Relax an assertion in Compaction::ShouldStopBefore

Summary:
In some case, it is possible to have two concesutive SST files might sharing
same boundary keys.  However, in the assertion in Compaction::ShouldStopBefore,
it exclude such possibility.

This patch fix this issue by relaxing the assertion to allow the equal case.

Test Plan: rocksdb tests

Reviewers: IslamAbdelRahman, kradhakrishnan, sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D55875

db/compaction_job.cc

@@ -104,13 +104,12 @@ struct CompactionJob::SubcompactionState {
   uint64_t num_output_records;
   CompactionJobStats compaction_job_stats;
   uint64_t approx_size;
-  // An index that used to speed up Compaction::ShouldStopBefore().
+  // An index that used to speed up ShouldStopBefore().
   size_t grandparent_index = 0;
   // The number of bytes overlapping between the current output and
-  // grandparent files used in Compaction::ShouldStopBefore().
+  // grandparent files used in ShouldStopBefore().
   uint64_t overlapped_bytes = 0;
-  // A flag determine whether the key has been seen in
-  // Compaction::ShouldStopBefore()
+  // A flag determine whether the key has been seen in ShouldStopBefore()
   bool seen_key = false;
 
   SubcompactionState(Compaction* c, Slice* _start, Slice* _end,
@@ -174,7 +173,7 @@ struct CompactionJob::SubcompactionState {
       assert(grandparent_index + 1 >= grandparents.size() ||
              icmp->Compare(
                  grandparents[grandparent_index]->largest.Encode(),
-                 grandparents[grandparent_index + 1]->smallest.Encode()) < 0);
+                 grandparents[grandparent_index + 1]->smallest.Encode()) <= 0);
       grandparent_index++;
     }
     seen_key = true;