Disallow SstFileWriter from creating empty sst files

Summary:
SstFileWriter may create an sst file with no entries
Right now this will fail when being ingested using DB::AddFile() saying that the keys are corrupted

Test Plan: make check

Reviewers: yhchiang, rven, anthony, sdong

Reviewed By: sdong

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D52815

db/db_impl.cc

@@ -3502,6 +3502,9 @@ Status DBImpl::AddFile(ColumnFamilyHandle* column_family,
   auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
   ColumnFamilyData* cfd = cfh->cfd();
 
+  if (file_info->num_entries == 0) {
+    return Status::InvalidArgument("File contain no entries");
+  }
   if (file_info->version != 1) {
     return Status::InvalidArgument("Generated table version is not supported");
   }

db/db_test.cc

@@ -8801,6 +8801,12 @@ TEST_F(DBTest, AddExternalSstFile) {
     ASSERT_EQ(file5_info.smallest_key, Key(400));
     ASSERT_EQ(file5_info.largest_key, Key(499));
 
+    // Cannot create an empty sst file
+    std::string file_empty = sst_files_folder + "file_empty.sst";
+    ExternalSstFileInfo file_empty_info;
+    s = sst_file_writer.Finish(&file_empty_info);
+    ASSERT_NOK(s);
+
     DestroyAndReopen(options);
     // Add file using file path
     s = db_->AddFile(file1);

table/sst_file_writer.cc

@@ -163,6 +163,9 @@ Status SstFileWriter::Finish(ExternalSstFileInfo* file_info) {
   if (!r->builder) {
     return Status::InvalidArgument("File is not opened");
   }
+  if (r->file_info.num_entries == 0) {
+    return Status::InvalidArgument("Cannot create sst file with no entries");
+  }
 
   Status s = r->builder->Finish();
   if (s.ok()) {