Summary:
Current Message
```
sst_dump [--command=check|scan|none|raw] [--verify_checksum] --file=data_dir_OR_sst_file [--output_hex] [--input_key_hex] [--from=<user_key>] [--to=<user_key>] [--read_num=NUM] [--show_properties] [--show_compression_sizes] [--show_compression_sizes [--set_block_size=<block_size>]]
```
New message
```
sst_dump --file=<data_dir_OR_sst_file> [--command=check|scan|raw]
--file=<data_dir_OR_sst_file>
Path to SST file or directory containing SST files
--command=check|scan|raw
check: Iterate over entries in files but dont print anything except if an error is encounterd (default command)
scan: Iterate over entries in files and print them to screen
raw: Dump all the table contents to <file_name>_dump.txt
--output_hex
Can be combined with scan command to print the keys and values in Hex
--from=<user_key>
Key to start reading from when executing check|scan
--to=<user_key>
Key to stop reading at when executing check|scan
--read_num=<num>
Maximum number of entries to read when executing check|scan
--verify_checksum
Verify file checksum when executing check|scan
--input_key_hex
Can be combined with --from and --to to indicate that these values are encoded in Hex
--show_properties
Print table properties after iterating over the file
--show_compression_sizes
Independent command that will recreate the SST file using 16K block size with different
compressions and report the size of the file using such compression
--set_block_size=<block_size>
Can be combined with --show_compression_sizes to set the block size that will be used
when trying different compression algorithms
```
Test Plan: none
Reviewers: yhchiang, andrewkr, kradhakrishnan, yiwu, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D56325
Summary:
Added the column family name to the properties block. This property
is omitted only if the property is unavailable, such as when RepairDB()
writes SST files.
In a next diff, I will change RepairDB to use this new property for
deciding to which column family an existing SST file belongs. If this
property is missing, it will add it to the "unknown" column family (same
as its existing behavior).
Test Plan:
New unit test:
$ ./db_table_properties_test --gtest_filter=DBTablePropertiesTest.GetColumnFamilyNameProperty
Reviewers: IslamAbdelRahman, yhchiang, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D55605
Summary:
Adapted a stderr logger from the option tests. Moved it to a separate
header so we can reuse it, e.g., from ldb subcommands for faster debugging. This
is especially useful to make errors/warnings more visible when running
"ldb repair", which involves potential data loss.
Test Plan:
ran options_test and "ldb repair"
$ ./ldb repair --db=./tmp/
[WARN] **** Repaired rocksdb ./tmp/; recovered 1 files; 588bytes. Some data may have been lost. ****
OK
Reviewers: IslamAbdelRahman, yhchiang, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D56151
Summary:
When a block based table file is opened, if prefetch_index_and_filter is true, it will prefetch the index and filter blocks, putting them into the block cache.
What this feature adds: when a L0 block based table file is opened, if pin_l0_filter_and_index_blocks_in_cache is true in the options (and prefetch_index_and_filter is true), then the filter and index blocks aren't released back to the block cache at the end of BlockBasedTableReader::Open(). Instead the table reader takes ownership of them, hence pinning them, ie. the LRU cache will never push them out. Meanwhile in the table reader, further accesses will not hit the block cache, thus avoiding lock contention.
Test Plan:
'export TEST_TMPDIR=/dev/shm/ && DISABLE_JEMALLOC=1 OPT=-g make all valgrind_check -j32' is OK.
I didn't run the Java tests, I don't have Java set up on my devserver.
Reviewers: sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D56133
Summary:
Undefined Behavior Sanitizer (ubsan) is //a good thing// which will help us to find sneaky bugs with low cost. Please see http://developerblog.redhat.com/2014/10/16/gcc-undefined-behavior-sanitizer-ubsan/ for more details and official GCC documentation for more context: https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html.
Changes itself are quite simple and pretty much imitating whatever is implemented for ASan.
