Summary: DBTestXactLogIterator.TransactionLogIterator was failing due the sequence gaps. This was caused by an off-by-one error when calculating the new sequence number after recovering from logs.

Test Plan: db_log_iter_test

Reviewers: andrewkr

Subscribers: andrewkr, hermanlee4, dhruba, IslamAbdelRahman

Differential Revision: https://reviews.facebook.net/D58053

Summary: Store SST file compression algorithm as a TableProperty.

Test Plan: Modified and ran the table_test UT that checks for TableProperties

Reviewers: IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: lgalanis, andrewkr, dhruba, IslamAbdelRahman

Differential Revision: https://reviews.facebook.net/D58017

Summary:
The implementation remains where it is. Only the
header is exported. This is so that a customized
ldb tool can print help along with its own
extra commands

Test Plan: make ldb

Reviewers: sdong, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D57255

Summary: Disable backupable_db_test.cc on Windows since EnvChroot is not supported

Test Plan: check ROCKSDB_LITE

Reviewers: andrewkr

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D58035

Summary:
- Used ChrootEnv so the database and backup Envs are isolated in the filesystem.
- Removed DifferentEnvs test since now every test uses different Envs

Depends on D57543

Test Plan:
- ran backupable_db_test
- verified backupable_db_test now catches the bug when D57159 is backed out (this bug previously passed through the test cases, which motivated this change)

Reviewers: sdong, lightmark, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57615

Summary:
GetObsoleteFiles() and LogAndApply() functions modify obsolete_manifests_ vector
we need to make sure that the mutex is held when we modify the obsolete_manifests_

Test Plan: run the test under TSAN

Reviewers: andrewkr

Reviewed By: andrewkr

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D58011

Summary:
Expose the option so it's easy to run offline tests of compression
dictionary feature.

Test Plan:
verified compression dictionary is loaded into lz4 for below command:

  $ ./ldb compact --compression_type=lz4 --compression_max_dict_bytes=16384 --db=/tmp/feed-compression-test/

Reviewers: IslamAbdelRahman, sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57441

Summary:
1. prepare()
2. crash
3. recover
4. commit()
5. crash
6. data is lost

This is due to the transaction data still only residing in the WAL but because the logs were flushed on the first recovery the data is ignored on the second recovery. We must scan all logs found on recovery and only ignore redundant data at the time of replay. It is not possible to know which logs still contain relevant data at time of recovery. We cannot simply ignore a log because all of the non-2pc data it contains has already been written to L0.

The changes made to MemTableInserter are to ensure that prepared sections are still recovered even if all of the non-2pc data in that log has already been flushed to L0.

Test Plan: Provided test.

Reviewers: sdong

Subscribers: andrewkr, hermanlee4, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57729

Summary:
Consider the following WAL with 4 batch entries prefixed with their sequence at time of memtable insert.
[1: BEGIN_PREPARE, PUT, PUT, PUT, PUT, END_PREPARE(a)]
[1: BEGIN_PREPARE, PUT, PUT, PUT, PUT, END_PREPARE(b)]
[4: COMMIT(a)]
[7: COMMIT(b)]

The first two batches do not consume any sequence numbers so are both prefixed with seq=1.
For 2pc commit, memtable insertion takes place before COMMIT batch is written to WAL.
We can see that sequence number consumption takes place between WAL entries giving us the seemingly sparse sequence prefix for WAL entries.
This is a valid WAL.

Because with 2PC markers one WriteBatch points to another batch containing its inserts a writebatch can consume more or less sequence numbers than the number of sequence consuming entries that it contains.

We can see that, given the entries in the WAL, 6 sequence ids were consumed. Yet on recovery the maximum sequence consumed would be 7 + 3 (the number of sequence numbers consumed by COMMIT(b))

So, now upon recovery we must track the actual consumption of sequence numbers.
In the provided scenario there will be no sequence gaps, but it is possible to produce a sequence gap. This should not be a problem though. correct?

Test Plan: provided test.

Reviewers: sdong

Subscribers: andrewkr, leveldb, dhruba, hermanlee4

Differential Revision: https://reviews.facebook.net/D57645

Summary:
Two Phase Commit addition to RocksDB.

