keydb-cli is the keydb command line interface, a simple program that allows
to send commands to keydb, and read the replies sent by the server, directly
from the terminal.
It has two main modes: an interactive mode where there is a REPL (Read
Eval Print Loop) where the user types commands and get replies; and another
mode where the command is sent as arguments of
keydb-cli, executed, and
printed on the standard output.
In interactive mode,
keydb-cli has basic line editing capabilities to provide
a good typing experience.
keydb-cli is not just that. There are options you can use to launch
the program in order to put it into special modes, so that
definitely do more complex tasks, like simulate a replica and print the
replication stream it receives from the master, check the latency of a keydb
server and show statistics or even an ASCII-art spectrogram of latency
samples and frequencies, and many other things.
This guide will cover the different aspects of
keydb-cli, starting from the
simplest and ending with the more advanced ones.
If you are going to use keydb extensively, or if you already do, chances are
you happen to use
keydb-cli a lot. Spending some time to familiarize with
it is likely a very good idea, you'll see that you'll work more effectively
with keydb once you know all the tricks of its command line interface.
To just run a command and have its reply printed on the standard output is as
simple as typing the command to execute as separated arguments of
The reply of the command is "7". Since keydb replies are typed (they can be
strings, arrays, integers, NULL, errors and so forth), you see the type
of the reply between brackets. However that would be not exactly a great idea
when the output of
keydb-cli must be used as input of another command, or when
we want to redirect it into a file.
keydb-cli only shows additional information which improves
readability for humans when it detects the standard output is a tty (a terminal
basically). Otherwise it will auto-enable the raw output mode, like in the
(integer) was omitted from the output since the CLI detected
the output was no longer written to the terminal. You can force raw output
even on the terminal with the
Similarly, you can force human readable output when writing to a file or in
pipe to other commands by using
keydb-cli connects to the server at 127.0.0.1 port 6379.
As you can guess, you can easily change this using command line options.
To specify a different host name or an IP address, use
-h. In order
to set a different port, use
If your instance is password protected, the
-a <password> option will
preform authentication saving the need of explicitly using the
Alternatively, it is possible to provide the password to
keydb-cli via the
REDISCLI_AUTH environment variable.
Finally, it's possible to send a command that operates on a database number
other than the default number zero by using the
-n <dbnum> option:
Some or all of this information can also be provided by using the
option and a valid URI:
keydb-cli uses a plain TCP connection to connect to KeyDB.
You may enable SSL/TLS using the
--tls option, along with
--cacertdir to configure a trusted root certificate bundle or directory.
If the target server requires authentication using a client side certificate,
you can specify a certificate and a corresponding private key using
There are two ways you can use
keydb-cli in order to get the input from other
commands (from the standard input, basically). One is to use as last argument
the payload we read from stdin. For example, in order to set a keydb key
to the content of the file
/etc/services of my computer, I can use the
As you can see in the first line of the above session, the last argument of the
SET command was not specified. The arguments are just
SET foo without the
actual value I want my key to be set to.
-x option was specified and a file was redirected to the CLI's
standard input. So the input was read, and was used as the final argument for
the command. This is useful for scripting.
A different approach is to feed
keydb-cli a sequence of commands written in a
All the commands in
commands.txt are executed one after the other by
keydb-cli as if they were typed by the user interactive. Strings can be
quoted inside the file if needed, so that it's possible to have single
arguments with spaces or newlines or other special chars inside:
It is possible to execute the same command a specified number of times
with a user selected pause between the executions. This is useful in
different contexts, for example when we want to continuously monitor some
key content or
INFO field output, or when we want to simulate some
recurring write event (like pushing a new item into a list every 5 seconds).
This feature is controlled by two options:
-r <count> and
The first states how many times to run a command, the second configures
the delay between the different command calls, in seconds (with the ability
to specify decimal numbers like 0.1 in order to mean 100 milliseconds).
By default the interval (or delay) is set to 0, so commands are just executed ASAP:
To run the same command forever, use
-1 as count.
So, in order to monitor over time the RSS memory size it's possible
to use a command like the following:
Mass insertion of data using
Mass insert using
keydb-cli is covered in a separated page since it's a
worthwhile topic itself. Please refer to our
mass insertion guide.
