Summary:
= Major Changes =
* Add a new mem-table representation, HashCuckooRep, which is based cuckoo hash.
  Cuckoo hash uses multiple hash functions.  This allows each key to have multiple
  possible locations in the mem-table.

  - Put: When insert a key, it will try to find whether one of its possible
    locations is vacant and store the key.  If none of its possible
    locations are available, then it will kick out a victim key and
    store at that location.  The kicked-out victim key will then be
    stored at a vacant space of its possible locations or kick-out
    another victim.  In this diff, the kick-out path (known as
    cuckoo-path) is found using BFS, which guarantees to be the shortest.

 - Get: Simply tries all possible locations of a key --- this guarantees
   worst-case constant time complexity.

 - Time complexity: O(1) for Get, and average O(1) for Put if the
   fullness of the mem-table is below 80%.

 - Default using two hash functions, the number of hash functions used
   by the cuckoo-hash may dynamically increase if it fails to find a
   short-enough kick-out path.

 - Currently, HashCuckooRep does not support iteration and snapshots,
   as our current main purpose of this is to optimize point access.

= Minor Changes =
* Add IsSnapshotSupported() to DB to indicate whether the current DB
  supports snapshots.  If it returns false, then DB::GetSnapshot() will
  always return nullptr.

Test Plan:
Run existing tests.  Will develop a test specifically for cuckoo hash in
the next diff.

Reviewers: sdong, haobo

Reviewed By: sdong

CC: leveldb, dhruba, igor

Differential Revision: https://reviews.facebook.net/D16155

Summary:
ReadFirstRecord() reads the actual log file from disk on every call. This diff introduces a cache layer on top of ReadFirstRecord(), which should significantly speed up repeated calls to GetUpdatesSince().

I also cleaned up some stuff, but the whole TransactionLogIterator could use some refactoring, especially if we see increased usage.

Test Plan: make check

Reviewers: haobo, sdong, dhruba

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18387

Summary:
This enables user to add a TTL column family to normal DB.

Next step should be to expand StackableDB and create StackableColumnFamily, such that users can for example add geo-spatial column families to normal DB.

Test Plan: added a test

Reviewers: dhruba, haobo, ljin

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18201

Summary:
When TransactionLogIterator comes to EOF, it calls UnmarkEOF and continues reading. However, if glibc cached the EOF status of the file, it will get EOF again, even though the new data might have been written to it.

This has been causing errors in Mac OS.

Test Plan: test passes, was failing before

Reviewers: dhruba, haobo, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18381

[Java] Fixed compile error due to the removal of ReadOptions.prefix_seek, minor improvement on DbBenchmark.java.

Add rocksdb_open_for_read_only to C API

Summary: Read-only BackupEngine can connect to the same backup directory that is already running BackupEngine. That enables some interesting use-cases (i.e. restoring replica from primary's backup directory)

Test Plan: added a unit test

Reviewers: dhruba, haobo, ljin

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18297

Summary:
this is to reclaim the regression introduced in
https://reviews.facebook.net/D17853

Test Plan: make all check

Reviewers: igor, haobo, sdong, dhruba, yhchiang

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17985

Summary:
As a follow-up diff for https://reviews.facebook.net/D17805, add
optimization to check PrefixMayMatch on Seek()

Test Plan: make all check

Reviewers: igor, haobo, sdong, yhchiang, dhruba

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17853

Summary:
also add an override option total_order_iteration if you want to use full
iterator with prefix_extractor

Test Plan: make all check

Reviewers: igor, haobo, sdong, yhchiang

Reviewed By: haobo

CC: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D17805

Summary: As summary. Add two autovectors that get filled up in MakeRoomForWrite and they get deleted outside of mutex

Test Plan: make check

Reviewers: dhruba, haobo, ljin, sdong

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18249

Summary:
Now that we have column families involved, we need to add extra context to every log message. They now start with "[column family name] log message"

Also added some logging that I think would be useful, like level summary after every flush (I often needed that when going through the logs).

Test Plan: make check + ran db_bench to confirm I'm happy with log output

Reviewers: dhruba, haobo, ljin, yhchiang, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18303

Summary:
Now this gives us the real deal stack trace:

    Assertion failed: (false), function GetProperty, file db/db_impl.cc, line 4072.
    Received signal 6 (Abort trap: 6)
    #0   0x7fff57ce39b9
    #1   abort (in libsystem_c.dylib) + 125
    #2   basename (in libsystem_c.dylib) + 0
    #3   rocksdb::DBImpl::GetProperty(rocksdb::ColumnFamilyHandle*, rocksdb::Slice const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*) (in db_test) (db_impl.cc:4072)
    #4   rocksdb::_Test_Empty::_Run() (in db_test) (testharness.h:68)
    #5   rocksdb::_Test_Empty::_RunIt() (in db_test) (db_test.cc:1005)
    #6   rocksdb::test::RunAllTests() (in db_test) (testharness.cc:60)
    #7   main (in db_test) (db_test.cc:6697)
    #8   start (in libdyld.dylib) + 1

Test Plan: added artificial assert, saw great stack trace

Reviewers: haobo, dhruba, ljin

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18309

[Java] Enable filluniquerandom, readseq, BloomFilter, and 70+ command-line options to DbBenchmark.java

Summary:
* Add filluniquerandom
* Add readseq, implemented using iterator.
* Realize most command-line-arguments from db_bench.cc (70+).
* Some code are commented out as some of the options in Options
  not yet have Java bindings.
* Add default option to DbBenchmark.
* RocksDB will now take the ownership of all c++ raw-pointers from Options, which includes a c++ raw-pointer for Filter.

