Fix DeleteRange including sentinels in output files

Summary:
when writing RangeDelAggregator::AddToBuilder, I forgot that there are sentinel tombstones in the middle of the interval map since gaps between real tombstones are represented with sentinels.

blame: #1614
Closes https://github.com/facebook/rocksdb/pull/1804

Differential Revision: D4460426

Pulled By: ajkr

fbshipit-source-id: 69444b5

db/db_range_del_test.cc

@@ -165,6 +165,28 @@ TEST_F(DBRangeDelTest, MaxCompactionBytesCutsOutputFiles) {
   db_->ReleaseSnapshot(snapshot);
 }
 
+TEST_F(DBRangeDelTest, SentinelsOmittedFromOutputFile) {
+  // Regression test for bug where sentinel range deletions (i.e., ones with
+  // sequence number of zero) were included in output files.
+  // snapshot protects range tombstone from dropping due to becoming obsolete.
+  const Snapshot* snapshot = db_->GetSnapshot();
+
+  // gaps between ranges creates sentinels in our internal representation
+  std::vector<std::pair<std::string, std::string>> range_dels = {{"a", "b"}, {"c", "d"}, {"e", "f"}};
+  for (const auto& range_del : range_dels) {
+    ASSERT_OK(db_->DeleteRange(WriteOptions(), db_->DefaultColumnFamily(),
+                               range_del.first, range_del.second));
+  }
+  ASSERT_OK(db_->Flush(FlushOptions()));
+  ASSERT_EQ(1, NumTableFilesAtLevel(0));
+
+  std::vector<std::vector<FileMetaData>> files;
+  dbfull()->TEST_GetFilesMetaData(db_->DefaultColumnFamily(), &files);
+  ASSERT_GT(files[0][0].smallest_seqno, 0);
+
+  db_->ReleaseSnapshot(snapshot);
+}
+
 TEST_F(DBRangeDelTest, FlushRangeDelsSameStartKey) {
   db_->Put(WriteOptions(), "b1", "val");
   ASSERT_OK(

db/range_del_aggregator.cc

@@ -420,9 +420,10 @@ void RangeDelAggregator::AddToBuilder(
       RangeTombstone tombstone;
       if (collapse_deletions_) {
         auto next_tombstone_map_iter = std::next(tombstone_map_iter);
-        if (next_tombstone_map_iter == stripe_map_iter->second.raw_map.end()) {
-          // it's the sentinel tombstone
-          break;
+        if (next_tombstone_map_iter == stripe_map_iter->second.raw_map.end() ||
+            tombstone_map_iter->second.seq_ == 0) {
+          // it's a sentinel tombstone
+          continue;
         }
         tombstone.start_key_ = tombstone_map_iter->first;
         tombstone.end_key_ = next_tombstone_map_iter->first;