Summary:
There is an existing field Options.max_bytes_for_level_multiplier that
sets the multiplier for the size of each level in the database.
This patch introduces the ability to set different multipliers
for every level in the database. The size of a level is determined
by using both max_bytes_for_level_multiplier as well as the
per-level fanout.
size of level[i] = size of level[i-1] * max_bytes_for_level_multiplier
* fanout[i-1]
The default value of fanout is 1, so that it is backward compatible.
Test Plan: make check
Reviewers: haobo, emayanke
Reviewed By: emayanke
CC: leveldb
Differential Revision: https://reviews.facebook.net/D10863
Summary:
The merge operator diff introduced a performance problem in MemTable::Get.
An exit condition is missed when the current key does not match the user key.
This could lead to full memtable scan if the user key is not found.
Test Plan: make check; db_bench
Reviewers: dhruba
Reviewed By: dhruba
CC: leveldb
Differential Revision: https://reviews.facebook.net/D10851
Summary:
Make stop watch a simple implementation, instead of subclass of a virtual class
Allocate stop watches off the stack instead of heap.
Code is more terse now.
Test Plan: make all check, db_bench with --statistics=1
Reviewers: haobo, dhruba
Reviewed By: haobo
CC: leveldb
Differential Revision: https://reviews.facebook.net/D10809
Summary: Statistics.h and histogram.h had double based api's to record values. Remove them as they are not used anywhere
Test Plan: make all check
Reviewers: haobo, dhruba
Reviewed By: haobo
CC: leveldb
Differential Revision: https://reviews.facebook.net/D10815
Summary:
This diff replaces compaction_filter_args and CompactionFilter with a single compaction_filter parameter. It gives CompactionFilter better encapsulation and a similar look to Comparator and MergeOpertor, which improves consistency of the overall interface.
The change is not backward compatible. Nevertheless, the two references in fbcode are not in production yet.
Test Plan: make check
Reviewers: dhruba
Reviewed By: dhruba
CC: leveldb, zshao
Differential Revision: https://reviews.facebook.net/D10773
Summary:
Currently, compaction filter is run on internal key older than the oldest snapshot, which is incorrect.
Compaction filter should really be run on the most recent internal key when there is no external snapshot.
Test Plan: make check; db_stress
Reviewers: dhruba
Reviewed By: dhruba
Differential Revision: https://reviews.facebook.net/D10641
Summary:
For level-0 compactions, we try to find if can include more L0 files
in the same compaction run. This causes the 'smallest' and 'largest'
key to get extended to a larger range. But the suceeding call to
ParentRangeInCompaction() was still using the earlier
values of 'smallest' and 'largest',
Because of this bug, a file in L1 can be part of two concurrent
compactions: one L0-L1 compaction and the other L1-L2 compaction.
This should not cause any data loss, but will cause an assertion
failure with debug builds.
Test Plan: make check
Differential Revision: https://reviews.facebook.net/D10677
Summary:
WAL files are moved to archive directory and clear only at DB::Open.
Can lead to a lot of space consumption in a Database. Added logic to periodically clear Archive Directory too.
Test Plan: make all check + add unit test
Reviewers: dhruba, heyongqiang
Reviewed By: heyongqiang
CC: leveldb
Differential Revision: https://reviews.facebook.net/D10617
Summary:
This diff introduces a new Merge operation into rocksdb.
The purpose of this review is mostly getting feedback from the team (everyone please) on the design.
Please focus on the four files under include/leveldb/, as they spell the client visible interface change.
include/leveldb/db.h
include/leveldb/merge_operator.h
include/leveldb/options.h
include/leveldb/write_batch.h
Please go over local/my_test.cc carefully, as it is a concerete use case.
Please also review the impelmentation files to see if the straw man implementation makes sense.
Note that, the diff does pass all make check and truly supports forward iterator over db and a version
of Get that's based on iterator.
Future work:
- Integration with compaction
- A raw Get implementation
I am working on a wiki that explains the design and implementation choices, but coding comes
just naturally and I think it might be a good idea to share the code earlier. The code is
heavily commented.