Hooking the UBsan validation build to Sandcastle is a separate step and will be dealt as separate diff because code is in internal repository.
Test Plan: Make sure that that there no regressions when it comes to builds and test pass rate.
Reviewers: leveldb, sdong, IslamAbdelRahman, yhchiang
Reviewed By: yhchiang
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D56049
Summary:
Expose the inverse of ToString(hex=true) on Slice: Slice::DecodeHex
Refactor the other implementation of to/from hex in ldb_cmd.h to use the Slice
version
(Difference between the 2 is whether 0x is expected/produced in front of the hex
string or not)
Eliminated support for invalid odd length hex string - this is now invalid
instead of having 1/2 byte set
Added (inverse of HexToString) test for LDBCommand::StringToHex which also
indirectly tests Slice::ToString(true)
After moving the original implementation from ldb_cmd.h, updated it to much simpler/efficient version
(originally/inspired from https://github.com/facebook/wdt/blob/master/util/EncryptionUtils.cpp#L140-L169 )
Test Plan: run tests
Reviewers: uddipta, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D56121
record.size() should not be less than 12.
This "magic number" seems to be the WriteBatch header (8 byte sequence
and 4 byte count). Replaced all the places where "12" was used
by WriteBatchInternal::kHeader.
Summary: Test seems to fail if we don't use consistent version between testing forward and backward compatibility.
Test Plan: Run the script (with some version removed manually to make it shorter)
Reviewers: IslamAbdelRahman
Reviewed By: IslamAbdelRahman
Subscribers: leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D55773
Summary: After introducing a less forward-compatible change, update the backward compatible checking tool.
Test Plan: Run it.
Reviewers: IslamAbdelRahman
Reviewed By: IslamAbdelRahman
Subscribers: IslamAbdelRahman, leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D55695
Summary:
When a block based table file is opened, if prefetch_index_and_filter is true, it will prefetch the index and filter blocks, putting them into the block cache.
What this feature adds: when a L0 block based table file is opened, if pin_l0_filter_and_index_blocks_in_cache is true in the options (and prefetch_index_and_filter is true), then the filter and index blocks aren't released back to the block cache at the end of BlockBasedTableReader::Open(). Instead the table reader takes ownership of them, hence pinning them, ie. the LRU cache will never push them out. Meanwhile in the table reader, further accesses will not hit the block cache, thus avoiding lock contention.
When the table reader is destroyed, it releases the pinned blocks (if there were any). This has to happen before the cache is destroyed, so I had to introduce a TableReader::Close(), to guarantee the order of destruction.
Test Plan:
Added two unit tests for this. Existing unit tests run fine (default is pin_l0_filter_and_index_blocks_in_cache=false).
DISABLE_JEMALLOC=1 OPT=-g make all valgrind_check -j32
Mac: OK.
Linux: with D55287 patched in it's OK.
Reviewers: sdong
Reviewed By: sdong
Subscribers: andrewkr, leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D54801
Summary: For compactions benchmarks (both level and universal) we'll use `--max_write_buffer_number=4`. For all the other benchmarks which don't customize the value of `--max_background_flushes` we'll continue using `--max_write_buffer_number=8`.
Test Plan:
To validate basic correctness and command-line options:
```
cd ~/rocksdb
NKEYS=10000000 ./tools/run_flash_bench.sh
```
Reviewers: MarkCallaghan
Reviewed By: MarkCallaghan
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D55497
Summary: Set of updates to the subcompaction benchmark script which are based on our internal discussions. The intent behind the changes is to make sure that the scripts will correctly reflect how we're doing the actual benchmarking.
Test Plan: Tested by exercising the full set of compaction benchmarks and validating the execution and consistency of results.
Reviewers: MarkCallaghan, sdong, yhchiang
Reviewed By: yhchiang
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D55461
Summary: This will make it easier for admins and devs to use RepairDB.
