add kEntryRangeDeletion

Summary:
When there are many range deletions in a range, we want to trigger manual compaction on this range to reclaim disk space as soon as possible and speed up read.
After this change, we can collect informations of range deletions and store them into user properties which can guide our manual compaction.
Closes https://github.com/facebook/rocksdb/pull/3695

Differential Revision: D7570322

Pulled By: ajkr

fbshipit-source-id: c358fa43b0aac6cc954d2eadc7d3bd8015373369

db/dbformat.cc

@@ -46,6 +46,8 @@ EntryType GetEntryType(ValueType value_type) {
       return kEntrySingleDelete;
     case kTypeMerge:
       return kEntryMerge;
+    case kTypeRangeDeletion:
+      return kEntryRangeDeletion;
     default:
       return kEntryOther;
   }

include/rocksdb/types.h

@@ -22,6 +22,7 @@ enum EntryType {
   kEntryDelete,
   kEntrySingleDelete,
   kEntryMerge,
+  kEntryRangeDeletion,
   kEntryOther,
 };