@Override
  public void writeMNode(ICachedMNode node) throws MetadataException, IOException {
    SchemaPageContext cxt = new SchemaPageContext();
    threadContexts.put(Thread.currentThread().getId(), cxt);
    pagePool.cacheGuardian();
    entrantLock(node, cxt);
    try {
      writeNewChildren(node, cxt);
      writeUpdatedChildren(node, cxt);
      flushDirtyPages(cxt);
    } finally {
      releaseLocks(cxt);
      pagePool.releaseReferent(cxt);
      threadContexts.remove(Thread.currentThread().getId(), cxt);
    }
  }
Abstraction for various implementation of structure of pages. But multi-level index is hard-coded
within the framework since only alias works like secondary index now.

<p>Hierarchy of index may be decoupled from this framework in further improvement.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/schemaregion/mtree/impl/pbtree/schemafile/pagemgr/PageManager.java