Summary:
Compaction now boosts the size of deletion entries of a file only when
the number of deletion entries is greater than the number of non-deletion
entries in the file. The motivation here is that in a stable workload,
the number of deletion entries should be roughly equal to the number of
non-deletion entries. If we compensate the size of deletion entries in a
stable workload, the deletion compensation logic might introduce unwanted
effet which changes the shape of LSM tree.
Test Plan: db_test --gtest_filter="*Deletion*"
Reviewers: sdong, igor
Reviewed By: igor
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D38703
Summary:
This turns out to be pretty bad because if we prioritize L0->L1 then L1 can grow artificially large, which makes L0->L1 more and more expensive. For example:
256MB @ L0 + 256MB @ L1 --> 512MB @ L1
256MB @ L0 + 512MB @ L1 --> 768MB @ L1
256MB @ L0 + 768MB @ L1 --> 1GB @ L1
....
256MB @ L0 + 10GB @ L1 --> 10.2GB @ L1
At some point we need to start compacting L1->L2 to speed up L0->L1.
Test Plan:
The performance improvement is massive for heavy write workload. This is the benchmark I ran: https://phabricator.fb.com/P19842671. Before this change, the benchmark took 47 minutes to complete. After, the benchmark finished in 2minutes. You can see full results here: https://phabricator.fb.com/P19842674
Also, we ran this diff on MongoDB on RocksDB on one replicaset. Before the change, our initial sync was so slow that it couldn't keep up with primary writes. After the change, the import finished without any issues
Reviewers: dynamike, MarkCallaghan, rven, yhchiang, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D38637
Summary:
CPU profiling reveals GetApproximateSizes as a bottleneck for performance. The current implementation is sub-optimal, it scans every file in every level to compute the result.
We can take advantage of the fact that all levels above 0 are sorted in the increasing order of key ranges and use binary search to locate the starting index. This can reduce the number of comparisons required to compute the result.
Test Plan: We have good test coverage. Run the tests.
Reviewers: sdong, igor, rven, dynamike
Subscribers: dynamike, maykov, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D37755
Summary:
Based on feedback from D37083.
Are all of these correct? In some spaces it seems like we're doing SetMaxPossibleForUserKey() although we want the smallest possible internal key for user key.
Test Plan: make check
Reviewers: sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D37341
Summary: Add more logging to help debugging issues.
Test Plan: Run test suites
Reviewers: yhchiang, rven, igor
Reviewed By: igor
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D37401
Summary:
Some Mongo+Rocks datasets in Parse's environment are not doing compactions very frequently. During the quiet period (with no IO), we'd like to schedule compactions so that our reads become faster. Also, aggressively compacting during quiet periods helps when write bursts happen. In addition, we also want to compact files that are containing deleted key ranges (like old oplog keys).
All of this is currently not possible with CompactRange() because it's single-threaded and blocks all other compactions from happening. Running CompactRange() risks an issue of blocking writes because we generate too much Level 0 files before the compaction is over. Stopping writes is very dangerous because they hold transaction locks. We tried running manual compaction once on Mongo+Rocks and everything fell apart.
MarkForCompaction() solves all of those problems. This is very light-weight manual compaction. It is lower priority than automatic compactions, which means it shouldn't interfere with background process keeping the LSM tree clean. However, if no automatic compactions need to be run (or we have extra background threads available), we will start compacting files that are marked for compaction.
Test Plan: added a new unit test
Reviewers: yhchiang, rven, MarkCallaghan, sdong
Reviewed By: sdong
Subscribers: yoshinorim, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D37083
Summary:
If accumulated_num_non_deletions_ were ever smaller than
accumulated_num_deletions_, the computation of
"accumulated_num_non_deletions_ - accumulated_num_deletions_"
would result in a logically "negative" value, but since
the two operands are unsigned (uint64_t), the result corresponding
to e.g., -1 would 2^64-1.
Instead, return 0 in that case.
Test Plan:
- ensure "make check" still passes
- temporarily add an "abort();" call in the new "if"-block, and
observe that it fails in some test cases. However, note that
this case is triggered only when the two numbers are equal.
Thus, no test case triggers the erroneous behavior this
change is designed to avoid. If anyone can construct a
scenario in which that bug would be triggered, I'll be
happy to add a test case.
