@Override
  public long getTotalPointsNum() {
    return totalPointsNum;
  }
Create this MemChunk if it's not exist.

@param deviceId device id
@param schemaList measurement schemaList
@return this MemChunkGroup
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/memtable/AbstractMemTable.java