public void addSlice(Slice slice) {
    slices.add(slice);
    if (startOffsets.isEmpty()) {
      startOffsets.add(0L);
    } else {
      startOffsets.add(
          startOffsets.get(startOffsets.size() - 1)
              + slices.get(startOffsets.size() - 1).getSize());
    }
    this.estimatedSize += slice.getEstimatedSize();
  }
Used to manage the slices of the partition. It is all in memory now.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/process/function/partition/PartitionCache.java