淘淘商城第38讲——使用Jedis操作集群版Redis时，报错：redis.clients.jedis.exceptions.JedisClusterMaxRedirectionsException

- 日理万妓 2023-02-28 01:43 4阅读 0赞

# 问题描述 #

今天碰到一个问题，那就是在使用Jedis操作集群版Redis时，报了一个如下这样一个错误，具体错误信息记录如下：

redis.clients.jedis.exceptions.JedisClusterMaxRedirectionsException: Too many Cluster redirections?
    	at redis.clients.jedis.JedisClusterCommand.runWithRetries(JedisClusterCommand.java:34)
    	at redis.clients.jedis.JedisClusterCommand.runWithRetries(JedisClusterCommand.java:67)
    	at redis.clients.jedis.JedisClusterCommand.runWithRetries(JedisClusterCommand.java:83)
    	at redis.clients.jedis.JedisClusterCommand.runWithRetries(JedisClusterCommand.java:67)
    	at redis.clients.jedis.JedisClusterCommand.runWithRetries(JedisClusterCommand.java:83)
    	at redis.clients.jedis.JedisClusterCommand.runWithRetries(JedisClusterCommand.java:67)
    	at redis.clients.jedis.JedisClusterCommand.run(JedisClusterCommand.java:29)
    	at redis.clients.jedis.JedisCluster.get(JedisCluster.java:91)
    	at com.taotao.test.jedis.JedisTest.testJedisCluster(JedisTest.java:61)

下面我给出了我的测试代码，你能看懂我写的啥吗？  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3llcmVueXVhbl9wa3U_size_16_color_FFFFFF_t_70]  
这里，我还得说明一点，我使用的Redis是`redis-3.2.3.tar.gz`这个版本，使用的Jedis是`jedis-2.7.2.jar`这个版本。

# 报错原因 #

报了这个异常之后，我试图想找到报错原因，于是我在网上找了好多的文章。终于，皇天不负有心人，这个报错原因我想我是给找出来了。这还得从Jedis的源码说起。

先从Jedis的源码中找到这个异常，这个异常是在JedisClusterCommand类中，如下所示。

if (redirections <= 0) { 
        throw new JedisClusterMaxRedirectionsException("Too many Cluster redirections? key=" + key);
    }

当我们在使用Jedis操作集群版Redis时，会使用到JedisCluster类，该类中所有API的调用方式都类似下面这样：

public String set(final String key, final String value) { 
        return new JedisClusterCommand<String>(connectionHandler, maxRedirections) { 
            @Override
            public String execute(Jedis connection) { 
                return connection.set(key, value);
            }
        }.run(key);
    }

所以咱们要分析的重点代码应该在JedisClusterCommand这个类里，重要代码如下：

public T run(int keyCount, String... keys) { 
        if (keys == null || keys.length == 0) { 
            throw new JedisClusterException("No way to dispatch this command to Redis Cluster.");
        }
        if (keys.length > 1) { 
            int slot = JedisClusterCRC16.getSlot(keys[0]);
            for (int i = 1; i < keyCount; i++) { 
                int nextSlot = JedisClusterCRC16.getSlot(keys[i]);
                if (slot != nextSlot) { 
                    throw new JedisClusterException("No way to dispatch this command to Redis Cluster "
                            + "because keys have different slots.");
                }
            }
        }
    
        return runWithRetries(SafeEncoder.encode(keys[0]), this.redirections, false, false);
    }
    
    private T runWithRetries(byte[] key, int redirections, boolean tryRandomNode, boolean asking) { 
        // 问题应该出自这里，应该是redirections参数的值小于等于0，才导致抛出了下面这个异常
        if (redirections <= 0) { 
            JedisClusterMaxRedirectionsException exception = new JedisClusterMaxRedirectionsException(
                    "Too many Cluster redirections? key=" + SafeEncoder.encode(key));
            throw exception;
        }
    
        Jedis connection = null;
        try { 
            if (asking) { 
                // TODO: Pipeline asking with the original command to make it
                // faster....
                connection = askConnection.get();
                connection.asking();
    
                // if asking success, reset asking flag
                asking = false;
            } else { 
                if (tryRandomNode) { 
                    connection = connectionHandler.getConnection();
                } else { 
                    connection = connectionHandler.getConnectionFromSlot(JedisClusterCRC16.getSlot(key));
                }
            }
    
            return execute(connection);
        } catch (JedisConnectionException jce) { 
            if (tryRandomNode) { 
                // maybe all connection is down
                throw jce;
            }
    
            // release current connection before recursion
            releaseConnection(connection);
            connection = null;
    
            // retry with random connection
            return runWithRetries(key, redirections - 1, true, asking);
        } catch (JedisRedirectionException jre) { 
            // if MOVED redirection occurred,
            if (jre instanceof JedisMovedDataException) { 
                // it rebuilds cluster's slot cache
                // recommended by Redis cluster specification
                this.connectionHandler.renewSlotCache(connection);
            }
    
            // release current connection before recursion or renewing
            releaseConnection(connection);
            connection = null;
    
            if (jre instanceof JedisAskDataException) { 
                asking = true;
                askConnection.set(this.connectionHandler.getConnectionFromNode(jre.getTargetNode()));
            } else if (jre instanceof JedisMovedDataException) { 
            } else { 
                throw new JedisClusterException(jre);
            }
    
            return runWithRetries(key, redirections - 1, false, asking);
        } finally { 
            releaseConnection(connection);
        }
    }

看了以上runWithRetries方法之后，我们大概是知道报错原因了，就是redirections这个参数搞的鬼！那么redirections参数到底应该怎么理解呢？该参数代表的是节点调转次数，实际上也可以看做是重试次数，也就是说连接集群中某个节点失败后，重连其他节点的次数。

# 解决方案 #

初始化JedisCluster时，设定构造JedisCluster对象的maxRedirections参数，如下图所示。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3llcmVueXVhbl9wa3U_size_16_color_FFFFFF_t_70 1]  
运行以上测试方法，虽然需要等待很长时间，Eclipse控制台才打印出结果，但是没有报**其他连接重试次数太多**的异常了。

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3llcmVueXVhbl9wa3U_size_16_color_FFFFFF_t_70]: /images/20230209/890094d0ad3848069b9f4681732c58f0.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3llcmVueXVhbl9wa3U_size_16_color_FFFFFF_t_70 1]: /images/20230209/57010d21443e4c95bb0274270246ac9f.png