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Table of contents
1.
Introduction
2.
Redis
3.
Problems in Redis along with Troubleshooting
3.1.
Latency Issues
4.
Experiencing crashes
5.
The following is a list of known Linux problems that affect Redis.
6.
Frequently asked questions
7.
Conclusion
Last Updated: Mar 27, 2024
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Troubleshooting

Author Saksham Gupta
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Introduction

DBMS form the backbone of any coding interview. Thus it's very important to have a good grasp of this topic. But don't you worry about any of it. Ninjas are here for you, and today we will be going to discuss ‘Troubleshooting in Redis’ 

Redis

Redis is an in-memory data structure store that can be used as a distributed, in-memory key-value database, cache, and message broker. Strings, lists, maps, sets, sorted sets, HyperLogLogs, bitmaps, streams, and spatial indices are among the abstract data structures supported by Redis.

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Problems in Redis along with Troubleshooting

Latency Issues

In this context, latency refers to the period between when a client gives a command and when the client receives the command's response. Redis processing times are typically in the sub-microsecond range. However, certain circumstances can result in greater latency statistics. If you're having latency issues, you probably know how to measure them in the context of your application, or your latency issue is visible even at a macro level. Redis-cli, on the other hand, may be used to monitor the latency of a Redis server in milliseconds:

redis-cli --latency -h `host` -p `port`


Redis has latency monitoring features, which can sample several execution pathways to figure out where the server is stalling. This makes debugging the issues described in this guide much easier. Thus we recommend setting latency monitoring as soon as possible. Please see the documentation for the Latency Monitor.

While the latency monitoring sampling and reporting capabilities will make it easier to identify the source of latency in your Redis system, you should still study this material thoroughly to gain a better understanding of Redis and latency spikes.

As a result, even if Redis executes most commands in the sub-microsecond range, a client making a lot of roundtrips to the server will have to pay for network and system latencies.

As a result, an efficient client will strive to reduce the number of roundtrips by pipelining many commands together. The servers and the majority of clients fully support this. MSET/MGET and other grouped commands can also be used for this. Variadic parameters for all data types are now supported by a variety of commands starting with Redis 2.4. 

Here are some pointers:

  • If you can afford it, host the server on a physical machine rather than a virtual one.
     
  • Do not connect/disconnect to the server on a regular basis (especially true for web based applications). Maintain your relationships for as long as feasible.
     
  • Use Unix domain sockets if your client and server are on the same machine.
     
  • Pipelining should be avoided in favor of aggregated commands (MSET/MGET) or commands with variable parameters (if possible).
     
  • If at all possible, choose to pipeline to a series of roundtrips.
     
  • To accommodate scenarios where raw pipelining isn't appropriate, Redis enables Lua server-side scripting (for instance, when the result of a command is an input for the following commands).

Experiencing crashes

When Redis fails, it generates a thorough report of what went wrong. However, looking at the crash report isn't always enough, and the Redis core team can't always reproduce the problem on its own. In this case, we'll require assistance from a user who can reproduce the problem.

This post will show you how to use GDB to give the Redis developers the information they need to track the bug more easily.

The -O2 parameter is used by default when compiling Redis, which means compiler optimizations are enabled. This speeds up the Redis executable, but it also makes Redis (and any other program) more difficult to analyze with GDB. 

It's preferable to use the make no-opt command to attach GDB to Redis that hasn't been optimized (instead of just using the plain make command). However, if you already have a Redis server up and running, there's no need to recompile and restart it unless it causes you trouble. GDB continues to work with executables that have been optimized.

You shouldn't be too concerned about the performance reduction caused by compiling Redis without optimizations.

The following is a list of known Linux problems that affect Redis.

Ubuntu 10.04 and 10.10 (particularly 10.10) have major problems that cause slowdowns if not outright instance hangs. Please avoid using the default kernels that come with these distributions. Both problems have been reported numerous times in the context of EC2 instances, but additional users have confirmed that they also affect native servers (at least by one of the two).

fork() system call performance is known to be poor in several versions of the Xen hypervisor.

Frequently asked questions

  1. What is a Redis?
    Redis is an in-memory data structure store that can be used as a distributed, in-memory key-value database, cache, and message broker. Strings, lists, maps, sets, sorted sets, HyperLogLogs, bitmaps, streams, and spatial indices are among the abstract data structures supported by Redis.
     
  2. What is TLS?
    The successor to SSL, Transport Layer Security (TLS), preserves the secrecy of data transferred between apps and Redis databases. TLS encrypts communications between Redis Enterprise Software nodes as well.
     
  3. What are the disadvantages of Redis
    Clients connecting to the Redis cluster should be aware of the cluster topology, causing overhead configuration on Clients because data is sharded based on the hash slots allotted to each Master. If the master does not have at least one slave, failover does not occur.
     
  4. How is data stored in Redis?
    Data is saved in memory because Redis is an in-memory database (or RAM). All data stored on a server is lost if it crashes. For the data on the disc, Redis has backup procedures in place. When the server reboots, the data is loaded from the disc into memory in this manner.
     
  5. Are there any other Data Structures and Algorithms content in Coding Ninjas Studio?
    Yes, Coding Ninjas Studio allows you to practice coding as well as answer frequently asked interview questions. The more we practice, the more likely we are to acquire a job at our dream company.

Conclusion

In this article, we have extensively discussed the ‘Troubleshooting in Redis’. We hope that this blog has helped you enhance your knowledge of ‘Troubleshooting’ and if you would like to learn more, check out our articles on our Library where you can find everything about DatabasesSQL Probelms, Interview Experiences and other guided paths. Do upvote our blog to help other ninjas grow. Happy Coding!

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