Summary:
We've got a crash with this stack trace:
Program terminated with signal SIGTRAP, Trace/breakpoint trap.
#0 0x00007fc85f2f4009 in raise () from /usr/local/fbcode/gcc-4.9-glibc-2.20-fb/lib/libpthread.so.0
#1 0x00000000005c8f61 in facebook::logdevice::handle_sigsegv(int) () at logdevice/server/sigsegv.cpp:159
#2 0x00007fc85f2f4150 in <signal handler called> () at /usr/local/fbcode/gcc-4.9-glibc-2.20-fb/lib/libpthread.so.0
#3 0x00000000031ed80c in rocksdb::NewReadaheadRandomAccessFile() at util/file_reader_writer.cc:383
#4 0x00000000031ed80c in rocksdb::NewReadaheadRandomAccessFile() at util/file_reader_writer.cc:472
#5 0x00000000031558e7 in rocksdb::TableCache::GetTableReader() at db/table_cache.cc:99
#6 0x0000000003156329 in rocksdb::TableCache::NewIterator() at db/table_cache.cc:198
#7 0x0000000003166568 in rocksdb::VersionSet::MakeInputIterator() at db/version_set.cc:3345
#8 0x000000000324a94f in rocksdb::CompactionJob::ProcessKeyValueCompaction(rocksdb::CompactionJob::SubcompactionState*) () at db/compaction_job.cc:650
#9 0x000000000324c2f6 in rocksdb::CompactionJob::Run() () at db/compaction_job.cc:530
#10 0x00000000030f5ae5 in rocksdb::DBImpl::BackgroundCompaction() at db/db_impl.cc:3269
#11 0x0000000003108d36 in rocksdb::DBImpl::BackgroundCallCompaction(void*) () at db/db_impl.cc:2970
#12 0x00000000029a2a9a in facebook::logdevice::RocksDBEnv::callback(void*) () at logdevice/server/locallogstore/RocksDBEnv.cpp:26
#13 0x00000000029a2a9a in facebook::logdevice::RocksDBEnv::callback(void*) () at logdevice/server/locallogstore/RocksDBEnv.cpp:30
#14 0x00000000031e7521 in rocksdb::ThreadPool::BGThread() at util/threadpool.cc:230
#15 0x00000000031e7663 in rocksdb::BGThreadWrapper(void*) () at util/threadpool.cc:254
#16 0x00007fc85f2ea7f1 in start_thread () at /usr/local/fbcode/gcc-4.9-glibc-2.20-fb/lib/libpthread.so.0
#17 0x00007fc85e8fb46d in clone () at /usr/local/fbcode/gcc-4.9-glibc-2.20-fb/lib/libc.so.6
From looking at the code, probably what happened is this:
- `TableCache::GetTableReader()` called `Env::NewRandomAccessFile()`, which dispatched to a `PosixEnv::NewRandomAccessFile()`, where probably an `open()` call failed, so the `NewRandomAccessFile()` left a nullptr in the resulting file,
- `TableCache::GetTableReader()` called `NewReadaheadRandomAccessFile()` with that `nullptr` file,
- it tried to call file's method and crashed.
This diff is a trivial fix to this crash.
Test Plan: `make -j check`
Reviewers: sdong, andrewkr, IslamAbdelRahman
Reviewed By: IslamAbdelRahman
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D62451
Summary:
We used to allow insert into full block cache as long as `strict_capacity_limit=false`. This diff further restrict insert to full cache if caller don't intent to hold handle to the cache entry after insert.
Hope this diff fix the assertion failure with db_stress: https://our.intern.facebook.com/intern/sandcastle/log/?instance_id=211853102&step_id=2475070014
db_stress: util/lru_cache.cc:278: virtual void rocksdb::LRUCacheShard::Release(rocksdb::Cache::Handle*): Assertion `lru_.next == &lru_' failed.
The assertion at lru_cache.cc:278 can fail when an entry is inserted into full cache and stay in LRU list.
Test Plan:
make all check
Reviewers: IslamAbdelRahman, lightmark, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D62325
Summary:
Add option to block based table to insert index/filter blocks to block cache with priority. Combined with LRUCache with high_pri_pool_ratio, we can reserved space for index/filter blocks, make them less likely to be evicted.
Depends on D61977.
Test Plan: See unit test.
