Summary:
This patch addes ColumnFamilyHandle::GetDescriptor(), which allows
developers to obtain the CF options and names of the associated column
family given its handle.

  // Returns the up-to-date descriptor used by the current handle.  Since it
  // returns the up-to-date information, this call might internally locks
  // and releases DB mutex to access the up-to-date CF options.
  virtual ColumnFamilyDescriptor GetDescriptor() = 0;

Test Plan: augment column_family_test

Reviewers: sdong, yoshinorim, IslamAbdelRahman, rven, kradhakrishnan, anthony

Reviewed By: anthony

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D51543

Currently Windows build is broken because of Warning C4351. Disable the warning before figuring out the right way to fix it.

Summary:
This diff adds support for concurrent adds to the skiplist memtable
implementations.  Memory allocation is made thread-safe by the addition of
a spinlock, with small per-core buffers to avoid contention.  Concurrent
memtable writes are made via an additional method and don't impose a
performance overhead on the non-concurrent case, so parallelism can be
selected on a per-batch basis.

Write thread synchronization is an increasing bottleneck for higher levels
of concurrency, so this diff adds --enable_write_thread_adaptive_yield
(default off).  This feature causes threads joining a write batch
group to spin for a short time (default 100 usec) using sched_yield,
rather than going to sleep on a mutex.  If the timing of the yield calls
indicates that another thread has actually run during the yield then
spinning is avoided.  This option improves performance for concurrent
situations even without parallel adds, although it has the potential to
increase CPU usage (and the heuristic adaptation is not yet mature).

Parallel writes are not currently compatible with
inplace updates, update callbacks, or delete filtering.
Enable it with --allow_concurrent_memtable_write (and
--enable_write_thread_adaptive_yield).  Parallel memtable writes
are performance neutral when there is no actual parallelism, and in
my experiments (SSD server-class Linux and varying contention and key
sizes for fillrandom) they are always a performance win when there is
more than one thread.

Statistics are updated earlier in the write path, dropping the number
of DB mutex acquisitions from 2 to 1 for almost all cases.

This diff was motivated and inspired by Yahoo's cLSM work.  It is more
conservative than cLSM: RocksDB's write batch group leader role is
preserved (along with all of the existing flush and write throttling
logic) and concurrent writers are blocked until all memtable insertions
have completed and the sequence number has been advanced, to preserve
linearizability.

My test config is "db_bench -benchmarks=fillrandom -threads=$T
-batch_size=1 -memtablerep=skip_list -value_size=100 --num=1000000/$T
-level0_slowdown_writes_trigger=9999 -level0_stop_writes_trigger=9999
-disable_auto_compactions --max_write_buffer_number=8
-max_background_flushes=8 --disable_wal --write_buffer_size=160000000
--block_size=16384 --allow_concurrent_memtable_write" on a two-socket
Xeon E5-2660 @ 2.2Ghz with lots of memory and an SSD hard drive.  With 1
thread I get ~440Kops/sec.  Peak performance for 1 socket (numactl
-N1) is slightly more than 1Mops/sec, at 16 threads.  Peak performance
across both sockets happens at 30 threads, and is ~900Kops/sec, although
with fewer threads there is less performance loss when the system has
background work.

Test Plan:
1. concurrent stress tests for InlineSkipList and DynamicBloom
2. make clean; make check
3. make clean; DISABLE_JEMALLOC=1 make valgrind_check; valgrind db_bench
4. make clean; COMPILE_WITH_TSAN=1 make all check; db_bench
5. make clean; COMPILE_WITH_ASAN=1 make all check; db_bench
6. make clean; OPT=-DROCKSDB_LITE make check
7. verify no perf regressions when disabled

Reviewers: igor, sdong

Reviewed By: sdong

Subscribers: MarkCallaghan, IslamAbdelRahman, anthony, yhchiang, rven, sdong, guyg8, kradhakrishnan, dhruba

Differential Revision: https://reviews.facebook.net/D50589

Summary: It's usually hard for users to set a value of options.delayed_write_rate. With this diff, after slowdown condition triggers, we greedily reduce write rate if estimated pending compaction bytes increase. If estimated compaction pending bytes drop, we increase the write rate.

