presto-redis/src/main/java/io/prestosql/plugin/redis/RedisRecordCursor.java/RedisRecordCursor/fetchData
class RedisRecordCursor:    private boolean fetchData(String keyString)
    {
        valueString = null;
        valueMap = null;
        // Redis connector supports two types of Redis
        // values: STRING and HASH
        // HASH types requires hash row decoder to
        // fill in the columns
        // whereas for the STRING type decoders are optional
        try (Jedis jedis = jedisPool.getResource()) {
            switch (split.getValueDataType()) {
                case STRING:
                    valueString = jedis.get(keyString);
                    if (valueString == null) {
                        log.warn("Redis data modified while query was running, string value at key %s deleted", keyString);
                        return false;
                    }
                    break;
                case HASH:
                    valueMap = jedis.hgetAll(keyString);
                    if (valueMap == null) {
                        log.warn("Redis data modified while query was running, hash value at key %s deleted", keyString);
                        return false;
                    }
                    break;
                default:
                    log.debug("Redis type for key %s is unsupported", keyString);
                    return false;
            }
        }
        return true;
    }