private boolean saveFirstLogIndex(final long logIndex) {
        try {
            this.firstLogIndexCheckpoint.setFirstLogIndex(logIndex);
            return this.firstLogIndexCheckpoint.save();
        } catch (final IOException e) {
            LOG.error("Error when save first log index", e);
            return false;
        }
    }
Generate ordered index entry array by using tow-way merging algorithm
@param segmentLogIterator segment log iterator
@param confLogIterator conf log iterator
@return ordered index entry array
jraft-extension/java-log-storage-impl/src/main/java/com/alipay/sofa/jraft/storage/LogitLogStorage.java