Summary:
* Add a benchmark for java binding for rocksdb.  The java benchmark
  is a complete rewrite based on the c++ db/db_bench.cc and the
  DbBenchmark in dain's java leveldb.
* Support multithreading.
* 'readseq' is currently not supported as it requires RocksDB Iterator.

* usage:

  --benchmarks
    Comma-separated list of operations to run in the specified order
        Actual benchmarks:
                fillseq    -- write N values in sequential key order in async mode
                fillrandom -- write N values in random key order in async mode
                fillbatch  -- write N/1000 batch where each batch has 1000 values
                              in random key order in sync mode
                fillsync   -- write N/100 values in random key order in sync mode
                fill100K   -- write N/1000 100K values in random order in async mode
                readseq    -- read N times sequentially
                readrandom -- read N times in random order
                readhot    -- read N times in random order from 1% section of DB
        Meta Operations:
                delete     -- delete DB
    DEFAULT: [fillseq, readrandom, fillrandom]

  --compression_ratio
    Arrange to generate values that shrink to this fraction of
        their original size after compression
    DEFAULT: 0.5

  --use_existing_db
    If true, do not destroy the existing database.  If you set this
        flag and also specify a benchmark that wants a fresh database,  that benchmark will fail.
    DEFAULT: false

  --num
    Number of key/values to place in database.
    DEFAULT: 1000000

  --threads
    Number of concurrent threads to run.
    DEFAULT: 1

  --reads
    Number of read operations to do.  If negative, do --nums reads.

  --key_size
    The size of each key in bytes.
    DEFAULT: 16

  --value_size
    The size of each value in bytes.
    DEFAULT: 100

  --write_buffer_size
    Number of bytes to buffer in memtable before compacting
        (initialized to default value by 'main'.)
    DEFAULT: 4194304

  --cache_size
    Number of bytes to use as a cache of uncompressed data.
        Negative means use default settings.
    DEFAULT: -1

  --seed
    Seed base for random number generators.
    DEFAULT: 0

  --db
    Use the db with the following name.
    DEFAULT: /tmp/rocksdbjni-bench

* Add RocksDB.write().

Test Plan: make jbench

Reviewers: haobo, sdong, dhruba, ankgup87

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17433

Summary:
GetProperty test is flakey.
Before this diff: P8635927
After: P8635945

We need to make sure the thread is done before we destruct sleeping tasks. Otherwise, bad things happen.

Test Plan: See summary

Reviewers: ljin, sdong, haobo, dhruba

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17595

[JNI] Add JNI bindings for rocksdb Options

Summary: env_ is not used. Compiling for iOS complains.

Test Plan: compiles now

Reviewers: ljin, haobo, sdong, dhruba

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17589

Summary:
clean up the db_bench a little bit. also avoid allocating memory for key
in the loop

Test Plan:
I verified a run with filluniquerandom & readrandom. Iterator seek will be used lot
to measure performance. Will fix whatever comes up

Reviewers: haobo, igor, yhchiang

Reviewed By: igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17559

Summary: ToString() is expensive. Profiling shows that most compaction threads are stuck in jemalloc, allocating a new string. This will help out a litte.

Test Plan: make check

Reviewers: haobo, danguo

Reviewed By: danguo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17583

Summary: This will allow us to disable them completely for iOS or for better performance

Test Plan: will run make all check

Reviewers: igor, haobo, dhruba

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17511

Summary:
Fixed the following column family related compile error.

./java/rocksjni/write_batch.cc:211:66: error: cannot initialize a parameter of type 'rocksdb::ColumnFamilyMemTables *' with an lvalue of type 'rocksdb::MemTable *'
  rocksdb::Status s = rocksdb::WriteBatchInternal::InsertInto(b, mem, &options);
                                                                   ^~~

Test Plan:
make jni
make jtest

Reviewers: igor, haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17577

Summary:
Move PlainTableIterator's copied key from std::string local buffer to avoid paying the extra costs in std::string related to sharing. Reuse the same buffer class in DbIter. Move the class to dbformat.h.

This patch improves iterator performance significantly. Running this benchmark:

./table_reader_bench --num_keys2=17 --iterator --plain_table --time_unit=nanosecond

The average latency is improved to about 750 nanoseconds from 1100 nanoseconds.

Test Plan:
Add a unit test.
make all check

Reviewers: haobo, ljin

Reviewed By: haobo

CC: igor, yhchiang, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D17547

Summary: I think this issue was caused by bad merge. We have to initialize bloom_locality, otherwise valgrind complains: "Use of uninitialised value of size 8"

Test Plan: Run valgrind ./prefix_test

Reviewers: ljin

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17553

This will enable user to use only 1 background thread.

Conflicts:
	db/db_impl.cc
	db/db_impl.h
	db/memtable_list.cc
	db/version_set.cc

Summary: If a client specifies wal_dir with trailing '/', we will fail in deleting obsolete log files. See task #4083746

Test Plan: make check

Reviewers: haobo, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17535

Expose JNI layer for these options: block_size, max_write_buffer_number, write_buffer_size, disable_seek_compaction, max_background_compactions.

Summary: Update HISTORY.md to make existing items to 2.8 release and add something I think is missing.

Test Plan: N/A

Reviewers: haobo, igor, ljin, dhruba, yhchiang, xjin

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17517

Summary: Our measurement shows that sometimes new log::Write's constructor can take hundreds of milliseconds. It's unclear why but just simply move it out of DB mutex.

Test Plan: make all check

Reviewers: haobo, ljin, igor

Reviewed By: haobo

CC: nkg-, yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D17487

Summary: per sdong's request, this will help processor prefetch on n->key case.

Test Plan: make all check

Reviewers: sdong, haobo, igor

Reviewed By: sdong

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17415

Summary: Otherwise, if we compile on machine with SSE4.2 support and run it on machine without the support, we will fail.

Test Plan: compiles, verified that isSse42() gets called.

Reviewers: dhruba

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17505

Summary:
I had to make number of changes to the code and Makefile:
* Add `make lib`, that will create static library without debug info. We need this to avoid growing binary too much. Currently it's 14MB.
* Remove cpuinfo() function and use __SSE4_2__ macro. We actually used the macro as part of Fast_CRC32() function.
As a result, I also accidentally fixed this issue: https://www.facebook.com/groups/rocksdb.dev/permalink/549700778461774/?stream_ref=2
* Remove __thread locals in OS_MACOSX

Test Plan: `make lib PLATFORM=IOS`

Reviewers: ljin, haobo, dhruba, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17475

Summary: Flushing log buffer earlier to avoid confusion of time holding the locks.

Test Plan: Should be safe as long as several related db test passes

Reviewers: haobo, igor, ljin

Reviewed By: igor

CC: nkg-, leveldb

Differential Revision: https://reviews.facebook.net/D17493

Summary: Fix some signed and unsigned comparisons to make some other build script happy.

Test Plan: Build and run those changed tests

Reviewers: ljin, igor, haobo

Reviewed By: igor

CC: yhchiang, dhruba, kailiu, leveldb

Differential Revision: https://reviews.facebook.net/D17463

Summary: as title, make it easy to turn on/off profiling at per thread level.

Test Plan: make check

Reviewers: sdong, ljin

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17469