Remove compact cursor when split sub-compactions (#10289)

Summary:
In round-robin compaction priority, when splitting the compaction into sub-compactions, the earlier implementation takes into account the compact cursor to have full use of available sub-compactions. But this may result in unbalanced sub-compactions, so we remove this here.  The removal does not affect the cursor-based splitting mechanism within a sub-compaction, and thus the output files are still ensured to be split according to the cursor.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10289

Reviewed By: ajkr

Differential Revision: D37559091

Pulled By: littlepig2013

fbshipit-source-id: b8b45b99f63b09cf873f7f049bcb4ab13871fffc

db/compaction/compaction_job.cc

@@ -641,16 +641,6 @@ void CompactionJob::GenSubcompactionBoundaries() {
     }
   }
 
-  Slice output_split_user_key;
-  const InternalKey output_split_key = c->GetOutputSplitKey();
-  if (output_split_key.Valid()) {
-    output_split_user_key = ExtractUserKey(output_split_key.Encode());
-    bounds.emplace_back(output_split_key.Encode());
-  } else {
-    // Empty user key indicates that splitting is not required here
-    output_split_user_key = Slice();
-  }
-
   std::sort(bounds.begin(), bounds.end(),
             [cfd_comparator](const Slice& a, const Slice& b) -> bool {
               return cfd_comparator->Compare(ExtractUserKey(a),
@@ -721,10 +711,7 @@ void CompactionJob::GenSubcompactionBoundaries() {
         // need to put an end boundary
         continue;
       }
-      if (sum >= mean ||
-          (!output_split_user_key.empty() &&
-           cfd_comparator->Compare(ExtractUserKey(ranges[i].range.limit),
-                                   output_split_user_key) == 0)) {
+      if (sum >= mean) {
         boundaries_.emplace_back(ExtractUserKey(ranges[i].range.limit));
         sizes_.emplace_back(sum);
         subcompactions--;