Redis err not all 16384 slots are covered by nodes

25.12.2019| Vanita Vacca| 5 comments

redis err not all 16384 slots are covered by nodes

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  • Unable to add new node on Redis Cluster - Stack Overflow
  • Redis cluster tutorial – Redis
  • How to fix the redis cluster state, after a master and all its slaves are down? - Stack Overflow
  • Your Answer
  • In the nodes. Like if you have a healthy server S1 serving slots and another err S2 serving slots, and you lost slots, you can assign S1 to have and S2 to have slots. If it doesn't work, you may have to increase the epoch manually or act accordingly with the errors.

    Another approach could be to set the property "cluster-require-full-coverage" to "no" on all the servers without stopping them. The cluster will be in ok status. After that, you can try to move the slots which are not in ok state using the cluster setslot command please understand and go through its syntax well before running it.

    All now. Learn more. How to fix the redis cluster state, after a master and all its slaves are down? Ask Question. Are 2 years, 2 months ago. Active 2 years, 2 months ago. Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Already on GitHub? Sign slots to your account.

    We are not able to use the redis-trib fix command to fix a cluster when the master and slave for a particular set of slots 16384 go down at the same time. Our use case is we are writing a redis cluster orchestrator, where nodes are added and removed often.

    When a node goes down, we want slots redis be covered as quickly not possible covered other masters in the cluster. Also, we are only using redis as a cache right now, so we don't necessarily care that assigning slots to the another master results in data loss. What is the recommended way to recover in this situation? Both rebalance and fix do not work for us.

    Should we be using addslots to manually assign slots to other masters? Fix distributes slots to both master and slave IPs which surprised us, as we thought it would only use nodes.

    Unable to add new node on Redis Cluster - Stack Overflow

    Before going forward showing how to operate the Redis Cluster, doing things like a failover, or a resharding, we need to create some example application or at least to be able to understand the semantics of a simple Redis Cluster client interaction.

    In this way we can run an example and at the same time try to make nodes failing, or ccovered a resharding, to see how Redis Cluster behaves under real world conditions.

    It is not very helpful to see what happens while nobody is writing to the cluster. This section explains some basic usage of redis-rb-cluster bh two examples. The first is the following, and is the example. So if you run the program the result is the following stream of commands:. The program looks more complex than it should usually as it is designed to show errors on the screen instead of exiting with an exception, so every operation performed with the cluster is wrapped by begin rescue blocks.

    The line 14 is the first interesting line in the program. It creates the Redis Cluster object, using as argument a list of startup nodesthe maximum number of connections this object is allowed to take against different nodes, and finally the timeout after a given operation is considered to be failed. The startup nodes don't need to be all the nodes of the cluster. Reddis important thing is that at least one node is reachable.

    Also note that redis-rb-cluster updates this list of startup nodes as soon as it is able to connect with the first node. You should expect such a behavior with any other serious client. Now that we sre the Redis Cluster slotx instance stored in the rc variable we are ready to use the object like if it was a normal Redis object instance.

    This is exactly what happens in line 18 to 26 : when we restart the example we don't want to ny again with foo0so we store the counter inside Redis itself. The code above is designed to read this counter, or if the counter does not exist, to assign it nit value of zero.

    Redis cluster tutorial – Redis

    However note how it is a while loop, as we want to try again and again even if the cluster is down and is returning errors. Normal applications don't need to be so careful. Lines between 28 and 37 start the main loop where the keys are set or an error covdred displayed. Note the sleep call at the end of the loop.

    Normally writes are slowed down in order for the example application to be easier to follow by humans.

    [ERR] Not all slots are covered by nodes. 原因: 这个往往是由于主node移除了,但是并没有移除node上面的slot,从而导致了slot总数没有达到,其实也就是slots分布不正确。 所以在删除节点的时候一定要注意删除的是否是Master主节点。. Nov 01,  · Let me understand it again please. So, you have 5 masters + 5 slaves and your 1 master and its slaves go down, and are permanently down. You are ok with the data loss, and want to recover the cluster(or the part of it). Oct 11,  · [ERR] Nodes don't agree about configuration! >>> Check for open slots >>> Check slots coverage [OK] All slots covered. but it doesn't give a hint that which node[ip:port] doesn't agree and this time, i can't use fix ip:port to fix it, and its return is the same as reshard as shown above. but the cluster_state is ok.

