code: public void enableMmap() {
  		if (validState) {
  			throw new InvalidStateException();
  		}
  		if (Check64bitsJVM.JVMis64bits()) {
  			log.info("Enabled mmap on 64bits JVM");
  		} else {
  			log.warn("Enabled mmap on 32bits JVM, risk of: java.lang.OutOfMemoryError: Map failed");
  		}
  		useMmap = true;
  	}
docs: Enable mmap of files (default is not enabled), call before use {@link #open()}
  <p/>
  Recommended use of: {@link #enableMmapIfSupported()}
  <p/>
  <b>NOTE:</b> 32bit JVM can only address 2GB of memory, enable mmap can throw
  <b>java.lang.OutOfMemoryError: Map failed</b> exceptions