How To Troubleshoot Issues in Redis
Redis is an open-source, in-memory key-value data store. It comes with several commands that can help with troubleshooting and debugging issues. Because of Redis’s nature as an in-memory key-value store, many of these commands focus on memory management, but there are others that are valuable for providing an overview of the state of your Redis server. This tutorial will provide details on how to use some of these commands to help diagnose and resolve issues you may run into as you use Redis.
How To Use This Guide
This guide is written as a cheat sheet with self-contained examples. We encourage you to jump to any section that is relevant to the task you’re trying to complete.
The commands shown in this guide were tested on an Ubuntu 18.04 server running Redis version 4.0.9. To set up a similar environment, you can follow Step 1 of our guide on How To Install and Secure Redis on Ubuntu 18.04. We will demonstrate how these commands behave by running them with
redis-cli, the Redis command line interface. Note that if you’re using a different Redis interface — Redli, for example — the exact output of certain commands may differ.
Alternatively, you could provision a managed Redis database instance to test these commands, but note that depending on the level of control allowed by your database provider, some commands in this guide may not work as described. To provision a DigitalOcean Managed Database, follow our Managed Databases product documentation. Then, you must either install Redli or set up a TLS tunnel in order to connect to the Managed Database over TLS.
Troubleshooting Memory-related Issues
memory usage tells you how much memory is currently being used by a single key. It takes the name of a key as an argument and outputs the number of bytes it uses:
- memory usage key_meaningOfLife
For a more general understanding of how your Redis server is using memory, you can run the
memory stats command:
- memory stats
This command outputs an array of memory-related metrics and their values. The following are the metrics reported by
peak.allocated: The peak number of bytes consumed by Redis
total.allocated: The total number of bytes allocated by Redis
startup.allocated: The initial number of bytes consumed by Redis at startup
replication.backlog: The size of the replication backlog, in bytes
clients.slaves: The total size of all replica overheads (the output and query buffers and connection contexts)
clients.normal: The total size of all client overheads
aof.buffer: The total size of the current and rewrite append-only file buffers
db.0: The overheads of the main and expiry dictionaries for each database in use on the server, reported in bytes
overhead.total: The sum of all overheads used to manage Redis’s keyspace
keys.count: The total number of keys stored in all the databases on the server
keys.bytes-per-key: The ratio of the server’s net memory usage and
dataset.bytes: The size of the dataset, in bytes
dataset.percentage: The percentage of Redis’s net memory usage taken by
peak.percentage: The percentage of
peak.allocatedtaken out of
fragmentation: The ratio of the amount of memory currently in use divided by the physical memory Redis is actually using
memory malloc-stats provides an internal statistics report from jemalloc, the memory allocator used by Redis on Linux systems:
- memory malloc-stats
If it seems like you’re running into memory-related issues, but parsing the output of the previous commands proves to be unhelpful, you can try running
- memory doctor
This feature will output any memory consumption issues that it can find and suggest potential solutions.
Getting General Information about Your Redis Instance
A debugging command that isn’t directly related to memory management is
monitor. This command allows you to see a constant stream of every command processed by the Redis server:
OutputOK 1566157213.896437 [0 127.0.0.1:47740] "auth" "foobared" 1566157215.870306 [0 127.0.0.1:47740] "set" "key_1" "878"
Another command useful for debugging is
info, which returns several blocks of information and statistics about the server:
Output# Server redis_version:4.0.9 redis_git_sha1:00000000 redis_git_dirty:0 redis_build_id:9435c3c2879311f3 redis_mode:standalone os:Linux 4.15.0-52-generic x86_64 . . .
This command returns a lot of information. If you only want to see one info block, you can specify it as an argument to
- info CPU
Output# CPU used_cpu_sys:173.16 used_cpu_user:70.89 used_cpu_sys_children:0.01 used_cpu_user_children:0.04
Note that the information returned by the
info command will depend on which version of Redis you’re using.
keys command is helpful in cases where you’ve forgotten the name of a key, or perhaps you’ve created one but accidentally misspelled its name.
keys looks for keys that match a pattern:
- keys pattern
The following glob-style variables are supported
?is a wildcard standing for any single character, so
*is a wildcard that stands for any number of characters, including no characters at all, so
- You can specify two or more characters that the pattern can include by wrapping them in brackets, so
simmy, but not
- To set a wildcard that disregards one or more letters, wrap them in brackets and precede them with a carrot (
sxmmy, but not
- To set a wildcard that includes a range of letters, separate the beginning and end of the range with a hyphen and wrap it in brackets, so
sommy, but not
Warning: The Redis documentation warns that
keys should almost never be used in a production environment, since it can have a major negative impact on performance.
This guide details a number of commands that are helpful for troubleshooting and resolving issues one might encounter as they work with Redis. If there are other related commands, arguments, or procedures you’d like to see outlined in this guide, please ask or make suggestions in the comments below.
For more information on Redis commands, see our tutorial series on How to Manage a Redis Database.