Test Plan:
Tried deleting the manifest and verified it recovers:
$ ldb --create_if_missing --db=/tmp/test_db put ok ok
$ rm -f /tmp/test_db/MANIFEST-000001
$ ./ldb --db=/tmp/test_db repair
$ ldb --db=/tmp/test_db get ok
ok
Reviewers: yhchiang, sdong, IslamAbdelRahman
Reviewed By: IslamAbdelRahman
Subscribers: leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D55359
Summary: Refactored db_bench transaction stress tests so that they can be called from unit tests as well.
Test Plan: run new unit test as well as db_bench
Reviewers: yhchiang, IslamAbdelRahman, sdong
Reviewed By: IslamAbdelRahman
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D55203
Summary: After closely working with Mark, Siying, and Yueh-Hsuan this set of changes reflects the updates needed to measure RocksDB subcompaction performance in a correct manner. The essence of the benchmark is executing `fillrandom` followed by `compact` with the correct set of options for various number of subcompactions specified.
Test Plan: Tested internally to verify correctness and reliability.
Reviewers: sdong, yhchiang, MarkCallaghan
Reviewed By: MarkCallaghan
Subscribers: dhruba
Differential Revision: https://reviews.facebook.net/D55089
Test Plan:
Built and ran with gflags:
% ./db_bench
LevelDB: version 4.5
Date: Tue Feb 16 12:04:23 2016
CPU: 40 * Intel(R) Xeon(R) CPU E5-2660 v2 @ 2.20GHz
...
And without gflags:
% ./db_bench
Please install gflags to run rocksdb tools
%
Reviewers: sdong, igor
Reviewed By: igor
Subscribers: igor, dhruba
Differential Revision: https://reviews.facebook.net/D54243
Summary:
Implement a benchmark for universal compaction based on the feature description (see below), in-person discussions, and reading source code:
https://github.com/facebook/rocksdb/wiki/RocksDB-Tuning-Guidehttps://github.com/facebook/rocksdb/wiki/Universal-Compactionhttps://github.com/facebook/rocksdb/wiki/RocksDB-Tuning-Guide#universal-compaction
Universal compaction benchmark is based on `overwrite` benchmark, adding compaction specific options to it, and executing it for different values of subcompaction to understand the impact of scaling out subcompactions for a particular scenario.
Test Plan:
- Execute the benchmark on various machines for multiple iterations to verify the reliability.
- Observe the output to make sure that compaction is taking place.
- Observe the execution to make sure that arguments passed to `db_bench` are correct.
Reviewers: sdong, MarkCallaghan
Reviewed By: MarkCallaghan
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D54045
Summary: Default crash test uses prefix hash memtable, which is not compatible to concurrent memtable. Allow prefix test run with skip list and use skip list memtable when concurrent insert is used.
Test Plan: Run "python -u tools/db_crashtest.py whitebox" and watch sometimes skip list is used.
Reviewers: anthony, yhchiang, kradhakrishnan, andrewkr, IslamAbdelRahman
Reviewed By: IslamAbdelRahman
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D53907
Summary: If users turn on concurrent insert but the memtable doesn't support it, they might see unexcepted crash. Fix it by explicitly fail.
Test Plan:
Run different setting of stress_test and make sure it fails correctly.
Will add a unit test too.
Reviewers: anthony, kradhakrishnan, IslamAbdelRahman, yhchiang, andrewkr, ngbronson
Reviewed By: ngbronson
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D53895
Summary: This set of changes is part of the work to introduce benchmark for universal style compaction in RocksDB. It's conceptually separate from the compaction work, so sending it out as a separate diff to get it out of the way.
Test Plan:
- Run `./tools/run_flash_bench.sh`.
- Look at the contents of `report.txt` and `report2.txt` to make sure that data is reported and attributed correctly.
- During `db_bench` execution time make sure that the correct flags are passed to `--disable_wal` depending on the benchmark being executed.
