JedisCluster : Scan For Key does not work

Question

I was trying to scan for particular key stored in JedisCluster.

String product = "MMATest";

String redisServer = "mycachecluster.eaogs8.0001.usw2.cache.amazonaws.com:6379,mycachecluster.eaogs8.0002.usw2.cache.amazonaws.com:6379";
    Set<HostAndPort> jedisClusterNode = new HashSet<>();
    String[] serversArray = redisServer.split(";");
    for (String aServersArray : serversArray) {
        jedisClusterNode.add(new HostAndPort(aServersArray.split(":")[0],
                Integer.valueOf(aServersArray.split(":")[1])));
    }
    JedisCluster jedisCluster = new JedisCluster(jedisClusterNode,
            buildPoolConfig());

ScanParams params = new ScanParams();
StringJoiner joiner = new StringJoiner("");
joiner.add("{");
joiner.add("Image-"+product);
joiner.add("}");
params.match(joiner.toString()).count(100);
System.out.println(joiner.toString());
ScanResult<String> scanResult = null;
String scanMarker = "0";
 do {
     scanResult = jedisCluster.scan(ScanParams.SCAN_POINTER_START, params);
      System.out.println(scanResult.getResult());
             System.out.println(!(scanResult.getResult() == null || scanResult.getResult().isEmpty()));

         } while (!scanMarker.equals("0"));

        ScanResult<Map.Entry<String,String>> scan = jedisCluster.hscan(joiner.toString(), ScanParams.SCAN_POINTER_START);
        System.out.println(scan.getResult());

Here I was getting the null value. But there is a value stored in the cluster node.

But if I try to scan the each Jedis pool, I will get the result.

  Map<String, JedisPool> jedisPools = jedisCluster.getClusterNodes();
         Set<String>jedisPoolList = jedisPools.keySet();
         System.out.println(jedisPools.keySet());
         System.out.println(jedisPools.values());
         System.out.println(jedisPools.size());
         for (String hostAndPort : jedisPoolList) {
             String[] parts = hostAndPort.split(":");
             String host = parts[0];
             int port = Integer.valueOf(parts[1]);
             try (Jedis jedis = new Jedis(host, port)) {
                 ScanParams params = new ScanParams().match("Image-"+product).count(100);
                 String scanMarker = "0";
                 ScanResult<String> results = null;

                 do {
                     results = jedis.scan(scanMarker, params);
                     System.out.println("XXXX"+results.getResult());
                     System.out.println("XXXX"+!(results.getResult() == null || results.getResult().isEmpty()));

                 } while (!scanMarker.equals("0"));
             }
         }

Why the JedisCluster scan method does not give the proper result? How do I solve this issue?

Note: I can use jedisCluster.exists(key) to check the key's existence. But I need to use scan as I can use the same interface to both Jedis and JedisCluster.

Answer 1

Part 1:

In your implementation with Jedis, you are matching Image-MMATest. As you are getting data, it proves that data is stored by that key.

However, with JedisCluster implementation, you have enclosed "Image-"+product with curly braces. Which means you are actually matching {Image-MMATest}. Your are not getting any data, because no data is stored by that key.

Part 2:

In JedisCluster, scan support is limited to Redis hash tag pattern. Image-MMATest is not Redis hash tag compliant pattern. Because of that you won't be able to get Image-MMATest using scan of JedisCluster.

To get data by scan of JedisCluster, you'd have to store data against a key which is Redis hash tag compliant pattern, e.g. {Image-MMATest}.

More details about Redis hash tag can be found in this documentation.