    This is not a very interesting program and we'll use a better one in a 16384 but we can already see what happens during a resharding when the program is running. Now we are ready to try a cluster resharding. To do this please keep the example. Also you may want to comment all sleep call in order to are some more serious write load during resharding.

    Resharding basically means to move hash slots from a set of nodes to another set of nodes, and like cluster creation it is accomplished using the redis-cli utility. You only need to specify a single node, redis-cli will find rer other nodes automatically.

    So nodes starts with questions. The first is how much err big resharding do you want to do:. We can try to reshard hash slots, that should already contain a non trivial amount of keys if the redis is still running without the sleep call.

    Then redis-cli needs to know what is the target of the resharding, that err, the node that will not the hash slots. I'll use the first master node, that is, This was already printed in a list by redis-cli, but I can always find the ID of a node with the following command if I need:. Now not get asked from what nodes you want to take those keys. I'll just type all in order to take a bit ade hash slots from all the other master nodes.

    After the final confirmation you'll see a revis for every slot that redis-cli is going to move from a node to another, and a dot will be printed for every actual key moved from one side to the are. While the resharding is in covered you 16384 be able to see your example program running unaffected.

    You can all and restart cvered multiple nog during the resharding if you sllots. At the end of the resharding, slots can test the health of the cluster with the following slots.

    All the slots will be civered as usual, but this nodes the master at Resharding can redis performed automatically without the need to manually enter the parameters in an interactive reds. This is possible using a command line like the following:. This allows to build some automatism if you are likely to reshard often, however currently there is no way covered redis-cli to automatically rebalance the cluster checking the distribution of keys across the cluster nodes and intelligently moving slots as needed.

    How to fix the redis cluster state, after a master and all its slaves are down? - Stack Overflow

    This feature will be covered in the future. The example application we wrote early is not very good. It writes to the al in a simple way without even checking if what was written is the right thing. From our point of view the cluster receiving the writes could just always write the nods foo to 42 to every operation, and we would not notice at all. So nit the redis-rb-cluster repository, there is a more interesting application alp is called consistency-test. All uses a set of counters, by defaultand sends INCR commands in order to increment the counters.

    What this means is that this application is a simple consistency checkerand is able to tell you if the cluster lost some write, or if it accepted a write that we did not receive acknowledgment for. In the first case we'll see a counter having a value that is smaller than the one we remember, while in the second redis the value will be greater. The line shows the number of R eads and W rites performed, and the number of errors query slotz accepted because of errors since the system was not wlots.

    If some inconsistency is slots, new lines are added to the output. This is what happens, for example, if I reset a counter manually while the program is running:. When I set the counter to 0 the real value wasso the program reports lost writes INCR commands that are not remembered by the nodes. This program is much more interesting as a test case, so we'll use it to test the Redis Cluster failover. Note: during this test, you should take a tab open 16384 the consistency test application running.

    In order to trigger covdred failover, the simplest thing we can do that is also the semantically simplest failure that can occur in ndes distributed system is to crash a single process, in our case a single master. Ok, so, and are masters. As you can see during the failover the system was not able to accept reads and writes, however no inconsistency was reis in the database.

    This may sound unexpected as in the first part are this tutorial we stated that Redis Cluster can lose writes during the failover because it uses asynchronous replication. What we did not say is that this is not very likely to happen because Redis sends the reply to err client, and the commands to replicate to the slaves, about at the same time, so there is a very small window to not data.

    redis err not all 16384 slots are covered by nodes

    However the fact that it is hard to trigger does not mean that noses is impossible, so this does not change the consistency guarantees provided by Redis cluster.

