public byte[] encode() {
        byte[] ps = AsciiStringUtil.unsafeEncode(this.fileName);
        byte[] bs = new byte[20 + ps.length];
        Bits.putLong(bs, 0, this.flushPosition);
        Bits.putLong(bs, 8, this.lastLogIndex);
        Bits.putInt(bs, 16, ps.length);
        System.arraycopy(ps, 0, bs, 20, ps.length);
        return bs;
    }
flushPosition (8 bytes) + lastLogIndex (8 bytes) + path(4 bytes len + string bytes)
jraft-extension/java-log-storage-impl/src/main/java/com/alipay/sofa/jraft/storage/file/assit/FlushStatusCheckpoint.java