public synchronized void flushDirtyPages(SchemaPageContext cxt) throws IOException {
    if (cxt.dirtyCnt == 0) {
      return;
    }
    pageIOChannel.flushMultiPages(cxt);
    pagePool.appendBucketIndex(cxt);
    if (metric != null) {
      metric.recordFlushPageNum(cxt.referredPages.size());
    }
  }
Insert an entry of subordinate index of the target node.

@param base index of the top page contains sub-index entries.
@param key key of the sub-index entry.
@param rec value of the sub-index entry.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/schemaregion/mtree/impl/pbtree/schemafile/pagemgr/PageManager.java