docs: private void startTransaction() throws IOException {
        try {
           tm.begin();
        }
        catch (Exception e) {
           log.unableToStartTransaction(e);
           throw new IOException("SharedLuceneLock could not start a transaction after having acquired the lock", e);
        }
        if (trace) {
           log.tracef("Batch transaction started for index: %s", indexName);
        }
     }