Sometimes you may want to use
keydb-cli in order to quickly export data from
keydb to an external program. This can be accomplished using the CSV (Comma
Separated Values) output feature:
Currently it's not possible to export the whole DB like that, but only to run single commands with CSV output.
keydb-cli has extensive support for using the new Lua debugging facility
of Lua scripting, available starting with keydb 3.2. For this feature, please
refer to the keydb Lua debugger documentation.
However, even without using the debugger, you can use
run scripts from a file in a way more comfortable way compared to typing
the script interactively into the shell or as an argument:
EVAL command takes the list of keys the script uses, and the
other non key arguments, as different arrays. When calling
provide the number of keys as a number. However with
keydb-cli and using
--eval option above, there is no need to specify the number of keys
explicitly. Instead it uses the convention of separating keys and arguments
with a comma. This is why in the above call you see
foo , bar as arguments.
foo will populate the
KEYS array, and
--eval option is useful when writing simple scripts. For more
complex work, using the Lua debugger is definitely more comfortable. It's
possible to mix the two approaches, since the debugger also uses executing
scripts from an external file.
So far we explored how to use the keydb CLI as a command line program.
This is very useful for scripts and certain types of testing, however most
people will spend the majority of time in
keydb-cli using its interactive
In interactive mode the user types keydb commands at the prompt. The command is sent to the server, processed, and the reply is parsed back and rendered into a simpler form to read.
Nothing special is needed for running the CLI in interactive mode - just lunch it without any arguments and you are in:
127.0.0.1:6379> is the prompt. It reminds you that you are
connected to a given keydb instance.
The prompt changes as the server you are connected to changes, or when you are operating on a database different than the database number zero:
connect command in interactive mode makes it possible to connect
to a different instance, by specifying the hostname and port we want
to connect to:
As you can see the prompt changes accordingly. If the user attempts to connect
to an instance that is unreachable, the
keydb-cli goes into disconnected
mode and attempts to reconnect with each new command:
Generally after a disconnection is detected, the CLI always attempts to reconnect transparently: if the attempt fails, it shows the error and enters the disconnected state. The following is an example of disconnection and reconnection:
When a reconnection is performed,
keydb-cli automatically re-select the
last database number selected. However, all the other state about the
connection is lost, such as the state of a transaction if we
were in the middle of it:
This is usually not an issue when using the CLI in interactive mode for testing, but you should be aware of this limitation.
You can access a history of commands executed, in order to avoid retyping
them again and again, by pressing the arrow keys (up and down).
The history is preserved between restarts of the CLI, in a file called
.keydbcli_history inside the user home directory, as specified
HOME environment variable. It is possible to use a different
history filename by setting the
keydbCLI_HISTFILE environment variable,
and disable it by setting it to
The CLI is also able to perform command names completion by pressing the TAB key, like in the following example:
Once you've typed a KeyDB command name at the prompt, the CLI will display syntax hints. This behavior can be turned on and off via the CLI preferences.
There are two ways to customize the CLI's behavior. The file
in your home directory is loaded by the CLI on startup. You can override the
file's default location by setting the
REDISCLI_RCFILE environment variable to
an alternative path. Preferences can also be set during a CLI session, in which
case they will last only the the duration of the session.
To set preferences, use the special
:set command. The following preferences
can be set, either by typing the command in the CLI or adding it to the
:set hints- enables syntax hints
:set nohints- disables syntax hints
It's possible to run the same command multiple times by prefixing the command name by a number:
keydb has a number of commands and sometimes, as you test things,
you may not remember the exact order of arguments.
keydb-cli provides online
help for most keydb commands, using the
help command. The command can be used
in two forms:
help @<category>shows all the commands about a given category. The categories are:
help <commandname>shows specific help for the command given as argument.
For example in order to show help for the
PFADD command, use:
Summary: Adds the specified elements to the specified HyperLogLog.
help supports TAB completion as well.
clear command in interactive mode clears the terminal's screen.
So far we saw two main modes of
- Command line execution of keydb commands.
- Interactive "REPL-like" usage.
However the CLI performs other auxiliary tasks related to keydb that are explained in the next sections:
- Monitoring tool to show continuous stats about a keydb server.
- Scanning a keydb database for very large keys.