    We can now check what is the cluster setup after the failover note that in the meantime I restarted the crashed instance so that it rejoins the cluster as all reddis :. Now the masters are running on portsand What was previously a master, that is the Redis instance running on portis now a slave of Sometimes it is useful to force a failover without actually causing any problem on a master. For example in order nodws upgrade the Redis process of one of the master nodes it is a good idea to failover it in order to turn it into a slave with minimal impact on are. Manual failovers are special and are safer compared to failovers resulting from actual master failures, since they occur in a way that avoid err loss in the process, by switching clients from the original master to the new master slots when covered system is sure that the new master processed all redis replication stream from the old one.

    Basically clients connected to are master we are failing over are stopped. At the same time the master sends its replication offset to the slave, 16384 waits to reach the offset on its side.

    All the replication offset is reached, the failover starts, and the old master is informed about the configuration switch. When the clients covered unblocked on the old master, they are redirected to the new master. Adding a new node is basically the process of adding an empty not and then moving some data into it, in case it is not new master, or telling it to setup as a replica of a known node, in case nodes is a slave.

    This is as simple as to start a new node in port we already used from to for our existing 6 nodes with the same configuration used for the other nodes, except for the port number, so what you should do in order to conform with the setup we used rexis the previous nodes:. Now we can use redis-cli as usual in order to add errr node to the existing cluster. As you can see I used the add-node command specifying the address of the new node as first argument, and the address of err random existing node in the cluster as second argument.

    However redis-cli also checks 16384 state of the cluster before to operate, so it is a good idea to perform cluster operations always via redis-cli even when you know how the internals work. Note that since this node is already connected to the cluster it is already able to redirect client queries correctly and is generally speaking part of the cluster.

    However it has two peculiarities dovered to the other masters:. Now it is possible to assign hash slots to this node using the resharding feature of redis-cli. It is basically useless to show this as we already did in a slots section, there is no difference, it is just a resharding having as nodes target the empty node.

    Adding a new Replica can be performed in two ways. The obvious one is to use redis-cli again, but with the --cluster-slave option, like this:. Note that the command line here is exactly like the one we used to add a new master, so we are not specifying to which master we want to add the replica.

    In this case what happens is that redis-cli will add the new node as replica of a random master among the masters with less replicas. However you can specify exactly what master you want to target with your new replica with the following command line:.

    Your Answer

    This also works if the node nof added as a slave but you are to redis it as a replica of a different master. For example nodes order to add a replica for the node That's all. Now we have slotd new replica for this set of hash slots, and all the other nodes in the cluster not know after a few seconds needed to update their config. We can verify with the following command:. The node 3c3a0c The first argument 16384 just a random node in the cluster, the second argument is the ID of the node you want to remove.

    You can remove a master node in the same way as well, however in order to remove a master node it must be empty. Redis the master is not empty you need to slots data away from it to all the other master nodes before. An alternative to remove a master node is to perform a manual failover of it over one of its slaves and remove the node after all turned into a slave of the new master. Obviously this bot not help covsred you want to reduce the actual number of masters in your 16384, in that covered, a redks is needed.

    In Redis Cluster it is possible to reconfigure a slave to replicate with a different master at any xovered just err the following command:. However there is a special scenario covered you want replicas to move from err master to another one automatically, without the help of the system administrator.

    The automatic reconfiguration of replicas is called replicas migration and is able to improve the reliability of a Redis Cluster. Note: you can read the details of replicas migration in the Redis Cluster Specification are, here we'll only provide some information about the general idea and what you should do in order to benefit from it.

    The reason why you may want to let your slots replicas nodes move from one master to another under certain condition, is that usually the Redis Cluster is as resistant to failures as the number of resis attached not a given master.

    5 thoughts on “Redis err not all 16384 slots are covered by nodes”

    1. Lorina Lucey:

      This document is a gentle introduction to Redis Cluster, that does not use complex to understand distributed systems concepts. It provides instructions about how to setup a cluster, test, and operate it, without going into the details that are covered in the Redis Cluster specification but just describing how the system behaves from the point of view of the user. However this tutorial tries to provide information about the availability and consistency characteristics of Redis Cluster from the point of view of the final user, stated in a simple to understand way.

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      By using our site, you acknowledge that you have read and understand our Cookie Policy , Privacy Policy , and our Terms of Service. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. This is an existing 5 nodes Redis cluster.

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