for compactions that occur for delete-triggered, periodic, and TTL compaction reasons.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/7165
Test Plan:
TTL and periodic can be checked by runnning db_bench with the options activated:
/db_bench --benchmarks="fillrandom,stats" --statistics --num=10000000 -base_background_compactions=16 -periodic_compaction_seconds=1
./db_bench --benchmarks="fillrandom,stats" --statistics --num=10000000 -base_background_compactions=16 -fifo_compaction_ttl=1
Setting the time to one second causes non-zero bytes read/written for those compaction reasons. Disabling them or setting them to times longer than the test run length causes the stats to return to zero as expected.
Delete-triggered compaction counting is tested in DBTablePropertiesTest.DeletionTriggeredCompactionMarking
Reviewed By: ajkr
Differential Revision: D22693050
Pulled By: akabcenell
fbshipit-source-id: d15cef4d94576f703015c8942d5f0d492f69401d
Summary:
The methods in convenience.h are used to compare/convert objects to/from strings. There is a mishmash of parameters in use here with more needed in the future. This PR replaces those parameters with a single structure.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6389
Reviewed By: siying
Differential Revision: D21163707
Pulled By: zhichao-cao
fbshipit-source-id: f807b4cc7e2b0af3871536b69546b2604dfa81bd
Summary:
When dynamically linking two binaries together, different builds of RocksDB from two sources might cause errors. To provide a tool for user to solve the problem, the RocksDB namespace is changed to a flag which can be overridden in build time.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6433
Test Plan: Build release, all and jtest. Try to build with ROCKSDB_NAMESPACE with another flag.
Differential Revision: D19977691
fbshipit-source-id: aa7f2d0972e1c31d75339ac48478f34f6cfcfb3e
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:
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
Summary:
if read_options.snapshot is not set, ::Get will take the last sequence number after taking a super-version and uses that as the sequence number. Theoretically max_eviceted_seq_ could advance this sequence number. This could lead ::IsInSnapshot that will be invoked by the ReadCallback to notice the absence of the snapshot. In this case, the ReadCallback should have passed a non-value to snap_released so that it could be set by the ::IsInSnapshot. The patch does that, and adds a unit test to verify it.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5664
Differential Revision: D16614033
Pulled By: maysamyabandeh
fbshipit-source-id: 06fb3fd4aacd75806ed1a1acec7961f5d02486f2
Summary:
The first key is used to defer reading the data block until this file gets to the top of merging iterator's heap. For short range scans, most files never make it to the top of the heap, so this change can reduce read amplification by a lot sometimes.
Consider the following workload. There are a few data streams (we'll be calling them "logs"), each stream consisting of a sequence of blobs (we'll be calling them "records"). Each record is identified by log ID and a sequence number within the log. RocksDB key is concatenation of log ID and sequence number (big endian). Reads are mostly relatively short range scans, each within a single log. Writes are mostly sequential for each log, but writes to different logs are randomly interleaved. Compactions are disabled; instead, when we accumulate a few tens of sst files, we create a new column family and start writing to it.
So, a typical sst file consists of a few ranges of blocks, each range corresponding to one log ID (we use FlushBlockPolicy to cut blocks at log boundaries). A typical read would go like this. First, iterator Seek() reads one block from each sst file. Then a series of Next()s move through one sst file (since writes to each log are mostly sequential) until the subiterator reaches the end of this log in this sst file; then Next() switches to the next sst file and reads sequentially from that, and so on. Often a range scan will only return records from a small number of blocks in small number of sst files; in this case, the cost of initial Seek() reading one block from each file may be bigger than the cost of reading the actually useful blocks.
Neither iterate_upper_bound nor bloom filters can prevent reading one block from each file in Seek(). But this PR can: if the index contains first key from each block, we don't have to read the block until this block actually makes it to the top of merging iterator's heap, so for short range scans we won't read any blocks from most of the sst files.
This PR does the deferred block loading inside value() call. This is not ideal: there's no good way to report an IO error from inside value(). As discussed with siying offline, it would probably be better to change InternalIterator's interface to explicitly fetch deferred value and get status. I'll do it in a separate PR.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5289
Differential Revision: D15256423
Pulled By: al13n321
fbshipit-source-id: 750e4c39ce88e8d41662f701cf6275d9388ba46a
Summary:
Depending on the config, manual compaction (leveled compaction style) does following compactions:
L0->L1
L1->L2
...
