When we run the redis-benchmark, the “error from server moved” shows one or more of the keys used in the benchmark are moving to a different cluster node. Read the article to know more about the error and its troubleshooting. At Bobcares, with our Server Management Service, we can handle your issues.

Overview

1. Knowing more about “Error from server moved” in Redis-Benchmark
2. Error from Server Moved in Redis-Benchmark-A Sample
3. Error Causes
4. Error Fixes
5. Important Considerations

Knowing more about “Error from server moved” in Redis-Benchmark

A hash slot method is used in a Redis Cluster to distribute data among many nodes. Every key is associated with a distinct hash slot, and every hash slot is linked to a distinct cluster node.

When using Redis Cluster and a client tries to access data that is located on a different node than the one it first connected to, Redis will throw the “MOVED” error. Each key in the Redis Cluster architecture has a designated slot, and the specific architecture spreads data over many servers. The node verifies that a key is in its designated slots when a client attempts to access it. In the event that it doesn’t, the client should resend the request to the appropriate node because it will respond with a “MOVED” error.

Key Points:

1. Slot and Key Assignment:
   • Data is divided into 16,384 slots by Redis Cluster.
   • A portion of these slots are the responsibility of each cluster node.
   • A hash function maps slots with keys.
2. MOVED Error:
   • The client is informed by this error that the requested key is not present on the current node.
   • The address (host and port) of the node holding the data as well as the correct slot are included in the message.
3. Handling the MOVED Error:
   • In order to handle this issue, clients must be able to reroute the request to the appropriate node.
   • Redis Cluster is supported by many Redis clients, and the MOVED issue is handled automatically.
4. Benchmarking with redis-benchmark:
   • If redis-benchmark is not cluster-aware or is not set up properly to follow redirection, we may get the MOVED error while using it with a Redis cluster.
   • Verify that the benchmarking tool is compatible with cluster mode, or indicate which node to test against.

Error from Server Moved in Redis-Benchmark-A Sample

An example of the error is the following:

This message means that the key belonging to hash slot 12182 has been moved to the node at 127.0.0.1:7002.

Error Causes

1. When we run redis-benchmark on a single Redis node in a cluster, we may see MOVED errors because the keys are spread across multiple nodes.

2. Keys are hashed to slots, and during cluster rebalancing or initial setup, they might be moved to different nodes.

3. Clients connecting directly to a node without considering slot ownership may face MOVED errors when the node doesn’t own the required slot.

4. Network problems may lead to incomplete requests or inaccurate node targeting, causing MOVED errors as the request doesn’t reach the correct node.

5. Using an outdated version of Redis or redis-benchmark can lead to issues, as they may lack full support for cluster features.

Error Fixes

1. Use Cluster-Aware Tools: We can use tools like memtier_benchmark instead of redis-benchmark for cluster-aware testing.

2. Connect to a Proxy: Also, use proxies such as Twemproxy (Nutcracker) or Redis Cluster Proxy to manage redirection and cluster awareness.

3. Enable Cluster Mode: Use the -c option in redis-benchmark to enable cluster mode, allowing it to handle redirects.

4. Check Redis Cluster Status: We can run redis-cli cluster info to verify the health of the Redis cluster and ensure no ongoing resharding or node failures.

5. Verify Node Configuration: Ensure Redis nodes configuration are proper as part of the cluster.

6. Update redis-benchmark: Use the latest version of redis-benchmark to avoid limitations with Redis clusters.

7. Client Configuration: We can use a Redis client library that supports Redis Cluster and can handle this errors automatically. Some examples include Jedis for Java, redis-py-cluster for Python, and ioredis for Node.js.

8. Correct Node Addressing: Ensure the application connects to the cluster using a known node, but be ready to redirect requests as instructed by the MOVED response.

9. Manual Testing: If necessary, manually issue commands to the specified node in the MOVED response to verify connectivity.

Important Considerations

1. Redis Cluster reassigns slots and promotes replicas in order to handle node failures.

2. During failover, clients should be ready for brief interruptions.

3. Maintaining maximum performance and dependability requires regular monitoring and management of the Redis Cluster.

4. To manage and debug cluster issues, use redis-cli with the –cluster parameters.

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Conclusion

Using cluster-aware methods and tools is key to benchmarking a Redis cluster successfully. Memtier_benchmark and redis-benchmark with the -c option are examples of cluster-enabled benchmarking tools that we may use to reliably assess performance without running into MOVED problems. Furthermore, cluster stability and performance may be preserved by employing proxies and making sure the Redis nodes are setup appropriately and kept up to date. To ensure peak performance, always check the health of the cluster and make changes as necessary.

To sum up, our Support team went over the details of error from server moved in redis-benchmark, along with its causes and solutions. We’ve also included the important considerations to take while troubleshootng this error. We may make sure the application communicates with the cluster effectively by being aware of how Redis Cluster functions and responding to the MOVED error correctly.