private void openDB(final List<ColumnFamilyDescriptor> columnFamilyDescriptors) throws RocksDBException {
        final List<ColumnFamilyHandle> columnFamilyHandles = new ArrayList<>();

        final File dir = new File(this.path);
        if (dir.exists() && !dir.isDirectory()) {
            throw new IllegalStateException("Invalid log path, it's a regular file: " + this.path);
        }
        this.db = RocksDB.open(this.dbOptions, this.path, columnFamilyDescriptors, columnFamilyHandles);

        assert (columnFamilyHandles.size() == 2);
        this.confHandle = columnFamilyHandles.get(0);
        this.defaultHandle = columnFamilyHandles.get(1);
    }
Save the first log index into conf column family.
jraft-core/src/main/java/com/alipay/sofa/jraft/storage/impl/RocksDBLogStorage.java