@Override
  public void addBackToBufferAfterFlushFailure(ICachedMNode subTreeRoot) {
    put(subTreeRoot.getCacheEntry(), subTreeRoot);
  }
The ancestors of the volatile nodes. If a node is not volatile but not in nodeCache, it means
this node is an ancestor of some volatile node. Any volatile node is contained in the
CachedContainer of its parent. The parent will be placed in nodeBuffer. If the parent is volatile
as well, then the parent of the parent will be hold nodeBuffer instead, which means the root node
of a maximum volatile subtree will be placed in node buffer.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/schemaregion/mtree/impl/pbtree/memory/buffer/NodeBuffer.java