public BatchBackend makeBatchBackend(MassIndexerProgressMonitor progressMonitor, Integer forceToNumWriterThreads) {
final BatchBackend batchBackend;
String impl = configurationProperties.getProperty( Environment.BATCH_BACKEND );
if ( StringHelper.isEmpty( impl ) || "LuceneBatch".equalsIgnoreCase( impl ) ) {
batchBackend = new DefaultBatchBackend();
}
else {
batchBackend = ClassLoaderHelper.instanceFromName(
BatchBackend.class, impl, ImmutableSearchFactory.class,
"batchbackend"