Test Plan:
Add a unit test
Test with db_bench setting:
TEST_TMPDIR=/dev/shm/ ./db_bench --benchmarks=fillrandom -num=10000000 --soft_pending_compaction_bytes_limit=1000000000 --hard_pending_compaction_bytes_limit=3000000000 --delayed_write_rate=100000000

and make sure without the commit, write stop will happen, but with the commit, it will not happen.

Reviewers: igor, anthony, rven, yhchiang, kradhakrishnan, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D52131

Summary: Now if inserting to mem table is much faster than writing to files, there is no mechanism users can rely on to avoid stopping for reaching options.max_write_buffer_number. With the commit, if there are more than four maximum write buffers configured, we slow down to the rate of options.delayed_write_rate while we reach the last one.

Test Plan:
1. Add a new unit test.
2. Run db_bench with

./db_bench --benchmarks=fillrandom --num=10000000 --max_background_flushes=6 --batch_size=32 -max_write_buffer_number=4 --delayed_write_rate=500000 --statistics

based on hard drive and see stopping is avoided with the commit.

Reviewers: yhchiang, IslamAbdelRahman, anthony, rven, kradhakrishnan, igor

Reviewed By: igor

Subscribers: MarkCallaghan, leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D52047

Running manual compactions in parallel with other automatic or manual compactions in restricted cases

Summary:
This diff provides a framework for doing manual
compactions in parallel with other compactions. We now have a deque of manual compactions. We also pass manual compactions as an argument from RunManualCompactions down to
BackgroundCompactions, so that RunManualCompactions can be reentrant.
Parallelism is controlled by the two routines
ConflictingManualCompaction to allow/disallow new parallel/manual
compactions based on already existing ManualCompactions. In this diff, by default manual compactions still have to run exclusive of other compactions. However, by setting the compaction option, exclusive_manual_compaction to false, it is possible to run other compactions in parallel with a manual compaction. However, we are still restricted to one manual compaction per column family at a time. All of these restrictions will be relaxed in future diffs.
I will be adding more tests later.

Test Plan: Rocksdb regression + new tests + valgrind

Reviewers: igor, anthony, IslamAbdelRahman, kradhakrishnan, yhchiang, sdong

Reviewed By: sdong

Subscribers: yoshinorim, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D47973

Summary: Deprecate options.soft_rate_limit, which is hard to tune, with options.soft_pending_compaction_bytes_limit, which would trigger the slowdown if estimated pending compaction bytes exceeds the threshold. The hope is to make it more striaght-forward to tune.

Test Plan: Modify DBTest.SoftLimit to cover options.soft_pending_compaction_bytes_limit instead; run all unit tests.

Reviewers: IslamAbdelRahman, yhchiang, rven, kradhakrishnan, igor, anthony

Reviewed By: anthony

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D51117

Summary:
Currently RocksDB may break in lines like this:

for (size_t i = sorted_runs.size() - 1; i >= first_index_after; i--) {

if options.level0_file_num_compaction_trigger=0.

Fix it by not executing the logic of picking compactions if there is no file (sorted_runs.size() = 0). Also internally set options.level0_file_num_compaction_trigger=1 if users give a 0. 0 is a value makes no sense in RocksDB.

Test Plan: Run all tests. Will add a unit test too.

Reviewers: yhchiang, IslamAbdelRahman, anthony, kradhakrishnan, rven

Reviewed By: rven

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D50727

Summary:
We are cleaning up dependencies.
This diff takes a first step at moving memtable files to their own
directory called memtable. In future diffs, we will move other memtable
files from db to memtable.

Test Plan: make check

Reviewers: sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D48915

Summary: Add an option to stop writes if compaction lefts behind. If estimated pending compaction bytes is more than threshold specified by options.hard_pending_compaction_bytes_liimt, writes will stop until compactions are cleared to under the threshold.