See wiki: https://github.com/facebook/rocksdb/wiki/Two-Phase-Commit-Implementation
Quip: https://fb.quip.com/pxZrAyrx53r3

Depends on:
WriteBatch modification: https://reviews.facebook.net/D54093
Memtable Log Referencing and Prepared Batch Recovery: https://reviews.facebook.net/D56919

Test Plan:
- SimpleTwoPhaseTransactionTest
- PersistentTwoPhaseTransactionTest.
- TwoPhaseRollbackTest
- TwoPhaseMultiThreadTest
- TwoPhaseLogRollingTest
- TwoPhaseEmptyWriteTest
- TwoPhaseExpirationTest

Reviewers: IslamAbdelRahman, sdong

Reviewed By: sdong

Subscribers: leveldb, hermanlee4, andrewkr, vasilep, dhruba, santoshb

Differential Revision: https://reviews.facebook.net/D56925

Summary:
This diff is built on top of WriteBatch modification: https://reviews.facebook.net/D54093 and adds the required functionality to rocksdb core necessary for rocksdb to support 2PC.

modfication of DBImpl::WriteImpl()
- added two arguments *uint64_t log_used = nullptr, uint64_t log_ref = 0;
- *log_used is an output argument which will return the log number which the incoming batch was inserted into, 0 if no WAL insert took place.
-  log_ref is a supplied log_number which all memtables inserted into will reference after the batch insert takes place. This number will reside in 'FindMinPrepLogReferencedByMemTable()' until all Memtables insertinto have flushed.

- Recovery/writepath is now aware of prepared batches and commit and rollback markers.

Test Plan: There is currently no test on this diff. All testing of this functionality takes place in the Transaction layer/diff but I will add some testing.

Reviewers: IslamAbdelRahman, sdong

Subscribers: leveldb, santoshb, andrewkr, vasilep, dhruba, hermanlee4

Differential Revision: https://reviews.facebook.net/D56919

Summary: Adds three new WriteBatch data types: Prepare(xid), Commit(xid), Rollback(xid). Prepare(xid) should precede the (single) operation to which is applies. There can obviously be multiple Prepare(xid) markers. There should only be one Rollback(xid) or Commit(xid) marker yet not both. None of this logic is currently enforced and will most likely be implemented further up such as in the memtableinserter. All three markers are similar to PutLogData in that they are writebatch meta-data, ie stored but not counted. All three markers differ from PutLogData in that they will actually be written to disk. As for WriteBatchWithIndex, Prepare, Commit, Rollback are all implemented just as PutLogData and none are tested just as PutLogData.

Test Plan: single unit test in write_batch_test.

Reviewers: hermanlee4, sdong, anthony

Subscribers: leveldb, dhruba, vasilep, andrewkr

Differential Revision: https://reviews.facebook.net/D57867

Summary:
On Mac OS X, the chroot directory we typically use ("/tmp") is actually
a symlink for "/private/tmp". Since we dereference symlinks in user-defined
paths, we must also dereference symlinks in chroot_dir_ such that we can perform
string comparisons on those paths.

Test Plan: ran env_test on Mac OS X and devserver

Reviewers: sdong, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57957

Summary: Fix lite build

Test Plan: run under lite

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D57945

Summary:
Add a new option that can be used to set a specific compression algorithm for bottommost level.
This option will only affect levels larger than base level.

I have also updated CompactionJobInfo to include the compression algorithm used in compaction

Test Plan:
added new unittest
existing unittests

Reviewers: andrewkr, yhchiang, sdong

Reviewed By: sdong

Subscribers: lightmark, andrewkr, dhruba, yoshinorim

Differential Revision: https://reviews.facebook.net/D57669

Summary: Currently we estimate bytes needed for compaction by assuming fanout value to be level multiplier. It overestimates when size of a level exceeds the target by large. We estimate by the ratio of actual sizes in levels instead.

Test Plan: Fix existing test cases and add a new one.