Reviewers: MarkCallaghan
Reviewed By: MarkCallaghan
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D53865
Summary: Add an option of --allow_concurrent_memtable_write in stress test and cover it in crash test
Test Plan: Run crash test and make sure three combinations of the two options show up randomly.
Reviewers: IslamAbdelRahman, yhchiang, andrewkr, anthony, kradhakrishnan
Reviewed By: kradhakrishnan
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D53811
Summary:
Some of the tests aren't considered to be critical when it comes to getting key benchmarking data for RocksDB. Therefore we'll introduce an environment variable `SKIP_LOW_PRI_TESTS` which enables skipping those test cases. By default all the tests will be run. If you want to optimize the test-case execution then do the following:
`
$ export SKIP_LOW_PRI_TESTS=1
$ ./tools/run_flash_bench.sh
`
Test Plan: Verified that when `SKIP_LOW_PRI_TESTS` is not set then `benchmark.sh` is called for all the scenarios and when `SKIP_LOW_PRI_TESTS` is set to `1` then `benchmark.sh` is called only for the test-cases which are critical.
Reviewers: MarkCallaghan
Reviewed By: MarkCallaghan
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D53739
Summary:
Add an option --column_family option, so that users can query or update specific column family.
Also add an create column family parameter to make unit test easier.
Still need to add unit tests.
Test Plan: Will add a test case in ldb python test.
Reviewers: yhchiang, rven, andrewkr, IslamAbdelRahman, kradhakrishnan, anthony
Reviewed By: anthony
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D53265
Summary:
In crash test, when coming to each kill point, we start a random class using seed as current second. With this approach, for every second, the random number used is the same. However, in each second, there are multiple kill points with different frequency. It makes it hard to reason about chance of kill point to trigger. With this commit, we use thread local random seed to generate the random number, so that it will take different values per second, hoping it makes chances of killing much easier to reason about.
Also significantly reduce the kill odd to make sure time before kiling is similar as before.
Test Plan: Run white box crash test and see the killing happens as expected and the run time time before killing reasonable.
Reviewers: kradhakrishnan, IslamAbdelRahman, rven, yhchiang, andrewkr, anthony
Reviewed By: anthony
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D52971
Summary:
util/testutil.h doesn't seem to be used in tools/sst_dump_tool_imp.h. Remove it.
Also move some other include to tools/sst_dump_tool.cc instead.
Test Plan: Build with GCC, CLANG and with GCC 4.81 and 4.9.
Reviewers: yuslepukhin, yhchiang, rven, anthony, IslamAbdelRahman
Reviewed By: IslamAbdelRahman
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D52791
Summary:
This set of changes implements the following design: `ldb` will utilize `--path` parameter which can be used to specify a file name. Tool will then apply some heuristic to determine how to output the data properly. The design decision is not to probe the file content, but use file names to determine what dumping function to call.
Usage examples:
Understands that path points to a manifest file and dumps it.
`./ldb --path=/tmp/test_db/MANIFEST-000023 dump`
Understands that path points to a WAL file and dumps it.
`./ldb --path=/tmp/test_db/000024.log dump --header`
Understands that path points to a SST file and dumps it.
`./ldb --path=/tmp/test_db/000007.sst dump`
Figures out that none of the supported file types are applicable and outputs
an appropriate error message.