Reviewers: lightmark, IslamAbdelRahman, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba, march, leveldb
Differential Revision: https://reviews.facebook.net/D62241
Summary: Update SstFileWriter to use user TablePropertiesCollectors that are passed in Options
Test Plan: unittests
Reviewers: sdong
Reviewed By: sdong
Subscribers: jkedgar, andrewkr, hermanlee4, dhruba, yoshinorim
Differential Revision: https://reviews.facebook.net/D62253
Summary: 1. Range Deletion Tombstone structure 2. Modify Add() in table_builder to make it usable for adding range del tombstones 3. Expose NewTombstoneIterator() API in table_reader
Test Plan: table_test.cc (now BlockBasedTableBuilder::Add() only accepts InternalKey. I make table_test only pass InternalKey to BlockBasedTableBuidler. Also test writing/reading range deletion tombstones in table_test )
Reviewers: sdong, IslamAbdelRahman, lightmark, andrewkr
Reviewed By: andrewkr
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D61473
Summary:
Added 2 statistics in compaction job statistics, to
identify if single deletes are not meeting a matching key
(fallthrough) or single deletes are meeting a merge, delete or
another single delete (i.e. not the expected case of put).
Test Plan: Tested the statistics using write_stress and compaction_job_stats_test
Reviewers: sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D61749
Summary:
Add API to WriteBatch to store range deletions in its buffer
which are later added to memtable. In the WriteBatch buffer, a range
deletion is encoded as "<optype><CF ID (optional)><begin key><end key>".
With this diff, the range tombstones are stored inline with the data in
the memtable. It's useful for now because the test cases rely on the
data being accessible via memtable. My next step is to store range
tombstones in a separate area in the memtable.
Test Plan: unit tests
Reviewers: IslamAbdelRahman, sdong, wanning
Reviewed By: wanning
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D61401
Summary: Fix the test by releasing the last snapshot
Test Plan: run the test under valgrind
Reviewers: andrewkr, yiwu, lightmark, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D62091
Summary: "Batch" is ambiguous in this context. It can mean "write batch" or commit group. Change it to commit group to be clear.
Test Plan: Build
Reviewers: MarkCallaghan, yhchiang, IslamAbdelRahman
Reviewed By: IslamAbdelRahman
Subscribers: leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D62055
Summary:
This diff update ForwardIterator to support pinning keys and values, which will allow DBIter to take advantage of that and eliminate memcpy when executing merge operators
This diff is stacked on D61305
Test Plan:
existing tests (updated them to test tailing iterator)
new test
Reviewers: andrewkr, yhchiang, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D60009
Summary:
This diff include these simple change
- Rename ReleasePinnedIterators to ReleasePinnedData
- Rename PinIteratorIfNeeded to PinIterator
- Use std::vector directly in PinnedIteratorsManager instead of std::unique_ptr<std::vector>
- Generalize PinnedIteratorsManager by adding PinPtr which can pin any pointer
Test Plan: existing tests
Reviewers: sdong, yiwu, andrewkr
Reviewed By: andrewkr
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D61305
Summary: Background sleeping tasks may conflict with test cleaning up. Wait for the sleeping tasks to finish before ending the test.
Test Plan: Run these tests.
Reviewers: andrewkr, yiwu
Reviewed By: yiwu
Subscribers: leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D61827
Summary: With read_options.background_purge_on_iterator_cleanup=true, File deletion and closing can still happen in forward iterator, or WAL file closing. Cover those cases too.
Test Plan: I am adding unit tests.
Reviewers: andrewkr, IslamAbdelRahman, yiwu
Reviewed By: yiwu
Subscribers: leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D61503
Summary:
If we have total number of sorted runs greater than level0_file_num_compaction_trigger, Universal compaction will always issue a compaction
even if the number of sorted runs that are not being compacted is less than level0_file_num_compaction_trigger.
This diff changes this behaviour to relay on the `number of sorted runs not being compacted` instead of `total number of sorted runs`
Test Plan: New unit test
Reviewers: sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D61533
* Added check_snapshot option in the DB's AddFile function
* change check_snapshot to skip_snapshot_check
* add unit test for skip_snapshot_check
* Add skip_snapshot_check comment
Summary: Explicitly flush two times to generate two sst files.
Test Plan: run the test.
