code: private long getOptimalPartSize(long contentLengthOfSource) {
  
          long optimalPartSize = TransferManagerUtils
                  .calculateOptimalPartSizeForCopy(copyObjectRequest,
                          configuration, contentLengthOfSource);
          log.debug("Calculated optimal part size: " + optimalPartSize);
          return optimalPartSize;
      }
docs: Computes and returns the optimal part size for the copy operation.