Reviewers: IslamAbdelRahman, igor, yhchiang

Reviewed By: yhchiang

Subscribers: MarkCallaghan, leveldb, andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D57789

Summary: see title

Test Plan:
  $ /mnt/gvfs/third-party2/valgrind/af85c56f424cd5edfc2c97588299b44ecdec96bb/3.10.0/gcc-4.9-glibc-2.20/e9936bf/bin/valgrind --error-exitcode=2 --leak-check=full ./env_test

Reviewers: IslamAbdelRahman, sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57897

Summary:
This diff includes an initial script running a set of benchmarks for
regression test.  The script does the following things:

  checkout the specified rocksdb commit (or origin/master as default)
  make clean && DEBUG_LEVEL=0 make db_bench
  setup test directories
  run set of benchmarks and store results

Currently, the script will run couple benchmarks, store all the benchmark
output, extract micros per op and percentile information for each benchmark
and store them in a single SUMMARY.csv file.  The SUMMARY.csv will make the
follow-up regression detection easier.

In addition, the current script only takes env arguments to set important
attributes of db_bench.  Will follow-up with a patch that allows db_bench
to construct options from an options file.

Test Plan:
NUM_KEYS=100 ./tools/regression_test.sh

  Sample SUMMARY.csv file:

                                     commit id,                      benchmark,  ms-per-op,        p50,        p75,        p99,      p99.9,     p99.99
      7e23ddf575890510e7d2fc7a79b31a1bbf317917,                        fillseq,      15.28,      54.66,      77.14,    5000.00,   17900.00,   18483.00
      7e23ddf575890510e7d2fc7a79b31a1bbf317917,                      overwrite,      13.54,      57.69,      86.39,    3000.00,   15600.00,   17013.00
      7e23ddf575890510e7d2fc7a79b31a1bbf317917,                     readrandom,       1.04,       0.80,       1.67,     293.33,     395.00,     504.00
      7e23ddf575890510e7d2fc7a79b31a1bbf317917,               readwhilewriting,       2.75,       1.01,       1.87,     200.00,     460.00,     485.00
      7e23ddf575890510e7d2fc7a79b31a1bbf317917,                   deleterandom,       3.64,      48.12,      70.09,     200.00,     336.67,     347.00
      7e23ddf575890510e7d2fc7a79b31a1bbf317917,                     seekrandom,      24.31,     391.87,     513.69,     872.73,     990.00,    1048.00
      7e23ddf575890510e7d2fc7a79b31a1bbf317917,         seekrandomwhilewriting,      14.02,     185.14,     294.15,     700.00,    1440.00,    1527.00

Reviewers: sdong, IslamAbdelRahman, kradhakrishnan, yiwu, andrewkr, gunnarku

Reviewed By: gunnarku

Subscribers: gunnarku, MarkCallaghan, andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57597

Summary:
Pass --index_block_restart_interval flag to block_based_options in db_bench tool.

Test Plan: none

Reviewers: sdong, kradhakrishnan

Reviewed By: kradhakrishnan

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D57699

Summary: Fixing error with win build where we compare int64_t with size_t.

Test Plan: make check

Reviewers: andrewkr

Reviewed By: andrewkr

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57885

Summary:
Fix below error:

  use of undeclared identifier 'errno'

Test Plan: doitlive

Reviewers: IslamAbdelRahman, sdong

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57849

Summary:
For testing backups, we needed an Env that is fully isolated from other
Envs on the same machine. Our in-memory Envs (MockEnv and InMemoryEnv) were
insufficient because they don't implement most directory operations.

This diff introduces a new Env, "ChrootEnv", that translates paths such that the
chroot directory appears to be the root directory. This way, multiple Envs can
be isolated in the filesystem by using different chroot directories. Since we
use the filesystem, all directory operations are trivially supported.

Test Plan:
I parameterized the existing EnvPosixTest so it runs tests on ChrootEnv
except the ioctl-related cases.

Reviewers: sdong, lightmark, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57543

Summary: Revert D54093 and D57453

Test Plan: running make check

Reviewers: horuff, sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57819

Summary:
This is needed so that rocksdb users can add more
commands to the included ldb tool by adding more custom
commands.

Test Plan: make -j ldb

Reviewers: sdong, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D57243

Closes https://github.com/facebook/rocksdb/issues/1071

Summary: Have sandcastle run unit test in lite mode for every diff.

Test Plan: seems sandcastle picked up changes here and running lite_test for this diff.

Reviewers: kradhakrishnan

Reviewed By: kradhakrishnan

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57741

Summary:
For backwards compatibility with older option strings, the parser needs
to treat this argument as optional.