`./ldb --path=/tmp/cron.log dump`
Test Plan:
Basics:
git diff
make clean
make -j 32 commit-prereq
arc lint
More specific testing (done as part of commit-prereq, but can be iterated separately when making isolated changes):
make clean
make ldb
python tools/ldb_test.py
make rocksdb_dump
make rocksdb_undump
sh tools/rocksdb_dump_test.sh
Reviewers: rven, IslamAbdelRahman, yhchiang, kradhakrishnan, anthony, igor, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D52269
Summary:
1) changes tools/{benchmark,run_flash_bench}.sh to optionally use the write rate limit
2) removes code for --writes_per_second and switches the 'background' write rate limit
to use --benchmark_write_rate_limit
Replaces https://reviews.facebook.net/D49113
Task ID: #9555881
Blame Rev:
Test Plan:
tools/run_flash_bench.sh
Revert Plan:
Database Impact:
Memcache Impact:
Other Notes:
EImportant:
- begin *PUBLIC* platform impact section -
Bugzilla: #
- end platform impact -
Reviewers: igor
Reviewed By: igor
Subscribers: dhruba
Differential Revision: https://reviews.facebook.net/D52485
Summary:
When Get() or NewIterator() trigger file loads, skip caching the filter block if
(1) optimize_filters_for_hits is set and (2) the file is on the bottommost
level. Also skip checking filters under the same conditions, which means that
for a preloaded file or a file that was trivially-moved to the bottom level, its
filter block will eventually expire from the cache.
- added parameters/instance variables in various places in order to propagate the config ("skip_filters") from version_set to block_based_table_reader
- in BlockBasedTable::Rep, this optimization prevents filter from being loaded when the file is opened simply by setting filter_policy = nullptr
- in BlockBasedTable::Get/BlockBasedTable::NewIterator, this optimization prevents filter from being used (even if it was loaded already) by setting filter = nullptr
Test Plan:
updated unit test:
$ ./db_test --gtest_filter=DBTest.OptimizeFiltersForHits
will also run 'make check'
Reviewers: sdong, igor, paultuckfield, anthony, rven, kradhakrishnan, IslamAbdelRahman, yhchiang
Reviewed By: yhchiang
Subscribers: leveldb
Differential Revision: https://reviews.facebook.net/D51633
Summary:
Based on https://github.com/facebook/rocksdb/issues/843
It looks that when the data is hot we spend significant amount of time moving data out of RocksDB blocks. This patch reduce moving memory when possible
Original performance
```
$ time ./ldb --db=/home/tec/local/ellina_test/testdb scan > /dev/null
real 0m16.736s
user 0m11.993s
sys 0m4.725s
```
Performance after reducing memcpy
```
$ time ./ldb --db=/home/tec/local/ellina_test/testdb scan > /dev/null
real 0m11.590s
user 0m6.983s
sys 0m4.595s
```
Test Plan:
dump the output of the scan into 2 files and verifying the are exactly the same
make check
Reviewers: sdong, yhchiang, anthony, rven, igor
Reviewed By: igor
Subscribers: dhruba
Differential Revision: https://reviews.facebook.net/D51093
Summary: Now "ldb compact" skips the bottommost level compaction. This is an unintended behavior change. Reverting it now. Maybe we need to add another mode later for it.
Test Plan: Run a manual test of 'ldb' to make sure bottom most level is compacted.
Reviewers: IslamAbdelRahman, yhchiang, anthony, kradhakrishnan, rven
Reviewed By: rven
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D50925
Summary: We don't have access to GetLiveFilesMetadata() in RocksDB lite. If compiling write_stress for lite, I skip the check for leaked files, which depends on this function.
Test Plan: OPT=-DROCKSDB_LITE m write_stress
Reviewers: sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D49647
Summary:
The goal of this diff is to create a simple stress test with focus on catching:
* bugs in compaction/flush processes, especially the ones that cause assertion errors
* bugs in the code that deletes obsolete files
There are two parts of the test:
* write_stress, a binary that writes to the database
* write_stress_runner.py, a script that invokes and kills write_stress
Here are some interesting parts of write_stress:
* Runs with very high concurrency of compactions and flushes (32 threads total) and tries to create a huge amount of small files
* The keys written to the database are not uniformly distributed -- there is a 3-character prefix that mutates occasionally (in prefix mutator thread), in such a way that the first character mutates slower than second, which mutates slower than third character. That way, the compaction stress tests some interesting compaction features like trivial moves and bottommost level calculation
* There is a thread that creates an iterator, holds it for couple of seconds and then iterates over all keys. This is supposed to test RocksDB's abilities to keep the files alive when there are references to them.
