message: Import text reserve optimization
diff: @@ -228,6 +228,7 @@ struct SqlCsvScope: public SqlExpressionMldbScope {
  {
  vector<ColumnPath> toKeep;
  std::vector<KnownColumn> columnsWithInfo;
  + size_t numToKeep = 0;
  for (unsigned i = 0; i < columnNames.size(); ++i) {
  const ColumnPath & columnName = columnNames[i];
  @@ -240,6 +241,7 @@ struct SqlCsvScope: public SqlExpressionMldbScope {
  columnsWithInfo.emplace_back(outputName,
  std::make_shared<AtomValueInfo>(),
  COLUMN_IS_DENSE);
  + ++numToKeep;
  }
  }
  @@ -259,12 +261,15 @@ struct SqlCsvScope: public SqlExpressionMldbScope {
  auto & row = scope.as<RowScope>();
  RowValue result;
  + result.reserve(numToKeep);
  for (unsigned i = 0; i < columnNames.size(); ++i) {
  if (!toKeep[i].empty())
  result.emplace_back(columnNames[i], row.row[i], row.ts);
  }
  + ExcAssertEqual(result.size(), numToKeep);
  +
  return result;
  };
  