Test Plan:
Updated unit test to cover case where compression_opts is present but
max_dict_bytes is omitted.

Reviewers: MarkCallaghan, sdong, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57759

Summary: This is to provide a way for users to skip prefix bloom in point look-up.

Test Plan: Add a new unit test scenario.

Reviewers: IslamAbdelRahman

Subscribers: leveldb, andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D57747

Summary: We changed default options of max_open_files and max_file_opening_threads but didn't revert it in OptimizeForSmallDb().

Test Plan: Add a unit test

Reviewers: igor, yhchiang, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: leveldb, andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D57675

Summary: This test is failing under valgrind because we dont delete the Env that we allocated

Test Plan: run the test under valgrind

Reviewers: andrewkr, yhchiang, yiwu, sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D57693

Summary:
Add optimize_filters_for_hits option to db_bench

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: sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D57621

Summary: Fixing lite build broke in unit test. `FilesPerLevel()` depends on `DB::GetProperty()`, which lite build doesn't support.

Test Plan: OPT=-DROCKSDB_LITE make check -j64

Reviewers: sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57651

Summary:
Add an option `iterator_readahead_size` to `ReadOptions` to enable
configurable readahead for iterators similar to the corresponding
option for compaction.

Test Plan:
```
make commit_prereq
```

Reviewers: kumar.rangarajan, ott, igor, sdong

Reviewed By: sdong

Subscribers: yiwu, andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D55419

Summary: We should not use IterKey::SetKey with copy = false except if we are pinning the iterator thru it's life time, otherwise we may release the temporarily pinned blocks and in this case the IterKey will be pointing to freed memory

Test Plan: added a new test

Reviewers: sdong, andrewkr

Reviewed By: andrewkr

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D57561

Summary:
This diff is stacked on top of this diff https://reviews.facebook.net/D56493
The current Iterator::Prev() implementation need to copy every value since the underlying Iterator may move after reading the value.
This can be optimized by making sure that the block containing the value is pinned until the Iterator move. which will improve the throughput by up to 1.5X

