Serialize HashMap into Redis Using Kryo

Question

I am trying to under how Kryo serlization works. I have a very large HashMap which I would like to push into Redis . The HashMap is:

HashMap<String, HashMap<String, Set<Long>>> cache = new HashMap<>();

What is the fastest way to serialize into Redis ?

Option 1: Directly into Redis?

I see that you can use Kryo like:

Kryo kryo = new Kryo();
kryo.register(HashMap.class);
Output output = //For Redis what would the output be ?
kryo. writeObject(output, cache)

But I am confused as to what Output should be when using Redis .

Option 2: Via a byte array?

I have also seen that the following maybe possible:

Jedis jedis = new Jedis("localhost");
Kryo kryo = new Kryo();
kryo.register(HashMap.class);

ByteArrayOutputStream stream = new ByteArrayOutputStream();
Output output = new Output(stream);
kryo.writeObject(output, cache);
output.close();
byte[] buffer = stream.toByteArray();
jedis.set("Test", buffer);

But this seems inefficient to me as I am effectively "cloning" my large cache into a byte array.

What is an efficient approach for this problem ?

Answer 1

AFAIK there's no Redis output for Kryo. Jedis has only byte[] and String APIs so you can't use wrapped/pooled buffers.

Using Kryo is possible already with redisson as they provide a Kryo codec which uses ByteBuffer s. Alternatively, you could also use lettuce which is a low-level Redis driver providing also a codec API using ByteBuffer .