Measure compaction time.

Summary: just record time consumed in compaction

Test Plan: compile

Reviewers: dhruba

Reviewed By: dhruba

CC: leveldb

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

db/db_impl.cc

@@ -1690,7 +1690,9 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
 
   CompactionStats stats;
   stats.micros = env_->NowMicros() - start_micros - imm_micros;
-
+  if (options_.statistics) {
+    options_.statistics->measureTime(COMPACTION_TIME, stats.micros);
+  }
   stats.files_in_leveln = compact->compaction->num_input_files(0);
   stats.files_in_levelnp1 = compact->compaction->num_input_files(1);
 

db/db_impl.h

@@ -275,7 +275,7 @@ class DBImpl : public DB {
   // Per level compaction stats.  stats_[level] stores the stats for
   // compactions that produced data for the specified "level".
   struct CompactionStats {
-    int64_t micros;
+    uint64_t micros;
 
     // Bytes read from level N during compaction between levels N and N+1
     int64_t bytes_readn;

include/leveldb/statistics.h

@@ -49,7 +49,8 @@ enum Tickers {
 enum Histograms {
   DB_GET = 0,
   DB_WRITE = 1,
-  HISTOGRAM_ENUM_MAX = 2,
+  COMPACTION_TIME = 2,
+  HISTOGRAM_ENUM_MAX = 3,
 };
 
 struct HistogramData {