master
```
==> 1000000_Keys_100Byte.txt <==
readreverse  :       0.449 micros/op 2225887 ops/sec;  246.2 MB/s
readreverse  :       0.433 micros/op 2311508 ops/sec;  255.7 MB/s
readreverse  :       0.436 micros/op 2294335 ops/sec;  253.8 MB/s
readreverse  :       0.471 micros/op 2121295 ops/sec;  234.7 MB/s
readreverse  :       0.465 micros/op 2152227 ops/sec;  238.1 MB/s
readreverse  :       0.454 micros/op 2203011 ops/sec;  243.7 MB/s
readreverse  :       0.451 micros/op 2216095 ops/sec;  245.2 MB/s
readreverse  :       0.462 micros/op 2162447 ops/sec;  239.2 MB/s
readreverse  :       0.476 micros/op 2099151 ops/sec;  232.2 MB/s
readreverse  :       0.472 micros/op 2120710 ops/sec;  234.6 MB/s

avg : 242.34 MB/s

==> 1000000_Keys_1KB.txt <==
readreverse  :       1.013 micros/op 986793 ops/sec;  978.7 MB/s
readreverse  :       0.942 micros/op 1061136 ops/sec; 1052.5 MB/s
readreverse  :       0.951 micros/op 1051901 ops/sec; 1043.3 MB/s
readreverse  :       0.932 micros/op 1072894 ops/sec; 1064.1 MB/s
readreverse  :       1.024 micros/op 976720 ops/sec;  968.7 MB/s
readreverse  :       0.935 micros/op 1069169 ops/sec; 1060.4 MB/s
readreverse  :       1.012 micros/op 988132 ops/sec;  980.1 MB/s
readreverse  :       0.962 micros/op 1039579 ops/sec; 1031.1 MB/s
readreverse  :       0.991 micros/op 1008924 ops/sec; 1000.7 MB/s
readreverse  :       1.004 micros/op 996144 ops/sec;  988.0 MB/s

avg : 1016.76 MB/s

==> 1000000_Keys_10KB.txt <==
readreverse  :       4.167 micros/op 239952 ops/sec; 2346.9 MB/s
readreverse  :       4.070 micros/op 245713 ops/sec; 2403.3 MB/s
readreverse  :       4.572 micros/op 218733 ops/sec; 2139.4 MB/s
readreverse  :       4.497 micros/op 222388 ops/sec; 2175.2 MB/s
readreverse  :       4.203 micros/op 237920 ops/sec; 2327.1 MB/s
readreverse  :       4.206 micros/op 237756 ops/sec; 2325.5 MB/s
readreverse  :       4.181 micros/op 239149 ops/sec; 2339.1 MB/s
readreverse  :       4.157 micros/op 240552 ops/sec; 2352.8 MB/s
readreverse  :       4.187 micros/op 238848 ops/sec; 2336.1 MB/s
readreverse  :       4.106 micros/op 243575 ops/sec; 2382.4 MB/s

avg : 2312.78 MB/s

==> 100000_Keys_100KB.txt <==
readreverse  :      41.281 micros/op 24224 ops/sec; 2366.0 MB/s
readreverse  :      39.722 micros/op 25175 ops/sec; 2458.9 MB/s
readreverse  :      40.319 micros/op 24802 ops/sec; 2422.5 MB/s
readreverse  :      39.762 micros/op 25149 ops/sec; 2456.4 MB/s
readreverse  :      40.916 micros/op 24440 ops/sec; 2387.1 MB/s
readreverse  :      41.188 micros/op 24278 ops/sec; 2371.4 MB/s
readreverse  :      40.061 micros/op 24962 ops/sec; 2438.1 MB/s
readreverse  :      40.221 micros/op 24862 ops/sec; 2428.4 MB/s
readreverse  :      40.084 micros/op 24947 ops/sec; 2436.7 MB/s
readreverse  :      40.655 micros/op 24597 ops/sec; 2402.4 MB/s

avg : 2416.79 MB/s

==> 10000_Keys_1MB.txt <==
readreverse  :     298.038 micros/op 3355 ops/sec; 3355.3 MB/s
readreverse  :     335.001 micros/op 2985 ops/sec; 2985.1 MB/s
readreverse  :     286.956 micros/op 3484 ops/sec; 3484.9 MB/s
readreverse  :     329.954 micros/op 3030 ops/sec; 3030.8 MB/s
readreverse  :     306.428 micros/op 3263 ops/sec; 3263.5 MB/s
readreverse  :     330.749 micros/op 3023 ops/sec; 3023.5 MB/s
readreverse  :     328.903 micros/op 3040 ops/sec; 3040.5 MB/s
readreverse  :     324.853 micros/op 3078 ops/sec; 3078.4 MB/s
readreverse  :     320.488 micros/op 3120 ops/sec; 3120.3 MB/s
readreverse  :     320.536 micros/op 3119 ops/sec; 3119.8 MB/s

avg : 3150.21 MB/s
```