Test Plan: Add unit test DBTest.HardLimit

Reviewers: rven, kradhakrishnan, anthony, IslamAbdelRahman, yhchiang, igor

Reviewed By: igor

Subscribers: MarkCallaghan, leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D45999

Summary:
Although there are currently counters to keep track of the
stall caused by having too many L0 files, there is no distinction as
to whether when that stall occurs either (A) L0-L1 compaction is taking
place to try and mitigate it, or (B) no L0-L1 compaction has been scheduled
at the moment. This diff adds a counter for (A) so that the nature of L0
stalls can be better understood.

Test Plan: make all && make check

Reviewers: sdong, igor, anthony, noetzli, yhchiang

Reviewed By: yhchiang

Subscribers: MarkCallaghan, dhruba

Differential Revision: https://reviews.facebook.net/D46749

Summary: Currently, if users didn't set options.arena_block_size, we set "result.arena_block_size = result.write_buffer_size / 10". It makes result.arena_block_size not a multiplier of 4KB, even if options.write_buffer_size is a multiplier of MBs. When calling malloc to arena_block_size, we may waste a small amount of memory for it. We now make the default to be /8 or /16 and align it to 4KB.

Test Plan: unit tests

Reviewers: sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D46467

Summary: Add a new DB property that calculate the total size of files used by all RocksDB Versions

Test Plan: Unittests for the new property

Reviewers: igor, yhchiang, anthony, rven, kradhakrishnan, sdong

Reviewed By: sdong

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D44799

Summary:
Currently, GetIntProperty("rocksdb.cur-size-all-mem-tables") only returns
the memory usage by those memtables which have not yet been flushed.

This patch introduces GetIntProperty("rocksdb.size-all-mem-tables"),
which includes the memory usage by all the memtables, includes those
have been flushed but pinned by iterators.

Test Plan: Added a test in db_test

Reviewers: igor, anthony, IslamAbdelRahman, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D44229

Summary:
When we first started, max_background_flushes was 0 by default and compaction thread was executing flushes (since there was no flush thread). Then, we switched the default max_background_flushes to 1. However, we still support the case where there is no flush thread and flushes are done in compaction. This is making our code a bit more complicated. By not supporting this use-case we can make our code simpler.

We have a special case that when you set max_background_flushes to 0, we
schedule the flush to execute on the compaction thread.

Test Plan: make check (there might be some unit tests that depend on this behavior)

Reviewers: IslamAbdelRahman, yhchiang, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D41931

Summary: Fixes valgrind errors in column_family_test.

Test Plan: `make check`, `make valgrind_check`

Reviewers: igor, yhchiang

Reviewed By: yhchiang

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D41181

Summary:
Currently RocksDB silently ignores this issue and doesn't compress the data. Based on discussion, we agree that this is pretty bad because it can cause confusion for our users.

This patch fails DB::Open() if we don't support the compression that is specified in the options.

Test Plan: make check with LZ4 not present. If Snappy is not present all tests will just fail because Snappy is our default library. We should make Snappy the requirement, since without it our default DB::Open() fails.

Reviewers: sdong, MarkCallaghan, rven, yhchiang

Reviewed By: yhchiang

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D39687

Summary: Currently we dump DBOptions for each column family options we dump. This leads to duplicate lines in our LOG file. This diff fixes that.

Test Plan: Check out the LOG

Reviewers: sdong, rven, yhchiang

Reviewed By: yhchiang

Subscribers: IslamAbdelRahman, yoshinorim, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D39729

Summary:
We slow down data into the database to the rate of options.delayed_write_rate (a new option) with this patch.

The thread synchronization approach I take is to still synchronize write controller by DB mutex and GetDelay() is inside DB mutex. Try to minimize the frequency of getting time in GetDelay(). I verified it through db_bench and it seems to work

hard_rate_limit is deprecated.

options.delayed_write_rate is still not dynamically changeable. Need to work on it as a follow-up.

Test Plan: Add new unit tests in db_test

Reviewers: yhchiang, rven, kradhakrishnan, anthony, MarkCallaghan, igor

Reviewed By: igor

Subscribers: ikabiljo, leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D36351

Summary:
Allow EventListener::OnCompactionCompleted to return CompactionJobStats,
which contains useful information about a compaction.