Test Plan: run all local tests
Reviewers: dhruba, heyongqiang
Reviewed By: dhruba
CC: leveldb, zshao, sheki, emayanke, MarkCallaghan
Differential Revision: https://reviews.facebook.net/D9651
Summary:
The current code has a bug that take address of stack allocated LogReporter.
It is causing SIGSEGV because the stack address is no longer valid when referenced.
Test Plan: Tested on prod.
Reviewers: haobo, dhruba, heyongqiang
Reviewed By: heyongqiang
Differential Revision: https://reviews.facebook.net/D10557
Summary: $title
Test Plan: make db_bench . run db_bench and check for expected output
Reviewers: haobo, dhruba
Reviewed By: haobo
CC: leveldb
Differential Revision: https://reviews.facebook.net/D10521
Summary:
- don't see a point exposing table.h to the public.
- fixed make clean to remove also *.d files.
Test Plan: make check; db_stress
Reviewers: dhruba, heyongqiang
Reviewed By: dhruba
CC: leveldb
Differential Revision: https://reviews.facebook.net/D10479
Summary: D8943 Broke read_missing. Fix it by adding a "." at the end of the generated key
Test Plan: generate, print and check the key has a "."
Reviewers: dhruba, haobo
Reviewed By: dhruba
CC: leveldb
Differential Revision: https://reviews.facebook.net/D10455
Summary:
- removed the compaction_filter_value from the callback interface. Restrict compaction filter to purging values.
- modify some comments to reflect curent status.
Test Plan: make check
Reviewers: dhruba
Reviewed By: dhruba
CC: leveldb
Differential Revision: https://reviews.facebook.net/D10335
Summary:
Adds the --writes_per_second rate limit for the readwhilewriting test.
The purpose is to optionally avoid saturating storage with writes & compaction
and test read response time when some writes are being done.
Changes the histogram code to also print the p99.99 value
Task ID: #
Blame Rev:
Test Plan:
make check, ran db_bench with it
Revert Plan:
Database Impact:
Memcache Impact:
Other Notes:
EImportant:
- begin *PUBLIC* platform impact section -
Bugzilla: #
- end platform impact -
Reviewers: haobo
Reviewed By: haobo
CC: leveldb
Differential Revision: https://reviews.facebook.net/D10305
Summary:
This diff provides the ability to print out a stacktrace when the process receives certain signals.
Currently, we enable this for the following signals (program error related):
SIGILL SIGSEGV SIGBUS SIGABRT
Application simply #include "util/stack_trace.h" and call leveldb::InstallStackTraceHandler() during initialization, if signal handler is needed. It's not done automatically when openning db, because it's the application(process)'s responsibility to install signal handler and some applications might already have their own (like fbcode).
Sample output:
Received signal 11 (Segmentation fault)
#0 0x408ff0 ./signal_test() [0x408ff0] /home/haobo/rocksdb/util/signal_test.cc:4
#1 0x40827d ./signal_test() [0x40827d] /home/haobo/rocksdb/util/signal_test.cc:24
#2 0x7f8bb183172e /usr/local/fbcode/gcc-4.7.1-glibc-2.14.1/lib/libc.so.6(__libc_start_main+0x10e) [0x7f8bb183172e] ??:0
#3 0x408ebc ./signal_test() [0x408ebc] /home/engshare/third-party/src/glibc/glibc-2.14.1/glibc-2.14.1/csu/../sysdeps/x86_64/elf/start.S:113
Segmentation fault (core dumped)
For each frame, we print the raw pointer, the symbol provided by backtrace_symbols (still not good enough), and the source file/line. Note that address translation is done by directly shell out to addr2line. ??:0 means addr2line fails to do the translation. Hacky, but I think it's good for now.
Test Plan: signal_test.cc
Reviewers: dhruba, MarkCallaghan
Reviewed By: dhruba
CC: leveldb
Differential Revision: https://reviews.facebook.net/D10173
Summary: A better error message. A local change. Did not look at other places where this could be done.
