@Override
  public ICachedMNode read(short segIdx, String key) throws MetadataException {
    return getSegment(segIdx).getRecordByKey(key);
  }
This class is aimed to manage space inside one page.

<p>A segment inside a page has 3 representation: index, offset and instance. <br>

<ul>
  <li>Index is meant to decouple file-wide indexing with in-page compaction
  <li>Offset is meant for in-page indexing
  <li>Segment instance is meant for records manipulations
</ul>

<b>Page Header Structure as in {@linkplain ISchemaPage}.</b>

<p>Page Body Structure:

<ul>
  <li>var length * memberNum: {@linkplain WrappedSegment} contains serialized ICacheMNodes.
  <li>... spare space...
  <li>2 bytes * memberNum: offset of segments, using marking deletion as {@linkplain
      #deleteSegment} mentioned.
</ul>
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/schemaregion/mtree/impl/pbtree/schemafile/SegmentedPage.java