Example CompactionJobStats returned by OnCompactionCompleted():
    smallest_output_key_prefix 05000000
    largest_output_key_prefix 06990000
    elapsed_time 42419
    num_input_records 300
    num_input_files 3
    num_input_files_at_output_level 2
    num_output_records 200
    num_output_files 1
    actual_bytes_input 167200
    actual_bytes_output 110688
    total_input_raw_key_bytes 5400
    total_input_raw_value_bytes 300000
    num_records_replaced 100
    is_manual_compaction 1

Test Plan: Developed a mega test in db_test which covers 20 variables in CompactionJobStats.

Reviewers: rven, igor, anthony, sdong

Reviewed By: sdong

Subscribers: tnovak, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D38463

Summary: Optimistic transactions supporting begin/commit/rollback semantics.  Currently relies on checking the memtable to determine if there are any collisions at commit time.  Not yet implemented would be a way of enuring the memtable has some minimum amount of history so that we won't fail to commit when the memtable is empty.  You should probably start with transaction.h to get an overview of what is currently supported.

Test Plan: Added a new test, but still need to look into stress testing.

Reviewers: yhchiang, igor, rven, sdong

Reviewed By: sdong

Subscribers: adamretter, MarkCallaghan, leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D33435

Summary:
For transactions, we are using the memtables to validate that there are no write conflicts.  But after flushing, we don't have any memtables, and transactions could fail to commit.  So we want to someone keep around some extra history to use for conflict checking.  In addition, we want to provide a way to increase the size of this history if too many transactions fail to commit.

After chatting with people, it seems like everyone prefers just using Memtables to store this history (instead of a separate history structure).  It seems like the best place for this is abstracted inside the memtable_list.  I decide to create a separate list in MemtableListVersion as using the same list complicated the flush/installalflushresults logic too much.

This diff adds a new parameter to control how much memtable history to keep around after flushing.  However, it sounds like people aren't too fond of adding new parameters.  So I am making the default size of flushed+not-flushed memtables be set to max_write_buffers.  This should not change the maximum amount of memory used, but make it more likely we're using closer the the limit.  (We are now postponing deleting flushed memtables until the max_write_buffer limit is reached).  So while we might use more memory on average, we are still obeying the limit set (and you could argue it's better to go ahead and use up memory now instead of waiting for a write stall to happen to test this limit).

However, if people are opposed to this default behavior, we can easily set it to 0 and require this parameter be set in order to use transactions.

Test Plan: Added a xfunc test to play around with setting different values of this parameter in all tests.  Added testing in memtablelist_test and planning on adding more testing here.

Reviewers: sdong, rven, igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D37443

Summary: Move listeners from ColumnFamilyOptions to DBOptions

Test Plan:
listener_test
compact_files_test

Reviewers: rven, anthony, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D39087

Summary: Ensure ColumnFamilyOptions.num_levels >= 2 when level compaction is used.

Test Plan: Extend SanitizeOptions test in column_family_test

Reviewers: sdong, rven, anthony, krishnanm86, igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D38829

Summary: CompactRange() now is much more expensive for dynamic level base size as it goes through all the levels. Skip those not used levels between level 0 an base level.

Test Plan: Run all unit tests

Reviewers: yhchiang, rven, anthony, kradhakrishnan, igor

Reviewed By: igor

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D37125

Summary:
Fixed the following compile error in db/column_family.cc
    db/column_family.cc:633:33: error: ‘ASSERT_GT’ was not declared in this scope
    16:14:45    ASSERT_GT(listeners.size(), 0U);

Test Plan: make db_test

Reviewers: igor, sdong, rven

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D38367

Summary:
Fixed a bug in EventListener::OnCompactionCompleted() that returns
incorrect list of input / output file names.

Test Plan: Extend existing test in listener_test.cc

Reviewers: sdong, rven, igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D38349

Summary:
CompactRange for universal compaction with num_levels > 1 seems to have a bug. The unit test also has a bug so it doesn't capture the problem.
Fix it. Revert the compact range to the logic equivalent to num_levels=1. Always compact all files together.

It should also fix DBTest.IncreaseUniversalCompactionNumLevels. The issue was that options.write_buffer_size = 100 << 10 and options.write_buffer_size = 100 << 10 are not used in later test scenarios. So write_buffer_size of 4MB was used. The compaction trigger condition is not anymore obvious as expected.