Test Plan: compile
Reviewers: dhruba, MarkCallaghan
Reviewed By: dhruba
CC: leveldb
Differential Revision: https://reviews.facebook.net/D10251
Summary: Simplified level_ptrs by using a std:vector
Test Plan: make check
Reviewers: sheki, emayanke
Reviewed By: emayanke
CC: leveldb
Differential Revision: https://reviews.facebook.net/D10245
Summary:
FindObsoleteFiles was slow, holding the single big lock, resulted in bad p99 behavior.
Didn't profile anything, but several things could be improved:
1. VersionSet::AddLiveFiles works with std::set, which is by itself slow (a tree).
You also don't know how many dynamic allocations occur just for building up this tree.
switched to std::vector, also added logic to pre-calculate total size and do just one allocation
2. Don't see why env_->GetChildren() needs to be mutex proteced, moved to PurgeObsoleteFiles where
mutex could be unlocked.
3. switched std::set to std:unordered_set, the conversion from vector is also inside PurgeObsoleteFiles
I have a feeling this should pretty much fix it.
Test Plan: make check; db_stress
Reviewers: dhruba, heyongqiang, MarkCallaghan
Reviewed By: dhruba
CC: leveldb, zshao
Differential Revision: https://reviews.facebook.net/D10197
Summary: using unique_ptr to have automatic delete for probableWALfiles in db_impl.cc
Test Plan: make
Reviewers: sheki, dhruba
Reviewed By: sheki
CC: leveldb
Differential Revision: https://reviews.facebook.net/D10083
Summary:
The segfault was happening because the program was unable to open a new
sst file (as part of the compaction) because the process ran out of
file descriptors.
The fix is to check the return status of the file creation before taking
any other action.
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fabf03f9700 (LWP 29904)]
leveldb::DBImpl::OpenCompactionOutputFile (this=this@entry=0x7fabf9011400, compact=compact@entry=0x7fabf741a2b0) at db/db_impl.cc:1399
1399 db/db_impl.cc: No such file or directory.
(gdb) where
Test Plan: make check
Reviewers: MarkCallaghan, sheki
Reviewed By: MarkCallaghan
CC: leveldb
Differential Revision: https://reviews.facebook.net/D10101
Summary:
Transaction Log Iterator did not move to the next file in the series if there was a write batch at the end of the currentFile.
The solution is if the last seq no. of the current file is < RequestedSeqNo. Assume the first seqNo. of the next file has to satisfy the request.
Also major refactoring around the code. Moved opening the logreader to a seperate function, got rid of goto.
Test Plan: added a unit test for it.
Reviewers: dhruba, heyongqiang
Reviewed By: heyongqiang
CC: leveldb, emayanke
Differential Revision: https://reviews.facebook.net/D10029
Summary:
TableAndFile was a struct used earlier to delete the file as we did not have std::unique_ptr in the codebase.
With Chip introducing C++11 hotness like std::unique_ptr we can do away with the struct.
Test Plan: make all check
Reviewers: haobo, heyongqiang
Reviewed By: heyongqiang
CC: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D9975
Summary:
During recovery, last_updated_manifest number was not set if there were no records in the Write-ahead log.
Now check for the recovered manifest also and set last_updated_manifest file to the max value.
Test Plan: unit test
Reviewers: heyongqiang
Reviewed By: heyongqiang
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9891
Summary:
If a class owns an object:
- If the object can be null => use a unique_ptr. no delete
- If the object can not be null => don't even need new, let alone delete
- for runtime sized array => use vector, no delete.
Test Plan: make check
Reviewers: dhruba, heyongqiang
Reviewed By: heyongqiang
CC: leveldb, zshao, sheki, emayanke, MarkCallaghan
Differential Revision: https://reviews.facebook.net/D9783
Summary:
RocksDB does a binary search to look at the files which might contain the requested sequence number at the call GetUpdatesSince.
There was a bug in the binary search => when the file pointed by the middle index of bsearch was empty/corrupt it needst to resize the vector and update indexes.
This now fixes that.
Test Plan: existing unit tests pass.
Reviewers: heyongqiang, dhruba
Reviewed By: heyongqiang
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9777
Summary:
If the vector returned by GetUpdatesSince is empty, it is still returned to the
user. This causes it throw an std::range error.
