Some question about VersionSet::PickCompactionForGuards

[baiqiubai]

Why not add all files at the level level directly to guards_compaction_and_all_files instead of taking the intersection of Complete_guards and Guards? I'm a little confused about this code, so I'd appreciate explaining it 。
`

              int guard_index_iter = 0;
	  for (size_t i = 0; i < complete_guards.size(); i++) {
		  GuardMetaData* cg = complete_guards[i];
		  int guard_index = -1;
		  Slice guard_key = cg->guard_key.user_key(), next_guard_key;
		  if (i + 1 < complete_guards.size()) {
			  next_guard_key = complete_guards[i+1]->guard_key.user_key();
		  }

		  for (; guard_index_iter < guards.size(); guard_index_iter++) {
			  int compare = icmp_.user_comparator()->Compare(guards[guard_index_iter]->guard_key.user_key(), guard_key);
			  if (compare == 0) {
				  guard_index = guard_index_iter;
				  guard_index_iter++;
				  break;
			  } else if (compare > 0) {
				  break;
			  } else {
				  // Ideally it should never reach here since there are no duplicates in complete_guards and complete_guards is a superset of guards
			  }
		  }

		  if (guard_index == -1) { // If guard is not found for this complete guard
			  continue;
		  }
		  GuardMetaData* g = guards[guard_index];
		  bool guard_added = false;
		  for (unsigned j = 0; j < g->files.size(); j++) {
			  FileMetaData* file = g->file_metas[j];
			  Slice file_smallest = file->smallest.user_key();
			  Slice file_largest = file->largest.user_key();
			  if ((i < complete_guards.size()-1 							// If it is not the last guard, checking for smallest and largest to fit in the range
							  && (icmp_.user_comparator()->Compare(file_smallest, guard_key) < 0
									  || icmp_.user_comparator()->Compare(file_largest, next_guard_key) >= 0))
					  || (i == complete_guards.size()-1 						// If it is the last guard, checking for the smallest to fit in the guard
							  && icmp_.user_comparator()->Compare(file_smallest, guard_key) < 0)) {
				  guards_to_add_to_compaction.push_back(g);
				  guards_compaction_add_all_files.push_back(true);	
				  guard_added = true;
				  break; // No need to check other files
			  }
		  }
		  if (!guard_added && which == 0 && (force_compact || v->guard_compaction_scores_[current_level][guard_index] >= 1.0)) {
			  guards_to_add_to_compaction.push_back(g);
			  guards_compaction_add_all_files.push_back(false);
			  continue;
		  }
	  }

`