Don't let flush preempt compaction in certain cases

Summary:
I have an application configured with 16 background threads. Write rates are high. L0->L1 compactions is very slow and it limits the concurrency of the system. While it's happening, other 15 threads are idle. However, when there is a need of a flush, that one thread busy with L0->L1 is doing flush, instead of any other 15 threads that are just sitting there.

This diff prevents that. If there are threads that are idle, we don't let flush preempt compaction.

Test Plan: Will run stress test

Reviewers: ljin, sdong, yhchiang

Reviewed By: sdong, yhchiang

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D22299
Fix ios compile

Summary: We need to set contbuild for this :)

Test Plan: compiles

Reviewers: sdong, yhchiang, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D22701
Fix compile

Summary: gcc on our dev boxes is not happy about __attribute__((unused))

Test Plan: compiles now

Reviewers: sdong, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D22707
Refactor PerfStepTimer to stop on destruct

This eliminates the need to remember to call PERF_TIMER_STOP when a section has
been timed. This allows more useful design with the perf timers and enables
possible return value optimizations. Simplistic example:

class Foo {
  public:
    Foo(int v) : m_v(v);
  private:
    int m_v;
}

Foo makeFrobbedFoo(int *errno)
{
  *errno = 0;
  return Foo();
}

Foo bar(int *errno)
{
  PERF_TIMER_GUARD(some_timer);

  return makeFrobbedFoo(errno);
}

int main(int argc, char[] argv)
{
  Foo f;
  int errno;

  f = bar(&errno);

  if (errno)
    return -1;
  return 0;
}

After bar() is called, perf_context.some_timer would be incremented as if
Stop(&perf_context.some_timer) was called at the end, and the compiler is still
able to produce optimizations on the return value from makeFrobbedFoo() through
to main().
fix dropping column family bug

Summary: 1. db/db_impl.cc:2324 (DBImpl::BackgroundCompaction) should not raise bg_error_ when column family is dropped during compaction.

Test Plan: 1. db_stress

Reviewers: ljin, yhchiang, dhruba, igor, sdong

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D22653
Merge pull request #242 from tdfischer/perf-timer-destructors

Refactor PerfStepTimer to automatically stop on destruct
add assert to db Put in db_stress test

Summary:
1. assert db->Put to be true in db_stress
2. begin column family with name "1".

Test Plan: 1. ./db_stress

Reviewers: ljin, yhchiang, dhruba, sdong, igor

Reviewed By: sdong, igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D22659
Ignore missing column families

Summary:
Before this diff, whenever we Write to non-existing column family, Write() would fail.

This diff adds an option to not fail a Write() when WriteBatch points to non-existing column family. MongoDB said this would be useful for them, since they might have a transaction updating an index that was dropped by another thread. This way, they don't have to worry about checking if all indexes are alive on every write. They don't care if they lose writes to dropped index.

Test Plan: added a small unit test

Reviewers: sdong, yhchiang, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D22143
call SanitizeDBOptionsByCFOptions() in the right place

Summary: It only covers Open() with default column family right now

Test Plan: make release

Reviewers: igor, yhchiang, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D22467
Merge pull request #1 from facebook/master

merge facebook/rocksdb back