Reviewers: ljin, igor, rven, igor.sugak, yhchiang, sdong
Reviewed By: sdong
Subscribers: dhruba
Differential Revision: https://reviews.facebook.net/D36489
Summary: Int is used for level size targets when options_.level_compaction_dynamic_level_bytes=true, which will cause overflow when database grows big. Fix it.
Test Plan: Add a new unit test which fails without the fix.
Reviewers: rven, yhchiang, MarkCallaghan, igor
Reviewed By: igor
Subscribers: leveldb, dhruba, yoshinorim
Differential Revision: https://reviews.facebook.net/D36453
Summary:
With this change, we use L1 and up to store compaction outputs in universal compaction.
The compaction pick logic stays the same. Outputs are stored in the largest "level" as possible.
If options.num_levels=1, it behaves all the same as now.
Test Plan:
1) convert most of existing unit tests for universal comapaction to include the option of one level and multiple levels.
2) add a unit test to cover parallel compaction in universal compaction and run it in one level and multiple levels
3) add unit test to migrate from multiple level setting back to one level setting
4) add a unit test to insert keys to trigger multiple rounds of compactions and verify results.
Reviewers: rven, kradhakrishnan, yhchiang, igor
Reviewed By: igor
Subscribers: meyering, leveldb, MarkCallaghan, dhruba
Differential Revision: https://reviews.facebook.net/D34539
Summary:
We have addded new stats and perf_context for measuring the merge and filter operation time consumption.
We have bounded all the merge operations within the GUARD statment and collected the total time for these operations in the DB.
Test Plan: WIP
Reviewers: rven, yhchiang, kradhakrishnan, igor, sdong
Reviewed By: sdong
Subscribers: dhruba
Differential Revision: https://reviews.facebook.net/D34377
Summary:
To understand the bug read t5943287 and check out the new test in column_family_test (ReadDroppedColumnFamily), iter 0.
RocksDB contract allowes you to read a drop column family as long as there is a live reference. However, since our iteration ignores dropped column families, AddLiveFiles() didn't mark files of a dropped column families as live. So we deleted them.
In this patch I no longer ignore dropped column families in the iteration. I think this behavior was confusing and it also led to this bug. Now if an iterator client wants to ignore dropped column families, he needs to do it explicitly.
Test Plan: Added a new unit test that is failing on master. Unit test succeeds now.
Reviewers: sdong, rven, yhchiang
Reviewed By: yhchiang
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D32535
Summary: It is no longer used by the implementation, so we should also remove it from the public API.
Test Plan: make check
Reviewers: sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D34971
Summary:
When having fixed max_bytes_for_level_base, the ratio of size of largest level and the second one can range from 0 to the multiplier. This makes LSM tree frequently irregular and unpredictable. It can also cause poor space amplification in some cases.
In this improvement (proposed by Igor Kabiljo), we introduce a parameter option.level_compaction_use_dynamic_max_bytes. When turning it on, RocksDB is free to pick a level base in the range of (options.max_bytes_for_level_base/options.max_bytes_for_level_multiplier, options.max_bytes_for_level_base] so that real level ratios are close to options.max_bytes_for_level_multiplier.
Test Plan: New unit tests and pass tests suites including valgrind.
Reviewers: MarkCallaghan, rven, yhchiang, igor, ikabiljo
Reviewed By: ikabiljo
Subscribers: yoshinorim, ikabiljo, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D31437
Summary:
When using latest clang (3.6 or 3.7/trunck) rocksdb is failing with many errors. Almost all of them are missing override errors. This diff adds missing override keyword. No manual changes.
Prerequisites: bear and clang 3.5 build with extra tools
```lang=bash
% USE_CLANG=1 bear make all # generate a compilation database http://clang.llvm.org/docs/JSONCompilationDatabase.html
% clang-modernize -p . -include . -add-override
% make format
```
Test Plan:
Make sure all tests are passing.
```lang=bash
% #Use default fb code clang.
% make check
```
Verify less error and no missing override errors.
```lang=bash
% # Have trunk clang present in path.
% ROCKSDB_NO_FBCODE=1 CC=clang CXX=clang++ make
```
Reviewers: igor, kradhakrishnan, rven, meyering, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D34077
Summary:
Remove some always-true assertions.
They provoke these compilation failures:
table/plain_table_key_coding.cc:279:20: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
db/version_set.cc:336:15: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
* table/plain_table_key_coding.cc (rocksdb): Remove assertion that
unsigned type variable is >= 0.