The probable file list is checked and it returns an IOError status instead of OK now.
Test Plan: added a unit test.
Reviewers: dhruba, heyongqiang
Reviewed By: heyongqiang
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9771
Summary:
Use non mmapd files for Write-Ahead log.
Earlier use of MMaped files. made the log iterator read ahead and miss records.
Now the reader and writer will point to the same physical location.
There is no perf regression :
./db_bench --benchmarks=fillseq --db=/dev/shm/mmap_test --num=$(million 20) --use_existing_db=0 --threads=2
with This diff :
fillseq : 10.756 micros/op 185281 ops/sec; 20.5 MB/s
without this dif :
fillseq : 11.085 micros/op 179676 ops/sec; 19.9 MB/s
Test Plan: unit test included
Reviewers: dhruba, heyongqiang
Reviewed By: heyongqiang
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9741
Summary:
Earlier Statistics object was a raw pointer. This meant the user had to clear up
the Statistics object after creating the database. In most use cases the database is created in a function and the statistics pointer is out of scope. Hence the statistics object would never be deleted.
Now Using a shared_ptr to manage this.
Want this in before the next release.
Test Plan: make all check.
Reviewers: dhruba, emayanke
Reviewed By: emayanke
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9735
Summary: rocksdb uses a single global lock to protect in memory metadata. We should minimize the mutex protected code section to increase the effective parallelism of the program. See https://our.intern.facebook.com/intern/tasks/?t=2218928
Test Plan:
make check
db_bench
Reviewers: dhruba, heyongqiang
CC: zshao, leveldb
Differential Revision: https://reviews.facebook.net/D9705
Summary:
The unit test fails as our solution does not work with MMap'd files.
Disable the failing unit test. Put it back with the next diff which should fix the problem.
Test Plan: db_test
Reviewers: heyongqiang
CC: dhruba
Differential Revision: https://reviews.facebook.net/D9645
Summary:
* Add a method to check if the log reader is at EOF.
* If we know a record has been flushed force the log_reader to believe it is not at EOF, using a new method UnMarkEof().
This does not work with MMpaed files.
Test Plan: added a unit test.
Reviewers: dhruba, heyongqiang
Reviewed By: heyongqiang
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9567
Summary:
The events that trigger compaction:
* opening the database
* Get -> only if seek compaction is not disabled and other checks are true
* MakeRoomForWrite -> when memtable is full
* BackgroundCall ->
If the background thread is about to do a compaction run, it schedules
a new background task to trigger a possible compaction. This will cause
additional background threads to find and process other compactions that
can run concurrently.
Test Plan: ran db_bench with overwrite and readonly alternatively.
Reviewers: sheki, MarkCallaghan
Reviewed By: sheki
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9579
Summary:
This patch allows an application to specify whether to use bufferedio,
reads-via-mmaps and writes-via-mmaps per database. Earlier, there
was a global static variable that was used to configure this functionality.
The default setting remains the same (and is backward compatible):
1. use bufferedio
2. do not use mmaps for reads
3. use mmap for writes
4. use readaheads for reads needed for compaction
I also added a parameter to db_bench to be able to explicitly specify
whether to do readaheads for compactions or not.
Test Plan: make check
Reviewers: sheki, heyongqiang, MarkCallaghan
Reviewed By: sheki
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9429
Summary: Some comparisons left in log_test.cc and db_test.cc complained by make
Test Plan: make
Reviewers: dhruba, sheki
Reviewed By: dhruba
Differential Revision: https://reviews.facebook.net/D9537
Summary: Makefile had options to ignore sign-comparisons and unused-parameters, which should be there. Also fixed the specific errors in the code-base
Test Plan: make
Reviewers: chip, dhruba
Reviewed By: dhruba
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9531
Summary:
Add --benchmarks=levelstats option to report per-level stats (#files, #bytes)
Change readwhilewriting test to report response time for writes but exclude
them from the stats merged by all threads.
Prevent "NaN" in stats output by preventing division by 0.
Remove "o" file I committed by mistake.
