@Override
  public void pin(ICachedMNode node) throws MetadataException {
    pin(node, true);
  }
Currently, this method is only used for pin node get from mNodeCache. Pin MNode in memory makes
the pinned node and its ancestors not be evicted during cache eviction. The pinned MNode will
occupy memory resource, thus this method will check the memory status which may trigger cache
eviction or flushing.

@param node
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/schemaregion/mtree/impl/pbtree/CachedMTreeStore.java