Reviewers: sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D61671
Summary: The test `ObsoleteFiles` failed occasionally on slow device. This problem appears on Travis CI several times. The reason is that we did not wait until compaction jobs are finished in the test, while in slower device the background jobs take longer time to finish.
Test Plan: Pass existing tests.
Reviewers: yiwu, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D61479
Summary:
My understanding is that the purpose of write stall triggers are to wait for auto-compaction to catch up. Without auto-compaction, we don't need to stall writes.
Also with this diff, flush/compaction conditions are recalculated on dynamic option change. Previously the conditions are recalculate only when write stall options are changed.
Test Plan: See the new test. Removed two tests that are no longer valid.
Reviewers: IslamAbdelRahman, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D61437
Summary:
patch for diff https://reviews.facebook.net/D58587
Also change StopWatch class to add a fifth param named overwrite which decides whether to overwrite *elapse or add on it.
Test Plan: make all check -j64
Reviewers: sdong, IslamAbdelRahman
Reviewed By: IslamAbdelRahman
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D61239
Summary: MyRocks is adding support for the user of the SstFileWriter which needs a comparator. It would be more convenient to get the comparator from the column family (which already has to have it) than to have caller keep track of it.
Test Plan: Standard tests (adding one for the new method)
Reviewers: IslamAbdelRahman, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D61155
Summary:
DBTest.CompressionStatsTest on non_shm test where the storage device is slow
DBTest.CompressionStatsTest assumes that a flush happens to check the number of compressed blocks.
This is not always true if the Flush is slow, make the test more deterministic by forcing a flush before doing the check
Test Plan: Run the test locally
Reviewers: andrewkr, yiwu, lightmark, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D61317
Summary: regression tests to make sure seek keys not in domain would not fail assertion
Test Plan:
```
[gzh@dev6163.prn2 ~/local/rocksdb] ./prefix_test --gtest_filter=SamePrefixTest.*
/tmp/rocksdbtest-112628/prefix_test
Note: Google Test filter = SamePrefixTest.*
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from SamePrefixTest
[ RUN ] SamePrefixTest.InDomainTest
[ OK ] SamePrefixTest.InDomainTest (211 ms)
[----------] 1 test from SamePrefixTest (211 ms total)
[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (211 ms total)
```
Reviewers: andrewkr, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D61161
Summary: Extend the option memtable_prefix_bloom_huge_page_tlb_size from just putting memtable bloom filter to huge page to memtable itself too.
Test Plan: Run all existing tests.
Reviewers: IslamAbdelRahman, yhchiang, andrewkr
Reviewed By: andrewkr
Subscribers: leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D60513
Summary: We may wrongly drop delete operation if we pick a file with the entry to be delete, the put entry of the same user key is in the next file in the level, and the next file is not picked. We expand compaction inputs for output level too.
Test Plan: Add unit tests that reproduct the bug of dropping delete entry. Change compaction_picker_test to assert the new behavior.
Reviewers: IslamAbdelRahman, igor
Reviewed By: igor
Subscribers: leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D61173
Summary: old typos with FILTER/INDEX_CACHE
Test Plan: still pass this unit test
Reviewers: andrewkr
Reviewed By: andrewkr
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D61185
Summary:
MergeContext::copied_operands contain strings that MergeContext::operand_list_ Slices point to
It's possible that when MergeContext::copied_operands grow, these strings are moved and there place in memory is changed, this will cause MergeContext::operand_list_ to point to invalid memory.
fix this problem by using unique_ptr<string> instead of string
Test Plan: run tests under mac/clang
Reviewers: sdong, yiwu
Reviewed By: yiwu
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D61023
Summary: The test is flaky on Travis in osx environment. The background flush the test wanting to block can run behind the L2 manual compaction, making the test actually blocking the L2 compaction and won't able to proceed.
Test Plan: Test run on travis
Reviewers: kradhakrishnan, sdong, andrewkr, IslamAbdelRahman
Reviewed By: IslamAbdelRahman
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D61101
Summary: RocksDB lite don't support dynamic options. Disable the two test from lite build, and assert `SetOptions` should return `status::OK`.
Test Plan: Run the db_options test under lite build and normal build.
Reviewers: sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D61119
Summary:
Stale log files can be deleted out of order. This can happen for various reasons. One of the reason is that no data is ever inserted to a column family and we have an optimization to update its log number, but not all the old log files are cleaned up (the case shown in the unit tests added). It can also happen when we simply delete multiple log files out of order.