* db/version_set.cc (DoGenerateLevelFilesBrief): Likewise.
Test Plan:
Run "make EXTRA_CXXFLAGS='-W -Wextra'" and see fewer errors.
Reviewers: ljin, sdong, igor.sugak, igor
Reviewed By: igor
Subscribers: dhruba
Differential Revision: https://reviews.facebook.net/D33747
Summary: Add a DB property about live versions. It can be helpful to figure out whether there are files not live but not yet deleted, in some use cases.
Test Plan: make all check
Reviewers: rven, yhchiang, igor
Reviewed By: igor
Subscribers: yoshinorim, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D33327
Summary: For description of the bug, see comment in db_test. The fix is pretty straight forward.
Test Plan: added unit test. eventually we need better testing of FOF/POF process.
Reviewers: yhchiang, rven, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D33081
Summary:
- In statistics.h , added tickers.
- In version_set.cc,
-- Added a getter method for hit_file_level_ in the class FilePicker
-- Added a line in the Get() method in case of a found, increment the corresponding counters based on the level of the file respectively.
Corresponding task: https://our.intern.facebook.com/intern/tasks/?s=506100481&t=5952818
Personal fork: 0c3f2e3600
Test Plan:
In terminal,
```
make -j32 db_test
ROCKSDB_TESTS=L0L1L2AndUpHitCounter ./db_test
```
Or to use debugger,
```
make -j32 db_test
export ROCKSDB_TESTS=L0L1L2AndUpHitCounter
gdb db_test
```
Reviewers: rven, sdong
Reviewed By: sdong
Subscribers: dhruba
Differential Revision: https://reviews.facebook.net/D32205
Summary:
This diff basically reverts D30249 and also adds a unit test that was failing before this patch.
I have no idea how I didn't catch this terrible bug when writing a diff, sorry about that :(
I think we should redesign our system of keeping track of and deleting files. This is already a second bug in this critical piece of code. I'll think of few ideas.
BTW this diff is also a regression when running lots of column families. I plan to revisit this separately.
Test Plan: added a unit test
Reviewers: yhchiang, rven, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D33045
Summary:
Add a counter for collecting the wait time on db mutex.
Also add MutexWrapper and CondVarWrapper for measuring wait time.
Test Plan:
./db_test
export ROCKSDB_TESTS=MutexWaitStats
./db_test
verify stats output using db_bench
make clean
make release
./db_bench --statistics=1 --benchmarks=fillseq,readwhilewriting --num=10000 --threads=10
Sample output:
rocksdb.db.mutex.wait.micros COUNT : 7546866
Reviewers: MarkCallaghan, rven, sdong, igor
Reviewed By: igor
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D32787
Summary: Added requirement that ComputeCompactionScore() be executed in mutex, since it's accessing being_compacted bool, which can be mutated by other threads. Also added more comments about thread safety of FileMetaData, since it was a bit confusing. However, it seems that FileMetaData doesn't have data races (except being_compacted)
Test Plan: Ran 100 ConvertCompactionStyle tests with thread sanitizer. On master -- some failures. With this patch -- none.
Reviewers: yhchiang, rven, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D32283
Summary: Now we don't sync manifest file when initializing it, so DB cannot be safely reopened before the first mem table flush. Fix it by syncing it. This fixes fault_injection_test.
Test Plan: make all check
Reviewers: rven, yhchiang, igor
Reviewed By: igor
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D32001
Test Plan: Compile. Run it.
Reviewers: yhchiang, dhruba, igor
Reviewed By: igor
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D31479
Summary: Add an extra assert to make sure current version is included in VersionSet::AddLiveFiles().
Test Plan: make all check
Reviewers: yhchiang, rven, igor
Reviewed By: igor
Subscribers: dhruba, hermanlee4, leveldb
Differential Revision: https://reviews.facebook.net/D30819
Summary:
There are two versions of FindObsoleteFiles():
* full scan, which is executed every 6 hours (and it's terribly slow)
* no full scan, which is executed every time a background process finishes and iterator is deleted
This diff is optimizing the second case (no full scan). Here's what we do before the diff:
* Get the list of obsolete files (files with ref==0). Some files in obsolete_files set might actually be live.
* Get the list of live files to avoid deleting files that are live.
* Delete files that are in obsolete_files and not in live_files.
After this diff:
* The only files with ref==0 that are still live are files that have been part of move compaction. Don't include moved files in obsolete_files.
