Commit Graph

1000 Commits

Author SHA1 Message Date
sdong dd337bc0b2 In logging format, use PRIu64 instead of casting
Summary: Code cleaning up, since we are already using __STDC_FORMAT_MACROS in printing uint64_t, change other places. Only logging is changed.

Test Plan: make all check

Reviewers: ljin

Reviewed By: ljin

Subscribers: dhruba, yhchiang, haobo, leveldb

Differential Revision: https://reviews.facebook.net/D19113
2014-06-27 16:34:15 -07:00
Stanislau Hlebik a3594867ba Cache some conditions for DBImpl::MakeRoomForWrite
Summary:
Task 4580155. Some conditions in DBImpl::MakeRoomForWrite can be cached in
ColumnFamilyData, because theirs value can be changed only during compaction,
adding new memtable and/or add recalculation of compaction score.

These conditions are:

cfd->imm()->size() ==  cfd->options()->max_write_buffer_number - 1
cfd->current()->NumLevelFiles(0) >=  cfd->options()->level0_stop_writes_trigger
cfd->options()->soft_rate_limit > 0.0 &&
    (score = cfd->current()->MaxCompactionScore()) >  cfd->options()->soft_rate_limit
cfd->options()->hard_rate_limit > 1.0 &&
    (score = cfd->current()->MaxCompactionScore()) >  cfd->options()->hard_rate_limit

P.S.
As it's my first diff, Siying suggested to add everybody as a reviewers
for this diff. Sorry, if I forgot someone or add someone by mistake.

Test Plan: make all check

Reviewers: haobo, xjin, dhruba, yhchiang, zagfox, ljin, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19311
2014-06-26 16:45:27 -07:00
sdong 19de6a7aad Remove MemTableRep::GetIterator(const Slice& slice)
Summary: It seems to me that when ever function MemTableRep::GetIterator(const Slice& slice) is used, we can use MemTableRep::GetDynamicPrefixIterator() instead. Just delete it to simplify the codes.

Test Plan: make all check

Reviewers: yhchiang, ljin

Reviewed By: ljin

Subscribers: xjin, dhruba, haobo, leveldb

Differential Revision: https://reviews.facebook.net/D19281
2014-06-25 14:09:29 -07:00
Yueh-Hsuan Chiang 8898a0a0d1 Reorder the member variables of FileMetaData to improve cache locality.
Summary:
Move stats related member variables of FileMetaData to the bottom to
improve cache locality of normal DB operations.

Test Plan: make

Reviewers: haobo, ljin, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19287
2014-06-24 19:22:11 -06:00
Yueh-Hsuan Chiang e813f5b6d9 Allow compaction to reclaim storage more effectively.
Summary:
This diff allows compaction to reclaim storage more effectively.
In the current design, compactions are mainly triggered based on
the file sizes.  However, since deletion entries does not have
value, files which have many deletion entries are less likely
to be compacted.  As a result, it may took a while to make
deletion entries to be compacted.

This diff address issue by compensating the size of deletion
entries during compaction process: the size of each deletion
entry in the compaction process is augmented by 2x average
value size.  The diff applies to both leveled and universal
compacitons.

Test Plan:
develop CompactionDeletionTrigger
make db_test
./db_test

Reviewers: haobo, igor, ljin, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19029
2014-06-24 16:37:06 -06:00
Yueh-Hsuan Chiang faa8d21922 Improve an assertion in RandomGenerator::Generate() in db_bench.
Summary:
RandomGenerator::Generate() currently has an assertion len < data_.size().
However, it is actually fine to have len == data_.size().
This diff change the assertion to len <= data_.size().

Test Plan:
make db_bench
./db_bench

Reviewers: haobo, sdong, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19269
2014-06-24 15:29:28 -06:00
Lei Jin 3b0dc76699 db_bench: measure the real latency of write/delete
Summary: as title

Test Plan: make release

Reviewers: haobo, sdong, yhchiang

Reviewed By: yhchiang

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19227
2014-06-23 13:23:02 -07:00
Lei Jin a1b5650a75 db_bench: sanity check on compression ratio
Summary: as requested by mark

Test Plan: make release

Reviewers: sdong, haobo

Reviewed By: haobo

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19221
2014-06-23 10:46:16 -07:00
Igor Canadi d4a8423334 Remove seek compaction
Summary:
As discussed in our internal group, we don't get much use of seek compaction at the moment, while it's making code more complicated and slower in some cases.

This diff removes seek compaction and (hopefully) all code that was introduced to support seek compaction.

There is one test case that relied on didIO information. I'll try to find another way to implement it.

