private int findSliceIndex(long passThroughIndex) {
    // find the last index that is less than or equal to passThroughIndex
    int left = 0;
    int right = startOffsets.size() - 1;
    int result = -1;

    while (left <= right) {
      int mid = left + (right - left) / 2;
      if (startOffsets.get(mid) <= passThroughIndex) {
        result = mid;
        left = mid + 1;
      } else {
        right = mid - 1;
      }
    }
    return result;
  }
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