Test Plan: ./jdb_bench.sh --db=/tmp/rocksjava-bench/db --num_levels=6 --key_size=20 --prefix_size=20 --keys_per_prefix=0 --value_size=100 --block_size=4096 --cache_size=17179869184 --cache_numshardbits=6 --compression_ratio=1 --min_level_to_compress=-1 --disable_seek_compaction=1 --hard_rate_limit=2 --write_buffer_size=134217728 --max_write_buffer_number=2 --level0_file_num_compaction_trigger=8 --target_file_size_base=134217728 --max_bytes_for_level_base=1073741824 --disable_wal=0 --wal_dir=/tmp/rocksjava-bench/wal --sync=0 --disable_data_sync=1 --verify_checksum=1 --delete_obsolete_files_period_micros=314572800 --max_grandparent_overlap_factor=10 --max_background_compactions=4 --max_background_flushes=0 --level0_slowdown_writes_trigger=16 --level0_stop_writes_trigger=24 --statistics=0 --stats_per_interval=0 --stats_interval=1048576 --histogram=0 --use_plain_table=1 --open_files=-1 --mmap_read=1 --mmap_write=0 --memtablerep=prefix_hash --bloom_bits=10 --bloom_locality=1 --perf_level=0 --benchmarks=filluniquerandom,readseq,readrandom --use_existing_db=0 --threads=4

Reviewers: haobo, dhruba, sdong, ankgup87, rsumbaly, swapnilghike, zzbennett

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18267

Summary:
I'm getting lots of e-mails with CompactionInputErrorParanoid failing. Most recent example early morning today was: http://ci-builds.fb.com/job/rocksdb_valgrind/562/consoleFull

I'm putting a stop to these e-mails. I investigated why the test is flakey and it turns out it's because of non-determinsim of compaction scheduling. If there is a compaction after the last flush, CorruptFile will corrupt the compacted file instead of file at level 0 (as it assumes). That makes `Check(9, 9)` fail big time.

I also saw some errors with table file getting outputed to >= 1 levels instead of 0. Also fixed that.

Test Plan: Ran corruption_test 100 times without a failure. Previously it usually failed at 10th occurrence.

Reviewers: dhruba, haobo, ljin

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18285

Summary: Sometimes, our tests fail because of normal `assert` call. It would be helpful to see stack trace in that case, too.

Test Plan: Added `assert(false)` and verified it prints out stack trace

Reviewers: haobo, dhruba, sdong, ljin, yhchiang

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18291

Summary:
Currently, whenever DB Verification fails we bail out by calling `exit(1)`. This is kind of bad since it causes unclean shutdown and spew of error log messages like:

    05:03:27 pthread lock: Invalid argument
    05:03:27 pthread lock: Invalid argument
    05:03:27 pthread lock: Invalid argument
    05:03:27 pthread lock: Invalid argument
    05:03:27 pthread lock: Invalid argument
    05:03:27 pthread lock: Invalid argument
    05:03:27 pthread lock: Invalid argument
    05:03:27 pthread lock: Invalid argument
    05:03:27 pthread lock: Invalid argument

This diff adds a new parameter that is set to true when verification fails. It can then use the parameter to bail out safely.

Test Plan: Casued artificail failure. Verified that exit was clean.

Reviewers: dhruba, haobo, ljin

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18243

Summary:
Add Java bindings and Java tests for 30+ rocksdb::Options.  Codes are
machine-genearted based on include/rocksdb/options.h with manual-polishment.

Test Plan:
make rocksdbjava
make jtest

Reviewers: haobo, dhruba, sdong, ankgup87, rsumbaly, swapnilghike, zzbennett

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18273

Summary: IterKey set buffer_size_ to a wrong initial value, causing it to always allocate values from heap instead of stack if the key size is smaller. Fix it.

Test Plan: make all check

Reviewers: haobo, ljin

Reviewed By: haobo

CC: igor, dhruba, yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D18279

Summary: While debugging Mac-only issue with ThreadLocalPtr, this was very useful. Let's print out stack trace in MAC OS, too.

Test Plan: Verified that somewhat useful stack trace was generated on mac. Will run PrintStack() on linux, too.

Reviewers: ljin, haobo

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18189

Summary: In this patch, two new DB properties are defined: rocksdb.num-immutable-mem-table and rocksdb.num-entries-imm-mem-tables, from where number of entries in mem tables can be exposed to users

Test Plan:
Cover the codes in db_test
make all check

Reviewers: haobo, ljin, igor

Reviewed By: igor

CC: nkg-, igor, yhchiang, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D18207

Summary: Get rid of the devil. Probably won't impact anything on the perf side.

Test Plan: make all check

Reviewers: igor, haobo, sdong, yhchiang

Reviewed By: haobo

CC: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D18153

Summary:
make singleton a static member instead of dynamic object. This should
also avoid the race on unique_ptr

Test Plan: make all check

Reviewers: igor, haobo, sdong

Reviewed By: igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18177