* Get the list of obsolete files (which exclude moved files).
* No need to get the list of live files, since all files in obsolete_files need to be deleted.
I'll post the benchmark results, but you can get the feel of it here: https://reviews.facebook.net/D30123
This depends on D30123.
P.S. We should do full scan only in failure scenarios, not every 6 hours. I'll do this in a follow-up diff.
Test Plan:
One new unit test. Made sure that unit test fails if we don't have a `if (!f->moved)` safeguard in ~Version.
make check
Big number of compactions and flushes:
./db_stress --threads=30 --ops_per_thread=20000000 --max_key=10000 --column_families=20 --clear_column_family_one_in=10000000 --verify_before_write=0 --reopen=15 --max_background_compactions=10 --max_background_flushes=10 --db=/fast-rocksdb-tmp/db_stress --prefixpercent=0 --iterpercent=0 --writepercent=75 --db_write_buffer_size=2000000
Reviewers: yhchiang, rven, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D30249
Summary:
Introduces a new class for managing write buffer memory across column
families. We supplement ColumnFamilyOptions::write_buffer_size with
ColumnFamilyOptions::write_buffer, a shared pointer to a WriteBuffer
instance that enforces memory limits before flushing out to disk.
Test Plan: Added SharedWriteBuffer unit test to db_test.cc
Reviewers: sdong, rven, ljin, igor
Reviewed By: igor
Subscribers: tnovak, yhchiang, dhruba, xjin, MarkCallaghan, yoshinorim
Differential Revision: https://reviews.facebook.net/D22581
Summary:
Reported by bootcamper
This causes ldb tool to fail the assertion in ~ColumnFamilyData()
Test Plan:
./ldb --db=/tmp/test_db1 --create_if_missing put a1 b1
./ldb manifest_dump --path=/tmp/test_db1/MANIFEST-000001
Reviewers: sdong, yhchiang, rven, igor
Reviewed By: igor
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D29517
Summary:
The very last reference happens in DBImpl::GetOptions()
I built with both DBImpl::GetOptions() and ColumnFamilyData::options() commented out
Test Plan: make all check
Reviewers: sdong, yhchiang, igor
Reviewed By: igor
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D29073
Summary:
Move NeedsCompaction() from VersionStorageInfo to CompactionPicker
to allow different compaction strategy to have their own way to
determine whether doing compaction is necessary.
When compaction style is set to kCompactionStyleNone, then
NeedsCompaction() will always return false.
Test Plan:
export ROCKSDB_TESTS=Compact
./db_test
Reviewers: ljin, sdong, igor
Reviewed By: igor
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D28719
Summary: So iOS size_t is 32-bit, so we need to static_cast<size_t> any uint64_t :(
Test Plan: TARGET_OS=IOS make static_lib
Reviewers: dhruba, ljin, yhchiang, rven, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D28743
Summary: I found that db_stress sometimes segfault on my machine. Fix the bug.
Test Plan: make all check. Run db_stress
Reviewers: ljin, yhchiang, rven, igor
Reviewed By: igor
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D28803
Summary:
Fixed a bug in GetEstimatedActiveKeys which does not normalized
the sampled information correctly.
Add a test in version_builder_test.
Test Plan: version_builder_test
Reviewers: ljin, igor, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D28707
Summary:
We need to turn on -Wshorten-64-to-32 for mobile. See D1671432 (internal phabricator) for details.
This diff turns on the warning flag and fixes all the errors. There were also some interesting errors that I might call bugs, especially in plain table. Going forward, I think it makes sense to have this flag turned on and be very very careful when converting 64-bit to 32-bit variables.
Test Plan: compiles
Reviewers: ljin, rven, yhchiang, sdong
Reviewed By: yhchiang
Subscribers: bobbaldwin, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D28689
Summary: Based on @sdong's feedback in the diff, we shouldn't keep db_mutex in CompactionJob's state. This diff removes db_mutex from CompactionJob state, by making next_file_number_ atomic. That way we only need to pass the lock to InstallCompactionResults() because of LogAndApply()
Test Plan: make check
Reviewers: ljin, yhchiang, rven, sdong
Reviewed By: sdong
Subscribers: sdong, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D28491
Summary:
This diff adds three sets of APIs to RocksDB.
= GetColumnFamilyMetaData =
* This APIs allow users to obtain the current state of a RocksDB instance on one column family.
