Minor compaction logging improvements
1) make summary less likely to be truncated
2) format human-readable file sizes in summary
3) log the motivation for each universal compaction
An initial implementation of kCompactionStopStyleSimilarSize for universal compaction
address code review comments on 5e3aeb5f8e
- reduce string copying in Compaction::Summary
- simplify file number checking in UniversalCompactionStopStyleSimilarSize unit test
Some fixes to BackupableDB

Summary:
(1) Report corruption if backup meta file has tailing data that was not read. This should fix: https://github.com/facebook/rocksdb/issues/81 (also, @sdong reported similar issue)
(2) Don't use OS buffer when copying file to backup directory. We don't need the file in cache since we won't be reading it twice
(3) Don't delete newer backups when somebody tries to backup the diverged DB (restore from older backup, add new data, try to backup). Rather, just fail the new backup.

Test Plan: backupable_db_test

Reviewers: ljin, dhruba, sdong

Reviewed By: ljin

CC: leveldb, sdong

Differential Revision: https://reviews.facebook.net/D16287
make key evenly distributed between 0 and FLAGS_num

Summary:
The issue is that when FLAGS_num is small, the leading bytes of the key
are padded with 0s. This makes all keys have the same prefix 00000000

Most of the changes are just to make lint happy

Test Plan: ran db_bench

Reviewers: sdong, haobo, igor

Reviewed By: sdong

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16317
Fix a buggy assert

Summary: The assert was pointless since if if prefix is the same as the whole key, assertion will surely fail. Reason behind is when performing the internal key comparison, if user keys are the same, *key with smaller transaction id* wins.

Test Plan: make -j32 && make check

Reviewers: sdong, dhruba, haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16551
CleanupIteratorState() only to initialize DeletionState when super version cleanup needed

Summary:
Two changes:
1. DeletionState is only constructed when cleaning up is needed
2. Fix the bug of deletion state construction bug. A change was made in a previous patch: https://reviews.facebook.net/rROCKSDB774ed89c2405ee058086b099cbc8b29e243739cc#71a34e2e However, it somehow got lost when merging

Test Plan: make all check

Reviewers: kailiu, haobo, igor

Reviewed By: igor

CC: igor, dhruba, i.am.jin.lei, yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D16233
CloseDB in BackupableDBTest to make valgrind happy
MergingIterator assertion

Summary: I wrote a test that triggers assertion in MergingIterator. I have not touched that code ever, so I'm looking for somebody with good understanding of the MergingIterator code to fix this. The solution is probably a one-liner. Let me know if you're willing to take a look.

Test Plan: This test fails with an assertion `use_heap_ == false`

Reviewers: dhruba, haobo, sdong, kailiu

Reviewed By: sdong

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16521
config max_background_flushes in db_bench

Summary: as title

Test Plan: make release

Reviewers: haobo, sdong, igor

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16437
fix db_bench to use HashSkipList for real

Summary:
For HashSkipList case, DBImpl has sanity check to see if prefix_extractor in
options is the same as the one in memtable factory. If not, it falls
back to SkipList. As result, I was experimenting with SkipList
performance. No wonder it is much worse than LinkedList

Test Plan: ran benchmark

Reviewers: haobo, sdong, igor

Reviewed By: igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16569
output perf_context in db_bench readrandom

Summary:
Add helper function to print perf context data in db_bench if enabled.
I didn't find any code that actually exports perf context data. Not sure
if I missed anything

Test Plan: ran db_bench

Reviewers: haobo, sdong, igor

Reviewed By: igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16575
Merge pull request #47 from mlin/kCompactionStopStyleSimilarSize

An initial implementation of kCompactionStopStyleSimilarSize for universal compaction
Merge branch 'master' into columnfamilies

Conflicts:
	db/db_impl.cc