@Override
    public long getTerm(long index) {
        final LogEntry entry = getEntry(index);
        if (entry != null) {
            return entry.getId().getTerm();
        }
        return 0;
    }
First log index and last log index key in configuration column family.
jraft-extension/bdb-log-storage-impl/src/main/java/com/alipay/sofa/jraft/storage/impl/BDBLogStorage.java