Test Plan: make check

Reviewers: sdong, haobo, yhchiang, ljin, dhruba

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19161
2014-06-20 10:23:02 +02:00
Igor Canadi 107e08baa7 Use same sorting for all level 0 files
Summary:
We decided that one of the long term goals is to unify level and universal compaction.

As a small first step, I'm unifying level 0 sorting methods.

Previously, we used to sort level 0 files in level compaction by file number and in universal compaction by sequence number.

But it turns out that in level compaction, sorting by file number is exactly the same as sorting by sequence number.

Test Plan:
Ran make check with bunch of asserts to verify the sorting order is exactly the same.
Also, make check with this patch

Reviewers: haobo, yhchiang, ljin, dhruba, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19131
2014-06-20 09:12:14 +02:00
Haobo Xu 7a9dd5f214 [RocksDB] Make block based table hash index more adaptive
Summary: Currently, RocksDB returns error if a db written with prefix hash index, is later opened without providing a prefix extractor. This is uncessarily harsh. Without a prefix extractor, we could always fallback to the normal binary index.

Test Plan: unit test, also manually veried LOG that fallback did occur.

Reviewers: sdong, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19191
2014-06-19 16:40:32 -07:00
Yueh-Hsuan Chiang 4f5ccfd179 Fixed a potential write hang
Summary:
Currently, when something badly happen in the DB::Write() while the write-queue
contains more than one element, the current design seems to forget to clean up
the queue as well as wake-up all the writers, this potentially makes rocksdb
hang on writes.

Test Plan: make all check

Reviewers: sdong, ljin, igor, haobo

Reviewed By: haobo

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19167
2014-06-19 14:53:03 -07:00
Igor Canadi bae495740d Merge pull request #179 from edsrzf/c-api-compaction-filter
Support for compaction filters in the C API
2014-06-19 21:22:46 +02:00
Lei Jin c4e90c79ed bug fix: iteration over ColumnFamilySet needs to be under mutex
Summary: asan_crash_test is failing on segfault

Test Plan: running asan_crash_test

Reviewers: sdong, igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19149
2014-06-19 09:31:14 -07:00
Evan Shaw 5363eb8ad4 Add a test for using compaction filters via the C API 2014-06-19 21:46:58 +12:00
Evan Shaw d72313a7fa Add a way to set compaction filter in the C API 2014-06-19 16:31:24 +12:00
Evan Shaw df2701373d Support for compaction filters in the C API 2014-06-19 16:31:17 +12:00
sdong edd47c5104 PlainTable to encode to avoid to rewrite prefix when it is the same as the previous key
Summary:
Add a encoding feature of PlainTable to encode PlainTable's keys to save some bytes for the same prefixes.
The data format is documented in table/plain_table_factory.h

Test Plan: Add unit test coverage in plain_table_db_test

Reviewers: yhchiang, igor, dhruba, ljin, haobo

Reviewed By: haobo

Subscribers: nkg-, leveldb

Differential Revision: https://reviews.facebook.net/D18735
2014-06-18 20:41:52 -07:00
Igor Canadi 3525aac9e5 Change order of parameters in adaptive table factory
Summary:
This is minor, but if we put the writing talbe factory as the third parameter, when we add a new table format, we'll have a situation:
1) block based factory
2) plain table factory
3) output factory
4) new format factory

I think it makes more sense to have output as the first parameter.

Also, fixed a NewAdaptiveTableFactory() call in unit test

Test Plan: unit test

Reviewers: sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19119
2014-06-18 07:04:37 +02:00
sdong 8c265c08f1 HashLinkList to log distribution of number of entries aross buckets
Summary: Add two parameters of hash linked list to log distribution of number of entries across all buckets, and a sample row when there are too many entries in one single bucket.

Test Plan: Turn it on in plain_table_db_test and see the logs.

Reviewers: haobo, ljin

Reviewed By: ljin

Subscribers: leveldb, nkg-, dhruba, yhchiang

Differential Revision: https://reviews.facebook.net/D19095
2014-06-17 17:55:36 -07:00
sdong 200e4b4a72 Add a table factory that can read DB with both of PlainTable and BlockBasedTable in it
Summary: The new table factory is used if users want to convert a DB from one table format to the other. A user can use this table to open a DB written using one table format and write new files to another table format.

Test Plan: add a unit test

Reviewers: haobo, igor

Reviewed By: igor

Subscribers: dhruba, ljin, yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D19017
2014-06-17 11:49:22 -07:00
Igor Canadi 4f18bfe376 Merge pull request #176 from bgrainger/mutexrw-unlock
Add separate Read/WriteUnlock methods in MutexRW.
2014-06-17 20:38:06 +02:00
Yueh-Hsuan Chiang e6e259b8ab Include max_write_buffer_number >= 2 to SanitizeOptions.
Summary: Include max_write_buffer_number >= 2 to SanitizeOptions.

