@Override
  public void clear() {
    memTableMap.clear();
    memSize = 0;
    seriesNumber = 0;
    totalPointsNum = 0;
    totalPointsNumThreshold = 0;
    tvListRamCost = 0;
    maxPlanIndex = 0;
    minPlanIndex = 0;
  }
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