* Some writes trigger WAL sync. This is stress testing our WAL sync code.
* At the end of the run, we make sure that we didn't leak any of the sst files
write_stress_runner.py changes the mode in which we run write_stress and also kills and restarts it. There are some interesting characteristics:
* At the beginning we divide the full test runtime into smaller parts -- shorter runtimes (couple of seconds) and longer runtimes (100, 1000) seconds
* The first time we run write_stress, we destroy the old DB. Every next time during the test, we use the same DB.
* We can run in kill mode or clean-restart mode. Kill mode kills the write_stress violently.
* We can run in mode where delete_obsolete_files_with_fullscan is true or false
* We can run with low_open_files mode turned on or off. When it's turned on, we configure table cache to only hold a couple of files -- that way we need to reopen files every time we access them.
Another goal was to create a stress test without a lot of parameters. So tools/write_stress_runner.py should only take one parameter -- runtime_sec and it should figure out everything else on its own.
In a separate diff, I'll add this new test to our nightly legocastle runs.
Test Plan:
The goal of this test was to retroactively catch the following bugs: D33045, D48201, D46899, D42399. I failed to reproduce D48201, but all others have been caught!
When i reverted https://reviews.facebook.net/D33045:
./write_stress --runtime_sec=200 --low_open_files_mode=true
Iterator statuts not OK: IO error: /fast-rocksdb-tmp/rocksdb_test/write_stress/089166.sst: No such file or directory
When i reverted https://reviews.facebook.net/D42399:
python tools/write_stress_runner.py --runtime_sec=5000
Running write_stress, will kill after 5 seconds: ./write_stress --runtime_sec=-1
Running write_stress, will kill after 2 seconds: ./write_stress --runtime_sec=-1 --destroy_db=false --delete_obsolete_files_with_fullscan=true
Running write_stress, will kill after 7 seconds: ./write_stress --runtime_sec=-1 --destroy_db=false
Running write_stress, will kill after 5 seconds: ./write_stress --runtime_sec=-1 --destroy_db=false
Running write_stress, will kill after 8 seconds: ./write_stress --runtime_sec=-1 --destroy_db=false --low_open_files_mode=true
Write to DB failed: IO error: /fast-rocksdb-tmp/rocksdb_test/write_stress/019250.sst: No such file or directory
ERROR: write_stress died with exitcode=-6
When i reverted https://reviews.facebook.net/D46899:
python tools/write_stress_runner.py --runtime_sec=1000
runtime: 1000
Going to execute write stress for [3, 3, 100, 3, 2, 100, 1, 788]
Running write_stress for 3 seconds: ./write_stress --runtime_sec=3 --low_open_files_mode=true
Running write_stress for 3 seconds: ./write_stress --runtime_sec=3 --destroy_db=false --delete_obsolete_files_with_fullscan=true
Running write_stress, will kill after 100 seconds: ./write_stress --runtime_sec=-1 --destroy_db=false --delete_obsolete_files_with_fullscan=true
write_stress: db/db_impl.cc:2070: void rocksdb::DBImpl::MarkLogsSynced(uint64_t, bool, const rocksdb::Status&): Assertion `log.getting_synced' failed.
ERROR: write_stress died with exitcode=-6
Reviewers: IslamAbdelRahman, yhchiang, rven, kradhakrishnan, sdong, anthony
Reviewed By: anthony
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D49533
Summary: crash_test still has a very low chance to hit some crash point. Have another mode for covering them more likely.
Test Plan: Run crash_test and see db_stress is called with expected prameters.
Reviewers: kradhakrishnan, igor, anthony, rven, IslamAbdelRahman, yhchiang
Reviewed By: yhchiang
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D49473