After memcpy elimination
```

==> 1000000_Keys_100Byte.txt <==
readreverse  :       0.395 micros/op 2529890 ops/sec;  279.9 MB/s
readreverse  :       0.368 micros/op 2715922 ops/sec;  300.5 MB/s
readreverse  :       0.384 micros/op 2603929 ops/sec;  288.1 MB/s
readreverse  :       0.375 micros/op 2663286 ops/sec;  294.6 MB/s
readreverse  :       0.357 micros/op 2802180 ops/sec;  310.0 MB/s
readreverse  :       0.363 micros/op 2757684 ops/sec;  305.1 MB/s
readreverse  :       0.372 micros/op 2689603 ops/sec;  297.5 MB/s
readreverse  :       0.379 micros/op 2638599 ops/sec;  291.9 MB/s
readreverse  :       0.375 micros/op 2663803 ops/sec;  294.7 MB/s
readreverse  :       0.375 micros/op 2665579 ops/sec;  294.9 MB/s

avg: 295.72 MB/s (1.22 X)

==> 1000000_Keys_1KB.txt <==
readreverse  :       0.879 micros/op 1138112 ops/sec; 1128.8 MB/s
readreverse  :       0.842 micros/op 1187998 ops/sec; 1178.3 MB/s
readreverse  :       0.837 micros/op 1194915 ops/sec; 1185.1 MB/s
readreverse  :       0.845 micros/op 1182983 ops/sec; 1173.3 MB/s
readreverse  :       0.877 micros/op 1140308 ops/sec; 1131.0 MB/s
readreverse  :       0.849 micros/op 1177581 ops/sec; 1168.0 MB/s
readreverse  :       0.915 micros/op 1093284 ops/sec; 1084.3 MB/s
readreverse  :       0.863 micros/op 1159418 ops/sec; 1149.9 MB/s
readreverse  :       0.895 micros/op 1117670 ops/sec; 1108.5 MB/s
readreverse  :       0.852 micros/op 1174116 ops/sec; 1164.5 MB/s

avg: 1147.17 MB/s (1.12 X)

==> 1000000_Keys_10KB.txt <==
readreverse  :       3.870 micros/op 258386 ops/sec; 2527.2 MB/s
readreverse  :       3.568 micros/op 280296 ops/sec; 2741.5 MB/s
readreverse  :       4.005 micros/op 249694 ops/sec; 2442.2 MB/s
readreverse  :       3.550 micros/op 281719 ops/sec; 2755.5 MB/s
readreverse  :       3.562 micros/op 280758 ops/sec; 2746.1 MB/s
readreverse  :       3.507 micros/op 285125 ops/sec; 2788.8 MB/s
readreverse  :       3.463 micros/op 288739 ops/sec; 2824.1 MB/s
readreverse  :       3.428 micros/op 291734 ops/sec; 2853.4 MB/s
readreverse  :       3.553 micros/op 281491 ops/sec; 2753.2 MB/s
readreverse  :       3.535 micros/op 282885 ops/sec; 2766.9 MB/s

avg : 2719.89 MB/s (1.17 X)

==> 100000_Keys_100KB.txt <==
readreverse  :      22.815 micros/op 43830 ops/sec; 4281.0 MB/s
readreverse  :      29.957 micros/op 33381 ops/sec; 3260.4 MB/s
readreverse  :      25.334 micros/op 39473 ops/sec; 3855.4 MB/s
readreverse  :      23.037 micros/op 43409 ops/sec; 4239.8 MB/s
readreverse  :      27.810 micros/op 35958 ops/sec; 3512.1 MB/s
readreverse  :      30.327 micros/op 32973 ops/sec; 3220.6 MB/s
readreverse  :      29.704 micros/op 33665 ops/sec; 3288.2 MB/s
readreverse  :      29.423 micros/op 33987 ops/sec; 3319.6 MB/s
readreverse  :      23.334 micros/op 42856 ops/sec; 4185.9 MB/s
readreverse  :      29.969 micros/op 33368 ops/sec; 3259.1 MB/s

avg : 3642.21 MB/s (1.5 X)

==> 10000_Keys_1MB.txt <==
readreverse  :     244.748 micros/op 4085 ops/sec; 4085.9 MB/s
readreverse  :     230.208 micros/op 4343 ops/sec; 4344.0 MB/s
readreverse  :     235.655 micros/op 4243 ops/sec; 4243.6 MB/s
readreverse  :     235.730 micros/op 4242 ops/sec; 4242.2 MB/s
readreverse  :     237.346 micros/op 4213 ops/sec; 4213.3 MB/s
readreverse  :     227.306 micros/op 4399 ops/sec; 4399.4 MB/s
readreverse  :     194.957 micros/op 5129 ops/sec; 5129.4 MB/s
readreverse  :     238.359 micros/op 4195 ops/sec; 4195.4 MB/s
readreverse  :     221.588 micros/op 4512 ops/sec; 4513.0 MB/s
readreverse  :     235.911 micros/op 4238 ops/sec; 4239.0 MB/s

avg : 4360.52 MB/s (1.38 X)
```

Test Plan: COMPILE_WITH_ASAN=1 make check -j64

Reviewers: andrewkr, yhchiang, sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D56511

Summary: Release RocksDB 4.8.0

Test Plan: N/A

Reviewers: sdong, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57525

Using explicit 64-bit type in conditional in platforms above 32-bits
This appears to be necessary on Mac OSX as std::conditional does not appear to short circuit and evaluates the third template arg
Making the third template arg be 64 bits explicitly works around this problem and will work on both 32 bit and 64+ bit platforms.