Test Plan: make all check

Reviewers: haobo, sdong, igor, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19077
2014-06-16 16:26:46 -07:00
sdong cadc1adffa Refactor: group metadata needed to open an SST file to a separate copyable struct
Summary:
We added multiple fields to FileMetaData recently and are planning to add more.
This refactoring separate the minimum information for accessing the file. This object is copyable (FileMetaData is not copyable since the ref counter). I hope this refactoring can enable further improvements:

(1) use it to design a more efficient data structure to speed up read queries.
(2) in the future, when we add information of storage level, we can easily do the encoding, instead of enlarge this structure, which might expand memory work set for file meta data.

The definition is same as current EncodedFileMetaData used in two level iterator, so now the logic in two level iterator is easier to understand.

Test Plan: make all check

Reviewers: haobo, igor, ljin

Reviewed By: ljin

Subscribers: leveldb, dhruba, yhchiang

Differential Revision: https://reviews.facebook.net/D18933
2014-06-16 16:10:52 -07:00
Bradley Grainger 2d02ec6533 Add separate Read/WriteUnlock methods in MutexRW.
Some platforms, particularly Windows, do not have a single method that can
release both a held reader lock and a held writer lock; instead, a
separate method (ReleaseSRWLockShared or ReleaseSRWLockExclusive) must be
called in each case.

This may also be necessary to back MutexRW with a shared_mutex in C++14;
the current language proposal includes both an unlock() and a
shared_unlock() method.
2014-06-16 15:41:46 -07:00
sdong 983c93d731 VersionSet::Get(): Bring back the logic of skipping key range check when there are <=3 level 0 files
Summary:
https://reviews.facebook.net/D17205 removed the logic of skipping file key range check when there are less than 3 level 0 files. This patch brings it back.

Other than that, add another small optimization to avoid to check all the levels if most higher levels don't have any file.

Test Plan: make all check

Reviewers: ljin

Reviewed By: ljin

Subscribers: yhchiang, igor, haobo, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D19035
2014-06-13 15:51:44 -07:00
Lei Jin c83b085770 prefetch bloom filter data block for L0 files
Summary: as title

Test Plan:
db_bench
the initial result is very promising. I will post results of complete
runs

Reviewers: dhruba, haobo, sdong, igor

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D18867
2014-06-12 10:06:18 -07:00
Lei Jin 77db08f27b fix forward iterator bug
Summary: obvious

Test Plan: db_test

Reviewers: sdong, haobo, igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D18987
2014-06-10 09:57:26 -07:00
sdong 80f409ea37 Clean PlainTableReader's variables for better data locality
Summary:
Clean PlainTableReader's data structures:
(1) inline bloom_ (in order to do this, change DynamicBloom to allow lazy initialization)
(2) remove some variables only used when initialization from the class
(3) put variables not used in normal read code paths to the end of the class and reference prefix_extractor directly
(4) make Options a reference.

Test Plan: make all check

Reviewers: haobo, ljin

Reviewed By: ljin

Subscribers: igor, yhchiang, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D18891
2014-06-09 13:53:39 -07:00
Igor Canadi 0365eaf12e remove unnecessary printf 2014-06-06 18:27:44 -07:00
Igor Canadi a0191c9dfe Create Missing Column Families
Summary: Provide an convenience option to create column families if they are missing from the DB. Task #4460490

Test Plan: added unit test. also, stress test for some time

Reviewers: sdong, haobo, dhruba, ljin, yhchiang

Reviewed By: yhchiang

Subscribers: yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D18951
2014-06-06 18:04:56 -07:00
Igor Canadi 99d3eed2fd Write Fast-path for single column family
Summary: We have a perf regression of Write() even with one column family. Make fast path for single column family to avoid the perf regression. See task #4455480

Test Plan: make check

Reviewers: sdong, ljin

Reviewed By: sdong, ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D18963
2014-06-06 17:26:23 -07:00
sdong b92a19a431 sst_dump: Set dummy prefix extractor for binary search index in block based table
Summary: Now sst_dump fails in block based tables if binary search index is used, as it requires a prefix extractor. Add it.

Test Plan: Run it against such a file to make sure it fixes the problem.

