@Override
    public int getDBFileSize() {
        return this.storeOptions.getIndexFileSize();
    }
Search the last segment log index and last conf log index from tail
@return pair of IndexEntry<last log index and position> (segment / conf)
jraft-extension/java-log-storage-impl/src/main/java/com/alipay/sofa/jraft/storage/db/IndexDB.java