- Key space scanner with pattern matching.
- Acting as a Pub/Sub client to subscribe to channels.
- Monitoring the commands executed into a keydb instance.
- Checking the latency of a keydb server in different ways.
- Checking the scheduler latency of the local computer.
- Transferring RDB backups from a remote keydb server locally.
- Acting as a keydb replica for showing what a replica receives.
- Simulating LRU workloads for showing stats about keys hits.
- A client for the Lua debugger.
This is probably one of the lesser known features of
keydb-cli, and one
very useful in order to monitor keydb instances in real time.
To enable this mode, the
--stat option is used.
The output is very clear about the behavior of the CLI in this mode:
In this mode a new line is printed every second with useful information and the difference between the old data point. You can easily understand what's happening with memory usage, clients connected, and so forth.
-i <interval> option in this case works as a modifier in order to
change the frequency at which new lines are emitted. The default is one
In this special mode,
keydb-cli works as a key space analyzer. It scans the
dataset for big keys, but also provides information about the data types
that the data set consists of. This mode is enabled with the
and produces quite a verbose output:
In the first part of the output, each new key larger than the previous larger key (of the same type) encountered is reported. The summary section provides general stats about the data inside the keydb instance.
The program uses the
SCAN command, so it can be executed against a busy
server without impacting the operations, however the
-i option can be
used in order to throttle the scanning process of the specified fraction
of second for each 100 keys requested. For example,
-i 0.1 will slow down
the program execution a lot, but will also reduce the load on the server
to a tiny amount.
Note that the summary also reports in a cleaner form the biggest keys found for each time. The initial output is just to provide some interesting info ASAP if running against a very large data set.
It is also possible to scan the key space, again in a way that does not
block the keydb server (which does happen when you use a command
KEYS *), and print all the key names, or filter them for specific
patterns. This mode, like the
--bigkeys option, uses the
so keys may be reported multiple times if the dataset is changing, but no
key would ever be missing, if that key was present since the start of the
iteration. Because of the command that it uses this option is called
head -10 is used in order to print only the first lines of the
Scanning is able to use the underlying pattern matching capability of
SCAN command with the
Piping the output through the
wc command can be used to count specific
kind of objects, by key name:
The CLI is able to publish messages in keydb Pub/Sub channels just using
PUBLISH command. This is expected since the
PUBLISH command is very
similar to any other command. Subscribing to channels in order to receive
messages is different - in this case we need to block and wait for
messages, so this is implemented as a special mode in
other special modes this mode is not enabled by using a special option,
but simply by using the
PSUBSCRIBE command, both in
interactive or non interactive mode:
The reading messages message shows that we entered Pub/Sub mode.
When another client publishes some message in some channel, like you
can do using
keydb-cli PUBLISH mychannel mymessage, the CLI in Pub/Sub
mode will show something such as:
This is very useful for debugging Pub/Sub issues.
To exit the Pub/Sub mode just process
Similarly to the Pub/Sub mode, the monitoring mode is entered automatically
once you use the
MONITOR mode. It will print all the commands received
by a keydb instance:
Note that it is possible to use to pipe the output, so you can monitor
for specific patterns using tools such as
keydb is often used in contexts where latency is very critical. Latency involves multiple moving parts within the application, from the client library to the network stack, to the keydb instance itself.
The CLI has multiple facilities for studying the latency of a keydb instance and understanding the latency's maximum, average and distribution.
The basic latency checking tool is the
--latency option. Using this
option the CLI runs a loop where the
PING command is sent to the keydb
instance, and the time to get a reply is measured. This happens 100
times per second, and stats are updated in a real time in the console:
The stats are provided in milliseconds. Usually, the average latency of
a very fast instance tends to be overestimated a bit because of the
latency due to the kernel scheduler of the system running
itself, so the average latency of 0.19 above may easily be 0.01 or less.
However this is usually not a big problem, since we are interested in
events of a few millisecond or more.
Sometimes it is useful to study how the maximum and average latencies
evolve during time. The
--latency-history option is used for that
purpose: it works exactly like
--latency, but every 15 seconds (by
default) a new sampling session is started from scratch:
You can change the sampling sessions' length with the
-i <interval> option.
