public synchronized void initializeFrom(RegionVersionHolder<T> source) {
    // Make sure the bitsets are merged in both the source
    // and this vector
    mergeBitSet();

    RegionVersionHolder<T> other = source.clone();
    other.mergeBitSet();
    // Get a copy of the local version and exceptions
    long myVersion = version;

    // initialize our version and exceptions to match the others
    exceptions = other.exceptions;
    version = other.version;



    // Now if this.version/exceptions overlap with myVersion/myExceptions, use this'
    // The only case needs special handling is: if myVersion is newer than this.version,
    // should create an exception (this.version+1, myversion) and set this.version=myversion
    if (myVersion > version) {
      RVVException e = RVVException.createException(version, myVersion + 1);
      // add special exception
      if (exceptions == null) {
        exceptions = new LinkedList<>();
      }
      int i = 0;
      for (RVVException exception : exceptions) {
        if (e.compareTo(exception) >= 0) {
          break;
        }
        i++;
      }
      exceptions.add(i, e);
      version = myVersion;
    }

    // Initialize the bit set to be empty. Merge bit set should
    // have already done this, but just to be sure.
    if (bitSet != null) {
      bitSetVersion = version;
      // Make sure the bit set is empty except for the first, bit, indicating
      // that the version has been received.
      bitSet.set(0);
    }
  }
Initialize this version holder from another version holder This is called during GII.

It's more likely that the other holder has seen most of the versions, and this version holder
only has a few updates that happened since the GII started. So we apply our seen versions to
the other version holder and then initialize this version holder from the other version holder.
geode-core/src/main/java/org/apache/geode/internal/cache/versions/RegionVersionHolder.java