Ln-1 -> Ln
Ln -> Ln
The final Ln -> Ln compaction is partly unnecessary as it recompacts all the files that were just generated by the Ln-1 -> Ln. We should avoid recompacting such files. This rule should be applied to Lmax only.
Resolves issue https://github.com/facebook/rocksdb/issues/4995
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5138
Differential Revision: D14940106
Pulled By: miasantreble
fbshipit-source-id: 8d3cf5507a17e76f3333cfd4bac5256d005636e5
Summary:
This is my latest round of changes to add missing items to RocksJava. More to come in future PRs.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4833
Differential Revision: D14152266
Pulled By: sagar0
fbshipit-source-id: d6cff67e26da06c131491b5cf6911a8cd0db0775
Summary:
This PR adds public `GetStatsHistory` API to retrieve stats history in the form of an std map. The key of the map is the timestamp in microseconds when the stats snapshot is taken, the value is another std map from stats name to stats value (stored in std string). Two DBOptions are introduced: `stats_persist_period_sec` (default 10 minutes) controls the intervals between two snapshots are taken; `max_stats_history_count` (default 10) controls the max number of history snapshots to keep in memory. RocksDB will stop collecting stats snapshots if `stats_persist_period_sec` is set to 0.
(This PR is the in-memory part of https://github.com/facebook/rocksdb/pull/4535)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4748
Differential Revision: D13961471
Pulled By: miasantreble
fbshipit-source-id: ac836d401ecb84ea92216bf9966f969dedf4ad04
Summary:
Expose common stats min,max,count,sum via statistics JNI. These stats are not fully exposed on the Java side as is, but are available on the native side.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4742
Differential Revision: D13403766
Pulled By: ajkr
fbshipit-source-id: 5b70f7bd3fb7490aab73dcbd09f13490fce5c773
Summary:
Updating the `HistogramType.java` and `TickerType.java` to expose and correct metrics for statistics callbacks.
Moved `NO_ITERATOR_CREATED` to the proper stat name and deprecated `NO_ITERATORS`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4733
Differential Revision: D13466936
Pulled By: sagar0
fbshipit-source-id: a58d1edcc07c7b68c3525b1aa05828212c89c6c7
Summary:
Added back `NO_ITERATORS` and moved `NO_ITERATOR_CREATED` to the end of `toCppTickers`.
This is a leftover fix which is needed in addition to a138e351bc to correctly convert java tickers to c++ tickers. a138e351bc only updated `toJavaTickerType` but both `toJavaTickerType` and `toCppTickers` need to be changed.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4719
Differential Revision: D13208847
Pulled By: sagar0
fbshipit-source-id: 53a42f3d6ffe04034acfde972d73040b92b4c1af
Summary:
- Added back the `NO_ITERATORS` that was removed in 5945e16dfc.
- Marked it as deprecated since it is no longer populated, but kept for API compatibility.
- Made sure the new tickers, `NO_ITERATOR_CREATED` and `NO_ITERATOR_DELETED`, are appended at the end of the enum, in case people are relying on the int values.
The change where `NO_ITERATOR_CREATED` and `NO_ITERATOR_DELETED` were introduced is unreleased so I believe it is ok to change their ordering.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4701
Differential Revision: D13142887
Pulled By: ajkr
fbshipit-source-id: 29a336ce5b46632ce50ad42ccc4a29013f71d6d6
Summary:
Currently, `Statistics` can record tick by `recordTick()` whose second parameter is an `uint64_t`.
That means tick can only increase.
If we want to reduce tick, we have to work around like `RecordTick(statistics_, NO_ITERATORS, uint64_t(-1));`.
That's kind of a hack.
So, this PR divide `NO_ITERATORS` into two counters `NO_ITERATOR_CREATED` and `NO_ITERATOR_DELETE`, making the counters increase only.
Fixes#3013 .
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4498
Differential Revision: D10395010
Pulled By: sagar0
fbshipit-source-id: cfb523b22a37411c794b4e9da090f1ae30293db2
Summary:
Closes https://github.com/facebook/rocksdb/issues/4195
CompactRangeOptions are available the CPP API, but not in the Java API. This PR adds CompactRangeOptions to the Java API and adds an overloaded compactRange() method. See https://github.com/facebook/rocksdb/issues/4195 for the original discussion.
This change supports all fields of CompactRangeOptions, including the required enum converters in the JNI portal.
Significant changes:
- Make CompactRangeOptions available in the compactRange() for Java.
- Deprecate other compactRange() methods that have individual option params, like in the CPP code.