* See GetColumnFamilyMetaData in include/rocksdb/db.h
= EventListener =
* A virtual class that allows users to implement a set of
call-back functions which will be called when specific
events of a RocksDB instance happens.
* To register EventListener, simply insert an EventListener to ColumnFamilyOptions::listeners
= CompactFiles =
* CompactFiles API inputs a set of file numbers and an output level, and RocksDB
will try to compact those files into the specified level.
= Example =
* Example code can be found in example/compact_files_example.cc, which implements
a simple external compactor using EventListener, GetColumnFamilyMetaData, and
CompactFiles API.
Test Plan:
listener_test
compactor_test
example/compact_files_example
export ROCKSDB_TESTS=CompactFiles
db_test
export ROCKSDB_TESTS=MetaData
db_test
Reviewers: ljin, igor, rven, sdong
Reviewed By: sdong
Subscribers: MarkCallaghan, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D24705
Summary: It turns out that -Wshadow has different rules for gcc than clang. Previous commit fixed clang. This commits fixes the rest of the warnings for gcc.
Test Plan: compiles
Reviewers: ljin, yhchiang, rven, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D28131
Summary: Apply InfoLogLevel to the logs in db/version_set.cc
Test Plan: make
Reviewers: ljin, sdong, igor
Reviewed By: igor
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D27879
Summary: Enforce the accessier naming convention in functions in version_set.h
Test Plan: make all check
Reviewers: ljin, yhchiang, rven, igor
Reviewed By: igor
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D28143
Summary: Move all the logic of VersionBuilder to a separate .cc file
Test Plan: make all check
Reviewers: ljin, yhchiang, rven, igor
Reviewed By: igor
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D28083
Summary: BaseReferencedVersionBuilder now unreference version before destructing VersionBuilder, which is wrong. Fix it.
Test Plan:
make all check
valgrind test to tests that used to fail
Reviewers: igor, yhchiang, rven, ljin
Reviewed By: ljin
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D28101
Summary:
...and fix all the errors :)
Jim suggested turning on -Wshadow because it helped him fix number of critical bugs in fbcode. I think it's a good idea to be -Wshadow clean.
Test Plan: compiles
Reviewers: yhchiang, rven, sdong, ljin
Reviewed By: ljin
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D27711
Summary:
Rename Version::Builder to VersionBuilder and expose its definition to a header.
Make VerisonBuilder not reference Version or ColumnFamilyData, only working with VersionStorageInfo.
Add version_builder_test which has a simple test.
Test Plan: make all check
Reviewers: rven, yhchiang, igor, ljin
Reviewed By: igor
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D27969
Summary:
Make compaction picker easier to test.
The basic idea is to separate a minimum subcomponent of Version to VersionStorageInfo, which just responsible to LSM tree. A stub VersionStorageInfo can then be easily created and passed into compaction picker so that we can check the outputs.
It now passes most tests. Still two things need to be done:
(1) deal with the FIFO compaction's file size.
(2) write an example test to make sure the interface can do the job.
Add a compaction_picker_test to make sure compaction picker codes can be easily unit tested.
Test Plan:
Pass all unit tests and compaction_picker_test
Reviewers: yhchiang, rven, igor, ljin
Reviewed By: ljin
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D27639
Summary:
This diff has two fixes.
1. Fix the bug where compaction does not fail when RocksDB can't create a new file.
2. When NewWritableFiles() fails in OpenCompactionOutputFiles(), previously such fail-to-created file will be still be included as a compaction output. This patch also fixes this bug.
3. Allow VersionEdit::EncodeTo() to return Status and add basic check.
Test Plan:
./version_edit_test
export ROCKSDB_TESTS=FileCreationRandomFailure
./db_test
Reviewers: ljin, sdong, nkg-, igor
Reviewed By: igor
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D25581
Summary: No need to expose them in .h
Test Plan: make release
Reviewers: igor, yhchiang, rven, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D27645
Summary: as title
Test Plan:
make release
will run full test on all stacked diffs before committing
Reviewers: sdong, yhchiang, rven, igor
Reviewed By: igor
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D27591
Summary:
We have several different types of data structures for file information.
FileLevel is kinda of confusing since it only contains file range and
fd. Rename it to LevelFilesBrief to make it clear.
Unfriend CompactedDBImpl as a by product
Test Plan:
make release / make all
will run full test with all stacked diffs
Reviewers: sdong, yhchiang, rven, igor
Reviewed By: igor
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D27585