Task ID: #
Blame Rev:
Test Plan:
make check
Revert Plan:
Database Impact:
Memcache Impact:
Other Notes:
EImportant:
- begin *PUBLIC* platform impact section -
Bugzilla: #
- end platform impact -
Reviewers: dhruba
Reviewed By: dhruba
Differential Revision: https://reviews.facebook.net/D9513
Summary:
Rocksdb can create 0 sized log files when it is opened and closed without any operations.
The GetUpdatesSince fails currently if there is a log file of size zero.
This diff fixes this. If there is a log file is 0, it is removed form the probable_file_list
Test Plan: unit test
Reviewers: dhruba, heyongqiang
Reviewed By: heyongqiang
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9507
Summary:
Instead of checking for number of files in L0. Check for number of files in the requested level.
Bug introduced in D4929 (diff trying to do too many things).
Test Plan: db_test.
Reviewers: dhruba, MarkCallaghan
Reviewed By: dhruba
Differential Revision: https://reviews.facebook.net/D9483
Summary:
Add --benchmarks=updaterandom for read-modify-write workloads. This is different
from --benchmarks=readrandomwriterandom in a few ways. First, an "operation" is the
combined time to do the read & write rather than treating them as two ops. Second,
the same key is used for the read & write.
Change RandomGenerator to support rows larger than 1M. That was using "assert"
to fail and assert is compiled-away when -DNDEBUG is used.
Add more options to db_bench
--duration - sets the number of seconds for tests to run. When not set the
operation count continues to be the limit. This is used by random operation
tests.
--use_snapshot - when set GetSnapshot() is called prior to each random read.
This is to measure the overhead from using snapshots.
--get_approx - when set GetApproximateSizes() is called prior to each random
read. This is to measure the overhead for a query optimizer.
Task ID: #
Blame Rev:
Test Plan:
run db_bench
Revert Plan:
Database Impact:
Memcache Impact:
Other Notes:
EImportant:
- begin *PUBLIC* platform impact section -
Bugzilla: #
- end platform impact -
Reviewers: dhruba
Reviewed By: dhruba
Differential Revision: https://reviews.facebook.net/D9267
Summary: Fix for memory leaks in rocksdb tests. Also modified the variable NUM_FAILED_TESTS to print the actual number of failed tests.
Test Plan: make <test>; valgrind --leak-check=full ./<test>
Reviewers: sheki, dhruba
Reviewed By: sheki
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9333
Summary:
SizeBeingCompacted was called without any lock protection. This causes
crashes, especially when running db_bench with value_size=128K.
The fix is to compute SizeUnderCompaction while holding the mutex and
passing in these values into the call to Finalize.
(gdb) where
#4 leveldb::VersionSet::SizeBeingCompacted (this=this@entry=0x7f0b490931c0, level=level@entry=4) at db/version_set.cc:1827
#5 0x000000000043a3c8 in leveldb::VersionSet::Finalize (this=this@entry=0x7f0b490931c0, v=v@entry=0x7f0b3b86b480) at db/version_set.cc:1420
#6 0x00000000004418d1 in leveldb::VersionSet::LogAndApply (this=0x7f0b490931c0, edit=0x7f0b3dc8c200, mu=0x7f0b490835b0, new_descriptor_log=<optimized out>) at db/version_set.cc:1016
#7 0x00000000004222b2 in leveldb::DBImpl::InstallCompactionResults (this=this@entry=0x7f0b49083400, compact=compact@entry=0x7f0b2b8330f0) at db/db_impl.cc:1473
#8 0x0000000000426027 in leveldb::DBImpl::DoCompactionWork (this=this@entry=0x7f0b49083400, compact=compact@entry=0x7f0b2b8330f0) at db/db_impl.cc:1757
#9 0x0000000000426690 in leveldb::DBImpl::BackgroundCompaction (this=this@entry=0x7f0b49083400, madeProgress=madeProgress@entry=0x7f0b41bf2d1e, deletion_state=...) at db/db_impl.cc:1268
#10 0x0000000000428f42 in leveldb::DBImpl::BackgroundCall (this=0x7f0b49083400) at db/db_impl.cc:1170
#11 0x000000000045348e in BGThread (this=0x7f0b49023100) at util/env_posix.cc:941
#12 leveldb::(anonymous namespace)::PosixEnv::BGThreadWrapper (arg=0x7f0b49023100) at util/env_posix.cc:874
#13 0x00007f0b4a7cf10d in start_thread (arg=0x7f0b41bf3700) at pthread_create.c:301
#14 0x00007f0b49b4b11d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:115
Test Plan:
make check
I am running db_bench with a value size of 128K to see if the segfault is fixed.
