Fix CompactionJob::Install division by zero

Summary:
Fix CompactionJob::Install division by zero
Closes https://github.com/facebook/rocksdb/pull/1580

Differential Revision: D4240794

Pulled By: IslamAbdelRahman

fbshipit-source-id: 7286721

db/compaction_job.cc

@@ -590,6 +590,16 @@ Status CompactionJob::Install(const MutableCFOptions& mutable_cf_options) {
   VersionStorageInfo::LevelSummaryStorage tmp;
   auto vstorage = cfd->current()->storage_info();
   const auto& stats = compaction_stats_;
+
+  double read_write_amp = 0.0;
+  double write_amp = 0.0;
+  if (stats.bytes_read_non_output_levels > 0) {
+    read_write_amp = (stats.bytes_written + stats.bytes_read_output_level +
+                      stats.bytes_read_non_output_levels) /
+                     static_cast<double>(stats.bytes_read_non_output_levels);
+    write_amp = stats.bytes_written /
+                static_cast<double>(stats.bytes_read_non_output_levels);
+  }
   LogToBuffer(
       log_buffer_,
       "[%s] compacted to: %s, MB/sec: %.1f rd, %.1f wr, level %d, "
@@ -602,16 +612,10 @@ Status CompactionJob::Install(const MutableCFOptions& mutable_cf_options) {
       stats.bytes_written / static_cast<double>(stats.micros),
       compact_->compaction->output_level(),
       stats.num_input_files_in_non_output_levels,
-      stats.num_input_files_in_output_level,
-      stats.num_output_files,
+      stats.num_input_files_in_output_level, stats.num_output_files,
       stats.bytes_read_non_output_levels / 1048576.0,
       stats.bytes_read_output_level / 1048576.0,
-      stats.bytes_written / 1048576.0,
-      (stats.bytes_written + stats.bytes_read_output_level +
-       stats.bytes_read_non_output_levels) /
-          static_cast<double>(stats.bytes_read_non_output_levels),
-      stats.bytes_written /
-          static_cast<double>(stats.bytes_read_non_output_levels),
+      stats.bytes_written / 1048576.0, read_write_amp, write_amp,
       status.ToString().c_str(), stats.num_input_records,
       stats.num_dropped_records);