Test Plan: make check

Reviewers: dhruba, haobo

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D10575

Summary:
Our ticker was not atomic. This was based on the assumption that we will increment counts at places only protected by Mutex. This is hard to program for and easy to make mistakes (mutex may be held a few layers above etc).
Also this increases the instructions executed when the mutex is held.

Test Plan: make check

Reviewers: haobo, dhruba

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D10569

Summary:
Earlier Statistics object was a raw pointer. This meant the user had to clear up
the Statistics object after creating the database. In most use cases the database is created in a function and the statistics pointer is out of scope. Hence the statistics object would never be deleted.
Now Using a shared_ptr to manage this.

Want this in before the next release.

Test Plan: make all check.

Reviewers: dhruba, emayanke

Reviewed By: emayanke

CC: leveldb

Differential Revision: https://reviews.facebook.net/D9735

Summary:
Use only the counter mechanism. Do away with
incNumFileOpens, incNumFileClose, incNumFileErrors
s/NULL/nullptr/g in db/table_cache.cc

Test Plan: make clean check

Reviewers: dhruba, heyongqiang, emayanke

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D8841

Summary: just record time consumed in compaction

Test Plan: compile

Reviewers: dhruba

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D8781

Summary:
* Counters for bytes read and write.
as a part of this diff, I want to=>
* Measure compaction times. @dhruba can you point which function, should
* I time to get Compaction-times. Was looking at CompactRange.

Test Plan: db_test

Reviewers: dhruba, emayanke

CC: leveldb

Differential Revision: https://reviews.facebook.net/D8763

Summary:
* Introduce is histogram in statistics.h
* stop watch to measure time.
* introduce two timers as a poc.
Replaced NULL with nullptr to fight some lint errors
Should be useful for google.

Test Plan:
ran db_bench and check stats.
make all check

Reviewers: dhruba, heyongqiang

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D8637

Summary: Add Tickers to count Write's and Get's

Test Plan: make check

Reviewers: dhruba, chip

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D7977

Summary: Record BloomFliter hits and drop off reasons during compaction.

Test Plan: Unit tests work.

Reviewers: dhruba, heyongqiang

Reviewed By: dhruba

Differential Revision: https://reviews.facebook.net/D6591

Summary:
Prototype stat's collection. Diff is a good estimate of what
the final code will look like.
A few assumptions :
  * Used a global static instance of the statistics object. Plan to pass
  it to each internal function. Static allows metrics only at app
  level.
  * In the Ticker's do not do any locking. Depend on the mutex at each
   function of LevelDB. If we ever remove the mutex, we should change
   here too. The other option is use atomic objects anyways as there
   won't be any contention as they will be always acquired only by one
   thread.
  * The counters are dumb, increment through lifecycle. Plan to use ods
    etc to get last5min stat etc.

Test Plan:
made changes in db_bench
Ran ./db_bench --statistics=1 --num=10000 --cache_size=5000
This will print the cache hit/miss stats.

Reviewers: dhruba, heyongqiang

Differential Revision: https://reviews.facebook.net/D6441

Summary:
Clean up compiler warnings generated by -Wall option.
make clean all OPT=-Wall

This is a pre-requisite before making a new release.

Test Plan: compile and run unit tests

Reviewers: heyongqiang

Reviewed By: heyongqiang

Differential Revision: https://reviews.facebook.net/D5019

Summary:
The db_bench test was not using the specified value for the max-file-open. Fixed.

The fs readhead is switched off.

Gather statistics about the table cache and print it out at the end of the tets run.

Test Plan: Revert Plan:

Reviewers: adsharma, sc

Reviewed By: adsharma

Differential Revision: https://reviews.facebook.net/D3441