- Migrate rocksdb_compactrange_helper() to CompactRangeOptions.
- Add Java unit tests for CompactRangeOptions.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4220
Differential Revision: D9380007
Pulled By: sagar0
fbshipit-source-id: 6af6c334f221427f1997b33fb24c3986b092fed6
Summary:
Fixes#3391.
This change adds a `DeleteRange` method to `SstFileWriter` and adds
support for ingesting SSTs with range deletion tombstones. This is
important for applications that need to atomically ingest SSTs while
clearing out any existing keys in a given key range.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/3778
Differential Revision: D8821836
Pulled By: anand1976
fbshipit-source-id: ca7786c1947ff129afa703dab011d524c7883844
Summary:
Exposes BackupEngine::CreateNewBackupWithMetadata and BackupInfo metadata to the Java API.
Full disclaimer, I'm not familiar with JNI stuff, so I might have forgotten something (hopefully no memory leaks!). I also tried to find contributing guidelines but didn't see any, but I hope the PR style is consistent with the rest of the code base.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4111
Differential Revision: D8811180
Pulled By: ajkr
fbshipit-source-id: e38b3e396c7574328c2a1a0e55acc8d092b6a569
Summary:
1. Add a new ticker stat rocksdb.number.multiget.keys.found to track the
number of keys successfully read
2. Update rocksdb.memtable.hit/miss in DBImpl::MultiGet(). It was being done in
DBImpl::GetImpl(), but not MultiGet
Closes https://github.com/facebook/rocksdb/pull/3730
Differential Revision: D7677364
Pulled By: anand1976
fbshipit-source-id: af22bd0ef8ddc5cf2b4244b0a024e539fe48bca5
Summary:
This PR comments out the rest of the unused arguments which allow us to turn on the -Wunused-parameter flag. This is the second part of a codemod relating to https://github.com/facebook/rocksdb/pull/3557.
Closes https://github.com/facebook/rocksdb/pull/3662
Differential Revision: D7426121
Pulled By: Dayvedde
fbshipit-source-id: 223994923b42bd4953eb016a0129e47560f7e352
Summary:
Add a new histogram stat called rocksdb.db.flush.micros for memtable
flush
Closes https://github.com/facebook/rocksdb/pull/3269
Differential Revision: D6559496
Pulled By: anand1976
fbshipit-source-id: f5c771ba2568630458751795e8c37a493ff9b14d
Summary:
This diff adds a new ticker stat, NUMBER_ITER_SKIP, to count the
number of internal keys skipped during iteration. Keys can be skipped
due to deletes, or lower sequence number, or higher sequence number
than the one requested.
Also, fix the issue when StatisticsData is naturally aligned on cacheline boundary,
padding becomes a zero size array, which the Windows compiler doesn't
like. So add a cacheline worth of padding in that case to keep it happy.
We cannot conditionally add padding as gcc doesn't allow using sizeof
in preprocessor directives.
Closes https://github.com/facebook/rocksdb/pull/3177
Differential Revision: D6353897
Pulled By: anand1976
fbshipit-source-id: 441d5a09af9c4e22e7355242dfc0c7b27aa0a6c2
Summary:
Java's `Status.SubCode` was out of sync with `include/rocksdb/status.h:SubCode`.
When running out of disc space this led to an `IllegalArgumentException` because of an invalid status code, rather than just returning the corresponding status code without an exception.
I added the missing status codes.
By this, we keep the behaviour of throwing an `IllegalArgumentException` in case of newly added status codes that are defined in C but not in Java.
We could think of an alternative strategy: add in Java another code "UnknownCode" which acts as a catch-all for all those status codes that are not yet mirrored from C to Java. This approach would never throw an exception but simply return a non-OK status-code.
I think the current approach of throwing an Exception in case of a C/Java inconsistency is fine, but if you have some opinion on the alternative strategy, then feel free to comment here.
Closes https://github.com/facebook/rocksdb/pull/3050
Differential Revision: D6129682
Pulled By: sagar0
fbshipit-source-id: f2bf44caad650837cffdcb1f93eb793b43580c66
Summary:
This PR also includes some cleanup, bugfixes and refactoring of the Java API. However these are really pre-cursors on the road to CompactionFilterFactory support.
Closes https://github.com/facebook/rocksdb/pull/1241
Differential Revision: D6012778
Pulled By: sagar0
fbshipit-source-id: 0774465940ee99001a78906e4fed4ef57068ad5c
Jay Zhuang