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Using the command line to check redis health

4 ​​min

Dieser Blogartikel ist älter als 5 Jahre – die genannten Inhalte sind eventuell überholt.

In the forth entry of our series on redis we’ll have a look at its CLI tools. The central question for today: How can we check that redis is working as expected using the command line?

redis-CLI basics

Using redis-cli to check database health sounds easy and, in fact, it is: A simple redis-cli PING on the Redis host returns a PONG. This does not look very reliable, but it is. A redis that returns a PONG is fully functional and works as expected.

To go a bit more into detail: it means that the dataset is completely loaded, and Redis is ready for connections. If something does not work fine, it will display error messages such as “(error) LOADING Redis is loading the dataset in memory“. This will return while loading the rdb/aof file or waiting for replication to be completed.

By using the redis-CLI you can easily use the info command and sub-commands to get some more stats and information.

List of commands

redis-cli infoComplete info about the redis-instance
redis-cli info serverServer Information, cersions, configs, binary
redis-cli info clientsConnected clients
redis-cli info memoryStatistics about memory usage and limits
redis-cli info persistenceInfo about RDB and AOF
redis-cli info statsConnection, network, keyspace statistics
redis-cli info replicationReplication settings and status
redis-cli info cpuCPU utilization
redis-cli info clusterCluster settings and status
redis-cli info keyspaceDisplay dbs and number of keys

To repeat commands you can easily use two options for monitoring: redis-cli -r 5 -i 2 <command> will execute the <command> five times with an interval of two seconds.

With these commands you can easily integrate redis in your monitoring. Just add the redis-CLI commands as custom parameters, e.g. to Zabbix or Nagios. You can also use prometheus exporters to get metrics out of your redis.

Integrated latency monitoring, reporting, slow-logs

Maybe some of you ask yourselves why we need monitoring in the first place, as redis is so incredibly fast. The answer is: you’re right, redis is designed to serve a large amount of queries per second per instance. But unfortunately in most applications there is a strict requirement for the average response time and for a worst case latency.

Nevertheless redis has a huge amount of commands, some commands are fast and run in constant or logarithmic time, other commands are slower, possibly causing latency spikes. Other reasons for this way of monitoring are interaction with the operating system (e.g. disk persistence) and the single-thread architecture of redis.

Since version 2.8.13 latency monitoring helps to troubleshoot possible latency problems. The following mechanics are part of this framework:

  • Latency hooks that sample different latency sensitive code paths.
  • Time series recording of latency spikes split by another event.
  • Reporting engine to fetch raw data from the time series.
  • Analysis engine to provide human readable reports and hints according to the measurements.

How to enable latency monitoring?

During runtime of redis latency monitoring can be easily enabled by config set latency-monitor-threshold 100. The tailing number defines a time in milliseconds. In our example, every event that will take more then 100ms will be logged as a latency spike. Here are some commands to display and reset logged events:

latency latestdisplay the latest latency events logged
latency history event-namedisplay up to 160 elements for the given event name, you get timestamp and latency value
latency resetreset all events at the time-series
latency reset event-namereset only the given event-name
latency graph event-nameascii-art style graph for the event
latency doctorgives details information about latency spikes and advices

What should I do when redis experiences latency spikes?

The next step could be to enable the slow-log. With config set slowlog-log-slower-than 1000 you can log every event that lasts longer then 1000ms. More commands:

slowlog-log-slower-than -1disable slow log
slowlog-log-slower-than 0log every command
slowlog-max-len Nmaximum length of the logfile (ringbuffer-style)
slowlog get Nwill display the last N events in the log
slowlog lenlength of the current logfile
slowlog resetdelete all information at the log

More on redis

We’ve already published various articles on redis. If you’re new to the subject you best start with our introduction. Have your redis up and running? Learn how to back its data up and save snapshots. Finally, we show you how to make your data highly available with redis.

Read on

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2 Kommentare

  1. Redis has great cli tool to mange it or get stats how it’s running but no matter if you will use gui or just a command line it needs to be monitored. I recently wrote an article how to monitor Redis for free and get notifications when needed, you can see it here, if interested:

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