Get complete Map from Redis if a key contains a String

Question

I am able to add and get a particular user object from Redis I am adding object like this:

 private static final String USER_PREFIX = ":USER:";
 public void addUserToRedis(String serverName,User user) {
 redisTemplate.opsForHash().put(serverName + USER_PREFIX + user.getId(), 
 Integer.toString(user.getId()),user); 
 }

If a userId is 100 I am able to get by key: SERVER1:USER:100
Now I want to retrieve all Users as Map<String,List<User>> ,
For example, get all users by this key SERVER1:USER:
Is it possible ? Or I need to modify my addUserToRedis method? Please suggest me.

• Visakh Vijayan: You can do a wildcard search. "SERVER:USER:*". Check pattern search in redis
• MostlyJava: It's working with wildcard searches.

Answer 1

I would recommend not using the "KEYS" command in production as this can severely impact REDIS latencies (can even bring down the cluster if you have a large number of keys stored)
Instead, you would want to use a different command than plain GET/SET.

It would be better if you use a Sets or Hashes

127.0.0.1:6379> sadd server1 user1 user2
(integer) 2
127.0.0.1:6379> smembers server1
1) "user2"
2) "user1"
127.0.0.1:6379>

Using sets you can simply add your users to server keys and get the entire list of users on a server.

If you really need a map of < server, list < users > > you can use hashes with stringified user data and then convert it to actual User POJO at application layer

127.0.0.1:6379> hset server2 user11 name
(integer) 1
127.0.0.1:6379> hset server2 user13 name
(integer) 1
127.0.0.1:6379> hgetall server2
1) "user11"
2) "name"
3) "user13"
4) "name"
127.0.0.1:6379>

Also do note that keeping this much big data into a single key is not an ideal thing to do.

Answer 2

i dont use java but here's how to use SCAN

const Redis = require('ioredis')
const redis = new Redis()
async function main() {
 const stream = redis.scanStream({
 match: "*:user:*",
 count: 100,
 })
 stream.on("data", (resultKeys) => {
 for (let i = 0; i < resultKeys.length; i++) {
 // console.log(resultKeys[i])
 // do your things here
 }
 });
 stream.on("end", () => {
 console.log("all keys have been visited");
 });
}
main()

Answer 3

Finally I came up with this solution with wildcard search and avoiding KEYS, and here is my complete method:

 public Map<String, User> getUserMapFromRedis(String serverName){
 Map<String, User> users=new HashMap<>();
 RedisConnection redisConnection = null;
 try {
 redisConnection = redisTemplate.getConnectionFactory().getConnection();
 ScanOptions options = ScanOptions.scanOptions().match(serverName + USER_PREFIX+"*").build();
 Cursor<byte[]> scan = redisConnection.scan(options);
 while (scan.hasNext()) {
 byte[] next = scan.next();
 String key = new String(next, StandardCharsets.UTF_8);
 String[] keyArray=key.split(":");
 String userId=keyArray[2];
 User user=//get User by userId From Redis
 users.put(userId, user);
 }
 try {
 scan.close();
 } catch (IOException e) {
 
 }
 }finally {
 redisConnection.close(); //Ensure closing this connection.
 }
 return users;
 }

• Tuan Anh Tran: KEYS would block redis server. if must, you can try using SCAN
• MostlyJava: @TuanAnhTran can you guide me that how to use with redisTemplate in this scenario, this will be very helpful
• Tuan Anh Tran: I dont use java but here's how to do it with nodejs stackoverflow.com/a/64007618/2688699
• MostlyJava: @TuanAnhTran I edited my answer to avoid using KEYS, now I am using SCAN. This one is fine?
• Tuan Anh Tran: yeah should be fine. you can test by creating few millions key and see for your self :)