Fix bug in Counters and record Sequencenumber using only TickerCount

Summary:
The way counters/statistics are implemented in rocksdb demands that enum Tickers and TickerNameMap follow the same order, otherwise statistics exposed from fbcode/rocks get out-of-sync. 2 counters for prefix had violated this order and when I built counters for fbcode/mcrocksdb, statistics for sequence number were appearing out-of-sync.
The other change is to record sequence-number using setTickerCount only and not recordTick. This is because of difference in statistics as understood by rocks/utils which uses ServiceData::statistics function and rocksdb statistics. In rocksdb there is just 1 counter for a countername. But in ServiceData there are 4 independent buckets for every countername-Count, Sum, Average and Rate. SetTickerCount and RecordTick update the same variable in rocksdb but different buckets in ServiceData. Therefore, I had to choose one consistent function from RecordTick or SetTickerCount for sequence number in rocksdb. I chose SetTickerCount because the statistics object in options passed during rocksdb-open is user-dependent and SetTickerCount makes sense there.
There will be a corresponding diff to mcorcksdb in fbcode shortly.

Test Plan: make all check; check ticker value using fprintfs

Reviewers: dhruba

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D12669

db/db_impl.cc

@@ -2468,7 +2468,7 @@ Status DBImpl::Write(const WriteOptions& options, WriteBatch* my_batch) {
           // have succeeded in memtable but Status reports error for all writes.
           throw std::runtime_error("In memory WriteBatch corruption!");
         }
-        RecordTick(options_.statistics, SEQUENCE_NUMBER, my_batch_count);
+        SetTickerCount(options_.statistics, SEQUENCE_NUMBER, last_sequence);
         versions_->SetLastSequence(last_sequence);
         last_flushed_sequence_ = current_sequence;
       }

include/rocksdb/statistics.h

@@ -75,8 +75,6 @@ const std::vector<std::pair<Tickers, std::string>> TickersNameMap = {
   { BLOCK_CACHE_MISS, "rocksdb.block.cache.miss" },
   { BLOCK_CACHE_HIT, "rocksdb.block.cache.hit" },
   { BLOOM_FILTER_USEFUL, "rocksdb.bloom.filter.useful" },
-  { BLOOM_FILTER_PREFIX_CHECKED, "rocksdb.bloom.filter.prefix.checked" },
-  { BLOOM_FILTER_PREFIX_USEFUL, "rocksdb.bloom.filter.prefix.useful" },
   { COMPACTION_KEY_DROP_NEWER_ENTRY, "rocksdb.compaction.key.drop.new" },
   { COMPACTION_KEY_DROP_OBSOLETE, "rocksdb.compaction.key.drop.obsolete" },
   { COMPACTION_KEY_DROP_USER, "rocksdb.compaction.key.drop.user" },
@@ -97,7 +95,9 @@ const std::vector<std::pair<Tickers, std::string>> TickersNameMap = {
   { NUMBER_MULTIGET_BYTES_READ, "rocksdb.number.multiget.bytes.read" },
   { NUMBER_FILTERED_DELETES, "rocksdb.number.deletes.filtered" },
   { NUMBER_MERGE_FAILURES, "rocksdb.number.merge.failures" },
-  { SEQUENCE_NUMBER, "rocksdb.sequence.number" }
+  { SEQUENCE_NUMBER, "rocksdb.sequence.number" },
+  { BLOOM_FILTER_PREFIX_CHECKED, "rocksdb.bloom.filter.prefix.checked" },
+  { BLOOM_FILTER_PREFIX_USEFUL, "rocksdb.bloom.filter.prefix.useful" }
 };
 
 /**