Reviewers: yhchiang, kailiu

Reviewed By: kailiu

Subscribers: ljin, igor, dhruba, haobo, leveldb

Differential Revision: https://reviews.facebook.net/D18927
2014-06-05 15:37:23 -07:00
Igor Canadi 5d870717ae Correctly preallocate files in universal compaction
Summary: In universal compaction, MaxFileSizeForLevel is ULLONG_MAX. We've been preallocation files to UULONG_MAX size all these time :)

Test Plan: make check

Reviewers: dhruba, haobo, ljin, sdong, yhchiang

Reviewed By: yhchiang

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D18915
2014-06-05 13:19:35 -07:00
Igor Canadi fd27001072 Fix compile errors on Mac
Summary: https://phabricator.fb.com/P11372644

Test Plan: compiles

Reviewers: sdong, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D18873
2014-06-03 12:28:58 -07:00
sdong df9069d23f In DB::NewIterator(), try to allocate the whole iterator tree in an arena
Summary:
In this patch, try to allocate the whole iterator tree starting from DBIter from an arena
1. ArenaWrappedDBIter is created when serves as the entry point of an iterator tree, with an arena in it.
2. Add an option to create iterator from arena for following iterators: DBIter, MergingIterator, MemtableIterator, all mem table's iterators, all table reader's iterators and two level iterator.
3. MergeIteratorBuilder is created to incrementally build the tree of internal iterators. It is passed to mem table list and version set and add iterators to it.

Limitations:
(1) Only DB::NewIterator() without tailing uses the arena. Other cases, including readonly DB and compactions are still from malloc
(2) Two level iterator itself is allocated in arena, but not iterators inside it.

Test Plan: make all check

Reviewers: ljin, haobo

Reviewed By: haobo

Subscribers: leveldb, dhruba, yhchiang, igor

Differential Revision: https://reviews.facebook.net/D18513
2014-06-02 17:44:57 -07:00
Igor Canadi 91ddd587cc Only signal cond variable if need to
Summary:
At the end of BackgroundCallCompaction(), we call SignalAll(), even though we don't need to. If compaction hasn't done anything and there's another compaction running, there is no need to signal on the condition variable. Doing so creates a tight feedback loop which results in log files like:

   wait for memtable flush
   compaction nothing to do
   wait for memtable flush
   compaction nothing to do

This change eliminates that

Test Plan:
make check
Also:

    icanadi@dev1440 ~ $ grep "nothing to do" /fast-rocksdb-tmp/rocksdb_test/column_family_test/LOG | wc -l
    7435
    icanadi@dev1440 ~ $ grep "nothing to do" /fast-rocksdb-tmp/rocksdb_test/column_family_test/LOG | wc -l
    372

First version is before the change, second version is after the change.

Reviewers: dhruba, ljin, haobo, yhchiang, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D18855
2014-06-02 17:23:55 -07:00
Igor Canadi 8cb7ad83c3 Flush stale column families less aggressively
Summary:
We've seen some production issues where column family is detected as stale, although there is only one column family in the system. This is a quick fix that:
1) doesn't flush stale column families if there's only one of them
2) Use 4 as a coefficient instead of 2 for determening when a column family is stale. This will make flushing less aggressive, while still keep a nice dynamic flushing of very stale CFs.

Test Plan: make check

Reviewers: dhruba, haobo, ljin, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D18861
2014-06-02 15:33:54 -07:00
Lei Jin 388d2054c7 forward iterator
Summary:
Forward iterator puts everything together in a flat structure instead of
a hierarchy of nested iterators. this should simplify the code and
provide better performance. It also enables more optimization since all
information are accessiable in one place.
Init evaluation shows about 6% improvement

Test Plan: db_test and db_bench

Reviewers: dhruba, igor, tnovak, sdong, haobo

Reviewed By: haobo

Subscribers: sdong, leveldb

Differential Revision: https://reviews.facebook.net/D18795
2014-05-30 14:31:55 -07:00
Lei Jin f29c62fc6f add an iterator refresh option for SeekRandom
Summary: One more option to allow iterator refreshing when using normal iterator

Test Plan: ran db_bench

Reviewers: haobo, sdong, igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D18849
2014-05-30 14:09:22 -07:00
Igor Canadi 6de6a06631 FIFO compaction style
Summary:
Introducing new compaction style -- FIFO.

FIFO compaction style has write amplification of 1 (+1 for WAL) and it deletes the oldest files when the total DB size exceeds pre-configured values.

FIFO compaction style is suited for storing high-frequency event logs.

