public boolean containsKey(K key) {
    return memoryMap.containsKey(key)
        || diskBasedMap.map(diskMap -> diskMap.containsKey(key)).orElse(false);
  }
Approximate memory footprint of the in-memory map.
amoro-format-iceberg/src/main/java/org/apache/amoro/utils/map/SimpleSpillableMap.java