public void refer(ISchemaPage page) {
    if (!referredPages.containsKey(page.getPageIndex())) {
      page.incrementAndGetRefCnt();
      referredPages.put(page.getPageIndex(), page);
    }
  }
Thread local variables about write/update process.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/schemaregion/mtree/impl/pbtree/schemafile/pagemgr/SchemaPageContext.java