This causes data corruption because we simply increase seqID after processing the next row and we may end up with writing data with smaller seqID than what is already flushed to memtables.
In DB recovery, for the oldest files we are replaying, if there it contains no data for any column family, we ignore the sequence IDs in the file.
Test Plan: Add two unit tests that fail without the fix.
Reviewers: IslamAbdelRahman, igor, yiwu
Reviewed By: yiwu
Subscribers: hermanlee4, yoshinorim, leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D60891
Summary: Multiput atomiciy is broken across multiple column families if we don't sync WAL before flushing one column family. The WAL file may contain a write batch containing writes to a key to the CF to be flushed and a key to other CF. If we don't sync WAL before flushing, if machine crashes after flushing, the write batch will only be partial recovered. Data to other CFs are lost.
Test Plan: Add a new unit test which will fail without the diff.
Reviewers: yhchiang, IslamAbdelRahman, igor, yiwu
Reviewed By: yiwu
Subscribers: yiwu, leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D60915
Summary: Comment out assertion of number of table files from lite build.
Test Plan:
OPT=-DROCKSDB_LITE make check
Reviewers: lightmark
Reviewed By: lightmark
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D60999
Summary:
Fix flush not being commit while writing manifest, which is a recent bug introduced by D60075.
The issue:
# Options.max_background_flushes > 1
# Background thread A pick up a flush job, flush, then commit to manifest. (Note that mutex is released before writing manifest.)
# Background thread B pick up another flush job, flush. When it gets to `MemTableList::InstallMemtableFlushResults`, it notices another thread is commiting, so it quit.
# After the first commit, thread A doesn't double check if there are more flush result need to commit, leaving the second flush uncommitted.
Test Plan: run the test. Also verify the new test hit deadlock without the fix.
Reviewers: sdong, igor, lightmark
Reviewed By: lightmark
Subscribers: andrewkr, omegaga, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D60969
* Replace %zu format specifier with Windows-compatible macro 'ROCKSDB_PRIszt'
* Added "port/port.h" include to sim_cache.cc for call to snprintf().
* Applied cleaner fix to windows build, reverting part of 7bedd94
Summary: In T8216281 we decided to disable prefetching the index and filter during opening table handlers during startup (max_open_files = -1).
Test Plan: Rely on `IndexAndFilterBlocksOfNewTableAddedToCache` to guarantee L0 indexes and filters are still cached and change `PinL0IndexAndFilterBlocksTest` to make sure other levels are not cached (maybe add one more test to test we don't cache other levels?)
Reviewers: sdong, andrewkr
Reviewed By: andrewkr
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D59913
Summary: In many use cases there is no deletes. No need to pay the overhead of atomically updating num_deletes.
Test Plan: Run existing test.
Reviewers: ngbronson, yiwu, andrewkr, igor
Reviewed By: andrewkr
Subscribers: leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D60555
Summary:
Summary
There is a possibility that there is no L0 file after writing the data. Generate an L0 file to make it work.
Test Plan: Run the test many times.
Reviewers: andrewkr, yiwu
Reviewed By: yiwu
Subscribers: leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D60825
* Added new statistics and refactored to allow ioptions to be passed around as required to access environment and statistics pointers (and, as a convenient side effect, info_log pointer).
* Prevent incrementing compression counter when compression is turned off in options.
* Prevent incrementing compression counter when compression is turned off in options.
* Added two more supported compression types to test code in db_test.cc
* Prevent incrementing compression counter when compression is turned off in options.
* Added new StatsLevel that excludes compression timing.
* Fixed casting error in coding.h
* Fixed CompressionStatsTest for new StatsLevel.
* Removed unused variable that was breaking the Linux build
Summary: Each SST's file size increases after we add more table properties. Threshold in DBTest.DynamicLevelCompressionPerLevel need to adjust accordingly to avoid occasional failures.
Test Plan: Run the test
Reviewers: andrewkr, yiwu
Subscribers: leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D60819
Summary: If options.write_buffer_size is not set, nor options.write_buffer_manager, no need to update the bytes allocated counter in MemTableAllocator, which is expensive in parallel memtable insert case. Remove it can improve parallel memtable insert throughput by 10% with write batch size 128.