Test Plan: Run the new test and all test suites

Reviewers: yhchiang, rven, kradhakrishnan, anthony, igor

Reviewed By: igor

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D37551

Summary: Now we add warnings when user configures compression and the compression is not supported.

Test Plan:
Configured compression to non-supported values. Observed messages in my log:

    2015/03/26-12:17:57.586341 7ffb8a496840 [WARN] Compression type chosen for level 2 is not supported: LZ4. RocksDB will not compress data on level 2.

    2015/03/26-12:19:10.768045 7f36f15c5840 [WARN] Compression type chosen is not supported: LZ4. RocksDB will not compress data.

Reviewers: rven, sdong, yhchiang

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D35979

Summary:
Currently users have no idea a key is add, delete or merge from TablePropertiesCollector call back. Add a new function to add it.

Also refactor the codes so that
(1) make table property collector and internal table property collector two separate data structures with the later one now exposed
(2) table builders only receive internal table properties

Test Plan: Add cases in table_properties_collector_test to cover both of old and new ways of using TablePropertiesCollector.

Reviewers: yhchiang, igor.sugak, rven, igor

Reviewed By: rven, igor

Subscribers: meyering, yoshinorim, maykov, leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D35373

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:
Per-level stall times are the suggested stall time, not the actual stall time so this change stops printing them
both in the per-level output lines and in the summary. Also changed output for total stall time to include units
in all cases. The new output looks like:
Level   Files   Size(MB) Score Read(GB)  Rn(GB) Rnp1(GB) Write(GB) Wnew(GB) Moved(GB) W-Amp Rd(MB/s) Wr(MB/s) Comp(sec) Comp(cnt) Avg(sec) Stall(cnt)    RecordIn   RecordDrop
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  L0     4/1          7   0.8      0.0     0.0      0.0       0.6      0.6       0.0   0.0      0.0     12.9        50       352    0.141        882            0            0
  L1     5/0          9   0.9      0.0     0.0      0.0       0.0      0.0       0.6   0.0      0.0      0.0         0         0    0.000          0            0            0
  L2    54/0         99   1.0      0.0     0.0      0.0       0.0      0.0       0.6   0.0      0.0      0.0         0         0    0.000          0            0            0
  L3   289/0        527   0.5      0.0     0.0      0.0       0.0      0.0       0.5   0.0      0.0      0.0         0         0    0.000          0            0            0
 Sum   352/1        642   0.0      0.0     0.0      0.0       0.6      0.6       1.7   1.0      0.0     12.9        50       352    0.141        882            0            0
 Int     0/0          0   0.0      0.0     0.0      0.0       0.0      0.0       0.0   1.0      0.0     15.5         0         3    0.118          7            0            0
Flush(GB): accumulative 0.627, interval 0.005
Stalls(count): 0 level0_slowdown, 0 level0_numfiles, 882 memtable_compaction, 0 leveln_slowdown_soft, 0 leveln_slowdown_hard

Task ID: #6493861

Blame Rev:

Test Plan:
run db_bench, look at output

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/D35085

options.level_compaction_dynamic_level_bytes to allow RocksDB to pick size bases of levels dynamically.

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

Test Plan: Run "make clean && make all check"

Reviewers: rven, igor, yhchiang, kradhakrishnan, MarkCallaghan, sdong

Reviewed By: sdong

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D33627

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:
It would be good to assing background job their IDs. Two benefits:
1) makes LOGs more readable
2) I might use it in my EventLogger, which will try to make our LOG easier to read/query/visualize

Test Plan: ran rocksdb, read the LOG

Reviewers: sdong, rven, yhchiang

Reviewed By: yhchiang

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D31617

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: This adds a listener for compactions, and gives some useful statistics on each compaction pass.

Test Plan: Unit tests.

Reviewers: sdong, igor, rven, yhchiang

Reviewed By: yhchiang

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D31641

Summary: I'm not sure the expected results of std::atomic::fetch_sub() when using memory_order_relaxed, and I suspect TSAN complains.

Test Plan: make all check

Reviewers: rven, yhchiang, igor

Reviewed By: igor

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D32259