Reviewers: MarkCallaghan, sheki, emayanke
Reviewed By: sheki
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9279
Summary:
If there is an error while writing an edit to the manifest file, the manifest
file is closed and reopened to check if the edit made it in. However, if the
re-opening of the manifest is unsuccessful and options.paranoid_checks is set
t true, then the db refuses to accept new puts, effectively putting the db
in readonly mode.
In a future diff, I would like to make the default value of paranoid_check
to true.
Test Plan: make check
Reviewers: sheki
Reviewed By: sheki
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9201
Summary:
Store the last flushed, seq no. in db_impl. Check against it in
transaction Log iterator. Do not attempt to read ahead if we do not know
if the data is flushed completely.
Does not work if flush is disabled. Any ideas on fixing that?
* Minor change, iter->Next is called the first time automatically for
* the first time.
Test Plan:
existing test pass.
More ideas on testing this?
Planning to run some stress test.
Reviewers: dhruba, heyongqiang
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9087
Summary:
The compaction process zeros out sequence numbers if the output is
part of the bottommost level.
The Slice is supposed to refer to an immutable data buffer. The
merger that implements the priority queue while reading kvs as
the input of a compaction run reies on this fact. The bug was that
were updating the sequence number of a record in-place and that was
causing suceeding invocations of the merger to return kvs in
arbitrary order of sequence numbers.
The fix is to copy the key to a local memory buffer before setting
its seqno to 0.
Test Plan:
Set Options.purge_redundant_kvs_while_flush = false and then run
db_stress --ops_per_thread=1000 --max_key=320
Reviewers: emayanke, sheki
Reviewed By: emayanke
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9147
Summary:
TableCache->file is not used. remove it.
I kept the TableAndFile structure and will clean it up in a future patch.
Test Plan: make clean check
Reviewers: sheki, chip
Reviewed By: chip
CC: leveldb
Differential Revision: https://reviews.facebook.net/D9075
Summary:
This adds the rate_delay_limit_milliseconds option to make the delay
configurable in MakeRoomForWrite when the max compaction score is too high.
This delay is called the Ln slowdown. This change also counts the Ln slowdown
per level to make it possible to see where the stalls occur.
From IO-bound performance testing, the Level N stalls occur:
* with compression -> at the largest uncompressed level. This makes sense
because compaction for compressed levels is much
slower. When Lx is uncompressed and Lx+1 is compressed
then files pile up at Lx because the (Lx,Lx+1)->Lx+1
compaction process is the first to be slowed by
compression.
* without compression -> at level 1
Task ID: #1832108
Blame Rev:
Test Plan:
run with real data, added test
Revert Plan:
Database Impact:
Memcache Impact:
Other Notes:
EImportant:
- begin *PUBLIC* platform impact section -
Bugzilla: #
- end platform impact -
Reviewers: dhruba
Reviewed By: dhruba
Differential Revision: https://reviews.facebook.net/D9045
Summary:
Rocks accumulates recent writes and deletes in the in-memory memtable.
When the memtable is full, it writes the contents on the memtable to
a file in L0.
This patch removes redundant records at the time of the flush. If there
are multiple versions of the same key in the memtable, then only the
most recent one is dumped into the output file. The purging of
redundant records occur only if the most recent snapshot is earlier
than the earliest record in the memtable.
Should we switch on this feature by default or should we keep this feature
turned off in the default settings?
Test Plan: Added test case to db_test.cc
Reviewers: sheki, vamsi, emayanke, heyongqiang
Reviewed By: sheki
CC: leveldb
Differential Revision: https://reviews.facebook.net/D8991
Dhruba Borthakur