Test Plan:
Run benchmarks
TEST_TMPDIR=/dev/shm/ ./db_bench --benchmarks=fillrandom -disable_auto_compactions -level0_slowdown_writes_trigger=9999 -level0_stop_writes_trigger=9999 -num=10000000 --writes=1000000 -max_background_flushes=16 -max_write_buffer_number=16 --threads=32 --batch_size=128 -allow_concurrent_memtable_write -enable_write_thread_adaptive_yield
The throughput grows 10% with the benchmark.
Reviewers: andrewkr, yiwu, IslamAbdelRahman, igor, ngbronson
Reviewed By: ngbronson
Subscribers: ngbronson, leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D60465
Summary:
add DestroyColumnFamilyHandle(ColumnFamilyHandle**) to close column family instead of deleting cfh*
User should call this to close a cf and then we can detect the deletion in this function.
Test Plan: make all check -j64
Reviewers: andrewkr, yiwu, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D60765
Summary:
When write stalls because of auto compaction is disabled, or stop write trigger is reached,
user may change these two options to unblock writes. Unfortunately we had issue where the write
thread will block the attempt to persist the options, thus creating a deadlock. This diff
fix the issue and add two test cases to detect such deadlock.
Test Plan:
Run unit tests.
Also, revert db_impl.cc to master (but don't revert `DBImpl::BackgroundCompaction:Finish` sync point) and run db_options_test. Both tests should hit deadlock.
Reviewers: sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D60627
Summary:
I was investigating performance issues in the SstFileWriter and found all of the following:
- The SstFileWriter::Add() function created a local InternalKey every time it was called generating a allocation and free each time. Changed to have an InternalKey member variable that can be reset with the new InternalKey::Set() function.
- In SstFileWriter::Add() the smallest_key and largest_key values were assigned the result of a ToString() call, but it is simpler to just assign them directly from the user's key.
- The Slice class had no move constructor so each time one was returned from a function a new one had to be allocated, the old data copied to the new, and the old one was freed. I added the move constructor which also required a copy constructor and assignment operator.
- The BlockBuilder::CurrentSizeEstimate() function calculates the current estimate size, but was being called 2 or 3 times for each key added. I changed the class to maintain a running estimate (equal to the original calculation) so that the function can return an already calculated value.
- The code in BlockBuilder::Add() that calculated the shared bytes between the last key and the new key duplicated what Slice::difference_offset does, so I replaced it with the standard function.
- BlockBuilder::Add() had code to copy just the changed portion into the last key value (and asserted that it now matched the new key). It is more efficient just to copy the whole new key over.
- Moved this same code up into the 'if (use_delta_encoding_)' since the last key value is only needed when delta encoding is on.
- FlushBlockBySizePolicy::BlockAlmostFull calculated a standard deviation value each time it was called, but this information would only change if block_size of block_size_deviation changed, so I created a member variable to hold the value to avoid the calculation each time.
- Each PutVarint??() function has a buffer and calls std::string::append(). Two or three calls in a row could share a buffer and a single call to std::string::append().
Some of these will be helpful outside of the SstFileWriter. I'm not 100% the addition of the move constructor is appropriate as I wonder why this wasn't done before - maybe because of compiler compatibility? I tried it on gcc 4.8 and 4.9.
Test Plan: The changes should not affect the results so the existing tests should all still work and no new tests were added. The value of the changes was seen by manually testing the SstFileWriter class through MyRocks and adding timing code to identify problem areas.
Reviewers: sdong, IslamAbdelRahman
Reviewed By: IslamAbdelRahman
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D59607
Summary: fix Rocksdb Unit Test USER_FAILURE
Test Plan: make all check -j64
Reviewers: sdong, andrewkr
Reviewed By: andrewkr
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D60603
Summary:
DB::AddFile(std::string file_path) API that allow them to ingest an SST file created using SstFileWriter
We want to update this interface to be able to accept a list of files that will be ingested, DB::AddFile(std::vector<std::string> file_path_list).
Test Plan:
Add test case `AddExternalSstFileList` in `DBSSTTest`. To make sure:
1. files key ranges are not overlapping with each other
2. each file key range dont overlap with the DB key range
3. make sure no snapshots are held
Reviewers: andrewkr, sdong, IslamAbdelRahman
Reviewed By: IslamAbdelRahman
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D58587
