MemcachedClient.get will return null sometimes, but it has a correct value actually.

[sunchuanleihit]

MemcachedClient.get most times return the correct value ,but will return null sometimes. how can i fix it?
I use Spring Boot.

My Configuration

@Configuration
public class UserMemcacheConfig extends BaseConfig{

    @Value("${memcache.user.host}")
    private String host;
    @Value("${memcache.user.port}")
    private int port;
    @Value("${memcache.user.poolSize}")
    private int poolSize;
    @Value("${memcache.user.connTimeout}")
    private long connTimeout;
    @Value("${memcache.user.opTimeout}")
    private long opTimeout;

    @Bean(name="userMemcacheClient")
    public MemcachedClient getMemcacheClient() throws IOException {
        return this.generateMemcacheClient(host, port, poolSize, connTimeout, opTimeout);
    }
}

My yml properties

memcache:
  default:
    host: 127.0.0.1
    port: 11211
    poolSize: 30
    connTimeout: 1000
    opTimeout: 500
  user:
    host: 10.0.0.248
    port: 9101
    poolSize: 30
    connTimeout: 1000
    opTimeout: 500
  note:
    host: 127.0.0.1
    port: 11211
    poolSize: 30
    connTimeout: 1000
    opTimeout: 500

@Service
public class UserServiceImpl implements UserService{

    @Autowired
    private UserRepository userRepository;

    @Resource
    private MemcachedClient userMemcacheClient;

    @Override
    public User getById(String userId){
        User user = userRepository.findOne(new ObjectId(userId));
        return user;
    }

    @Override
    public String getUserIdBySid(String sid) {
        System.out.println(sid);
        if(StringUtils.isEmpty(sid)) {
            return null;
        }
        String key = String.format(MemcacheKeys.userIdBySid, sid);
        try {
            System.out.println(key);
            String userId = userMemcacheClient.get(key);
            System.out.println(userId);
            if(StringUtils.isEmpty(userId)){
                User user = userRepository.findBySession(sid);
                if(user != null){
                    userId = user.getId().toString();
                    userMemcacheClient.set(key, 100000, userId);
                }
            }
            return userId;
        } catch (InterruptedException e1){
            System.out.println("InterruptedException: " + e1.getMessage());
        } catch (MemcachedException e2){
            System.out.println("MemcachedException: " + e2.getMessage());
        }catch (TimeoutException e3){
            System.out.println("TimeoutException: " + e3.getMessage());
        }
        return null;
    }

}

I use getUserIdBySid with same sid, but sometimes return null.

[killme2008]

Maybe it's evicted by memcached LRU, it's not an issue in xmemcached, if you found this happens, you can telnet to memcached and run get <key> command to test if the item is exists on memcached.

[sunchuanleihit]

I use tencent cmem, cmem doesn`t support version command. Then the heartbeat will fail.
client.setEnableHeartBeat(false) can solve this problem.