Test Plan: Added a unit test

Reviewers: dhruba, haobo, sdong

Reviewed By: dhruba

Subscribers: alberts, leveldb

Differential Revision: https://reviews.facebook.net/D18765
2014-05-21 11:43:35 -07:00
Igor Canadi b2cf95fe38 Call EnableFileDeletions with false as argument 2014-05-20 14:28:51 -07:00
sdong 4e0602f941 Remove maximum key_size check in db_bench
Summary: Key size limit doesn't seem to be applicable anymore. Remove it.

Test Plan: run a couple of tests in db_bench

Reviewers: haobo, igor, yhchiang, dhruba

Reviewed By: igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18723
2014-05-15 11:06:37 -07:00
Igor Canadi f4574449e9 Clean up compaction logging
Summary: Cleaned up compaction logging a little bit. Now file sizes are easier to read. Also, removed the trailing space.

Test Plan:
verified that i'm happy with logging output:

        files_size[#33(seq=101,sz=98KB,0) #31(seq=81,sz=159KB,0) #26(seq=0,sz=637KB,0)]

Reviewers: sdong, haobo, dhruba

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18549
2014-05-14 12:13:50 -07:00
sdong 3e4a9ec241 Arena to inline 2KB of data in it.
Summary:
In order to use arena to a use case that the total allocation size might be small (LogBuffer is already such a case), inline 1KB of data in it, so that it can be mostly in stack or inline in another class.

If always inlining 2KB is a concern, I could make it a template to determine what to inline. However, dependents need to changes. Doesn't go with it for now

Test Plan: make all check.

Reviewers: haobo, igor, yhchiang, dhruba

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18609
2014-05-14 11:49:01 -07:00
Igor Canadi 26f5dd9a5a TablePropertiesCollectorFactory
Summary:
This diff addresses task #4296714 and rethinks how users provide us with TablePropertiesCollectors as part of Options.

Here's description of task #4296714:
       I'm debugging #4295529 and noticed that our count of user properties kDeletedKeys is wrong. We're sharing one single InternalKeyPropertiesCollector with all Table Builders. In LOG Files, we're outputting number of kDeletedKeys as connected with a single table, while it's actually the total count of deleted keys since creation of the DB.

       For example, this table has 3155 entries and 1391828 deleted keys.

The problem with current approach that we call methods on a single TablePropertiesCollector for all the tables we create. Even worse, we could do it from multiple threads at the same time and TablePropertiesCollector has no way of knowing which table we're calling it for.

Good part: Looks like nobody inside Facebook is using Options::table_properties_collectors. This means we should be able to painfully change the API.

In this change, I introduce TablePropertiesCollectorFactory. For every table we create, we call `CreateTablePropertiesCollector`, which creates a TablePropertiesCollector for a single table. We then use it sequentially from a single thread, which means it doesn't have to be thread-safe.

Test Plan:
Added a test in table_properties_collector_test that fails on master (build two tables, assert that kDeletedKeys count is correct for the second one).
Also, all other tests

Reviewers: sdong, dhruba, haobo, kailiu

Reviewed By: kailiu

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18579
2014-05-13 12:30:55 -07:00
Yueh-Hsuan Chiang 1c7799d8aa Fixed a file-not-found issue when a log file is moved to archive.
Summary:
Fixed a file-not-found issue when a log file is moved to archive
by doing a missing retry.

Test Plan:
make db_test
export ROCKSDB_TEST=TransactionLogIteratorRace
./db_test

Reviewers: sdong, haobo

Reviewed By: sdong

CC: igor, leveldb

Differential Revision: https://reviews.facebook.net/D18669
2014-05-12 17:50:21 -07:00
sdong acd17fd002 Remove unused variable in DBIter
Summary: as title

Test Plan: Still compile

Reviewers: haobo, igor, yhchiang

Reviewed By: igor

CC: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D18603
2014-05-09 13:20:35 -07:00
Igor Canadi a1068c91a1 Make RocksDB work with newer gflags
Summary:
Newer gflags switched from `google` namespace to `gflags` namespace. See: https://github.com/facebook/rocksdb/issues/139 and https://github.com/facebook/rocksdb/issues/102

Unfortunately, they don't define any macro with their namespace, so we need to actually try to compile gflags with two different namespace to figure out which one is the correct one.

Test Plan: works in fbcode environemnt. I'll also try in ubutnu with newer gflags

Reviewers: dhruba

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18537
2014-05-08 17:25:13 -07:00
Igor Canadi 8e37a29bfb Compaction with zero outputs
Summary: We had a hypothesis in https://reviews.facebook.net/D18507 that empty-string internal keys might have been caused by compaction filter deleting all the entries. I added a unit test for that case. Unforutnately, everything works as expected.

Test Plan: this is a test

Reviewers: dhruba, haobo, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18519
2014-05-08 13:48:39 -07:00