The most advanced latency study tool, but also a bit harder to
interpret for non experienced users, is the ability to use color terminals
to show a spectrum of latencies. You'll see a colored output that indicates the
different percentages of samples, and different ASCII characters that indicate
different latency figures. This mode is enabled using the
There is another pretty unusual latency tool implemented inside
It does not check the latency of a keydb instance, but the latency of the
computer you are running
keydb-cli on. What latency you may ask?
The latency that's intrinsic to the kernel scheduler, the hypervisor in case
of virtualized instances, and so forth.
We call it intrinsic latency because it's opaque to the programmer, mostly.
If your keydb instance has bad latency regardless of all the obvious things
that may be the source cause, it's worth to check what's the best your system
can do by running
keydb-cli in this special mode directly in the system you
are running keydb servers on.
By measuring the intrinsic latency, you know that this is the baseline,
and keydb cannot outdo your system. In order to run the CLI
in this mode, use the
--intrinsic-latency <test-time>. The test's time
is in seconds, and specifies how many seconds
keydb-cli should check the
latency of the system it's currently running on.
IMPORTANT: this command must be executed on the computer you want to run keydb server on, not on a different host. It does not even connect to a keydb instance and performs the test only locally.
In the above case, my system cannot do better than 739 microseconds of worst case latency, so I can expect certain queries to run in a bit less than 1 millisecond from time to time.
During keydb replication's first synchronization, the master and the replica
exchange the whole data set in form of an RDB file. This feature is exploited
keydb-cli in order to provide a remote backup facility, that allows to
transfer an RDB file from any keydb instance to the local computer running
keydb-cli. To use this mode, call the CLI with the
This is a simple but effective way to make sure you have disaster recovery
RDB backups of your keydb instance. However when using this options in
cron jobs, make sure to check the return value of the command.
If it is non zero, an error occurred like in the following example:
The replica mode of the CLI is an advanced feature useful for
keydb developers and for debugging operations.
It allows to inspect what a master sends to its replica in the replication
stream in order to propagate the writes to its replicas. The option
name is simply
--replica. This is how it works:
The command begins by discarding the RDB file of the first synchronization and then logs each command received as in CSV format.
If you think some of the commands are not replicated correctly in your replicas this is a good way to check what's happening, and also useful information in order to improve the bug report.
keydb is often used as a cache with LRU eviction.
Depending on the number of keys and the amount of memory allocated for the
cache (specified via the
maxmemory directive), the amount of cache hits
and misses will change. Sometimes, simulating the rate of hits is very
useful to correctly provision your cache.
The CLI has a special mode where it performs a simulation of GET and SET operations, using an 80-20% power law distribution in the requests pattern. This means that 20% of keys will be requested 80% of times, which is a common distribution in caching scenarios.
Theoretically, given the distribution of the requests and the keydb memory overhead, it should be possible to compute the hit rate analytically with with a mathematical formula. However, keydb can be configured with different LRU settings (number of samples) and LRU's implementation, which is approximated in keydb, changes a lot between different versions. Similarly the amount of memory per key may change between versions. That is why this tool was built: its main motivation was for testing the quality of keydb' LRU implementation, but now is also useful in for testing how a given version behaves with the settings you had in mind for your deployment.
In order to use this mode, you need to specify the amount of keys
in the test. You also need to configure a
maxmemory setting that
makes sense as a first try.
IMPORTANT NOTE: Configuring the
maxmemory setting in the keydb configuration
is crucial: if there is no cap to the maximum memory usage, the hit will
eventually be 100% since all the keys can be stored in memory. Or if you
specify too many keys and no maximum memory, eventually all the computer
RAM will be used. It is also needed to configure an appropriate
maxmemory policy, most of the times what you want is
In the following example I configured a memory limit of 100MB, and an LRU simulation using 10 million keys.
WARNING: the test uses pipelining and will stress the server, don't use it with production instances.
The program shows stats every second. As you see, in the first seconds the cache starts to be populated. The misses rate later stabilizes into the actual figure we can expect in the long time:
A miss rage of 59% may not be acceptable for our use case. So we know that 100MB of memory is not enough. Let's try with half gigabyte. After a few minutes we'll see the output stabilize to the following figures:
So we know that with 500MB we are going well enough for our number of keys (10 millions) and distribution (80-20 style).