@Override
  public void fromDelta(DataInput in) throws IOException, InvalidDeltaException {
    maxInactiveInterval = in.readInt();
    lastAccessedTime = in.readLong();
    Map<String, DeltaEvent> localDeltas = new HashMap<>();
    try {
      int size = DataSerializer.readInteger(in);
      for (int i = 0; i < size; i++) {
        String key = DataSerializer.readString(in);
        DeltaEvent evt = DataSerializer.readObject(in);
        localDeltas.put(key, evt);
      }
    } catch (ClassNotFoundException ex) {
      LOG.error("Unable to de-serialize delta events", ex);
      return;
    }

    LOG.debug("Processing {} delta events for {}", localDeltas.size(), session);
    for (DeltaEvent e : localDeltas.values()) {
      if (e.isUpdate()) {
        attributes.put(e.getName(), e.getValue());
      } else {
        attributes.remove(e.getName());
      }
    }
    jvmOwnerId = in.readUTF();
  }
This map holds the updates to attributes
extensions/geode-modules-session-internal/src/main/java/org/apache/geode/modules/session/internal/filter/attributes/AbstractDeltaSessionAttributes.java