db_bench: add a mode to operate multiple DBs

Summary: This patch introduces a new parameter num_multi_db in db_bench. When this parameter is larger than 1, multiple DBs will be created. In all benchmarks, any operation applies to a random DB among them. This is to benchmark the performance of similar applications.

Test Plan: run db_bench on both of num_multi_db=0 and more.

Reviewers: haobo, ljin, igor

Reviewed By: igor

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

Differential Revision: https://reviews.facebook.net/D17769
using thread local SuperVersion for NewIterator

Summary:
Similar to GetImp(), use SuperVersion from thread local instead of acquriing mutex.
I don't expect this change will make a dent on NewIterator() performance
because the bottleneck seems to be on the rest part of the API

Test Plan:
make asan_check
will post perf numbers

Reviewers: haobo, igor, sdong, dhruba, yhchiang

Reviewed By: sdong

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17643
thread local for tailing iterator

Summary:
replace the super version acquisision in tailing itrator with thread
local

Test Plan: will post results

Reviewers: igor, haobo, sdong, yhchiang, dhruba

Reviewed By: igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17757
Fix merge_test failure due to incorrect assert behavior in the release mode.
Expose in memory Env to the world

Summary: That will help with some iOS testing I'm doing.

Test Plan: compiles

Reviewers: dhruba, haobo, ljin, yhchiang, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17787
[JNI] Each set function of Options / WriteOptions now returns its option instance.

Summary:
Make each set function of Options / WriteOptions return its option instance.
Java developers can now easier specify each option like the following:

    options.setCreateIfMissing(true)
        .setWriteBufferSize(8 * 1024)
        .setMaxWriteBufferNumber(3)
        .setDisableSeekCompaction(true)
        .setBlockSize(64 * 1024)
        .setMaxBackgroundCompactions(10);

Test Plan:
make rocksdbjava
make jtest

Reviewers: haobo, ankgup87, sdong, dhruba

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17661
[JAVA] Add java binding for Options.block_cache.

Summary:
Add java bindings for Options.block_cache and allow DbBenchmark to
set cache_size.

Test Plan:
make rocksdbjava
make jtest
make jdb_Bench

Reviewers: haobo, sdong, ankgup87

Reviewed By: ankgup87

CC: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D17481
[Java] Add SizeUnit in org.rocksdb.util to store const like KB, GB.

Summary:
* Add a class SizeUnit to store frequently used consts.  Currently
  it has KB, MB, GB, TB, and PB.

* Change the parameter type of Options.writeBufferSize and Options.blockSize
  from int to long.

Test Plan:
make rocksdbjava
make jtest

Reviewers: haobo, ankgup87, sdong, dhruba

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17703
Fix compile error in tailing_iter.h

Summary:
Fix the following compile error

  ./db/tailing_iter.h:17:1: error: class 'SuperVersion' was previously declared as a struct [-Werror,-Wmismatched-tags]
  class SuperVersion;
  ^
  ./db/column_family.h:77:8: note: previous use is here
  struct SuperVersion {
         ^
         ./db/tailing_iter.h:17:1: note: did you mean struct here?
         class SuperVersion;
         ^~~~~
         struct
         1 error generated.

Test Plan: make

Reviewers: ljin, igor, haobo, sdong

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17799
Fix db_bench's multireadrandom

Summary: multireadrandom is broken. Fix it

Test Plan: run it and see segfault has gone.

Reviewers: ljin

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17781
Add statistics object
Add statistics
Remove unused headers
remove unused header
Add newline at end of file
Don't roll empty logs

Summary:
With multiple column families, especially when manual Flush is executed, we might roll the log file, although the current log file is empty (no data has been written to the log).

After the diff, we won't create new log file if current is empty.

Next, I will write an algorithm that will flush column families that reference old log files (i.e., that weren't flushed in a while)

Test Plan: Added an unit test. Confirmed that unit test failes in master

Reviewers: dhruba, haobo, ljin, sdong

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17631
Set log_empty to false even when options.sync is off [fix tests]
Don't compile ldb tool into static library

Summary:
This is first step of my effort to reduce size of librocksdb.a for use in mobile.

ldb object files are huge and are ment to be used as a command line tool. I moved them to `tools/` directory and include them only when compiling `ldb`

This diff reduced librocksdb.a from 42MB to 39MB on my mac (not stripped).

Test Plan: ran ldb

Reviewers: dhruba, haobo, sdong, ljin, yhchiang

Reviewed By: yhchiang

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17823
Fix sst_dump and reduce_levels_test compile errors
Revert "Fix sst_dump and reduce_levels_test compile errors"

This reverts commit d8f00b4109e3df10be56141f3ff3ba9b0d10f585.