Redis CLI

Overview of redis-cli, the Redis command line interface

In interactive mode, redis-cli has basic line editing capabilities to provide a familiar typing experience.

To launch the program in special modes, you can use several options, including:

Simulate a replica and print the replication stream it receives from the primary.
Check the latency of a Redis server and display statistics.
Request ASCII-art spectrogram of latency samples and frequencies.

This topic covers the different aspects of redis-cli, starting from the simplest and ending with the more advanced features.

Command line usage

To run a Redis command and return a standard output at the terminal, include the command to execute as separate arguments of redis-cli:

$ redis-cli INCR mycounter
(integer) 7

The reply of the command is "7". Since Redis replies are typed (strings, arrays, integers, nil, errors, etc.), you see the type of the reply between parentheses. This additional information may not be ideal when the output of redis-cli must be used as input of another command or redirected into a file.

redis-cli only shows additional information for human readability when it detects the standard output is a tty, or terminal. For all other outputs it will auto-enable the raw output mode, as in the following example:

$ redis-cli INCR mycounter > /tmp/output.txt
$ cat /tmp/output.txt
8

Note that (integer) is omitted from the output because redis-cli detects the output is no longer written to the terminal. You can force raw output even on the terminal with the --raw option:

$ redis-cli --raw INCR mycounter
9

You can force human readable output when writing to a file or in pipe to other commands by using --no-raw.

String quoting and escaping

When redis-cli parses a command, whitespace characters automatically delimit the arguments. In interactive mode, a newline sends the command for parsing and execution. To input string values that contain whitespaces or non-printable characters, you can use quoted and escaped strings.

Quoted string values are enclosed in double (") or single (') quotation marks. Escape sequences are used to put nonprintable characters in character and string literals.

An escape sequence contains a backslash (\) symbol followed by one of the escape sequence characters.

Doubly-quoted strings support the following escape sequences:

\" - double-quote
\n - newline
\r - carriage return
\t - horizontal tab
\b - backspace
\a - alert
\\ - backslash
\xhh - any ASCII character represented by a hexadecimal number (hh)

Single quotes assume the string is literal, and allow only the following escape sequences:

\' - single quote
\\ - backslash

For example, to return Hello World on two lines:

127.0.0.1:6379> SET mykey "Hello\nWorld"
OK
127.0.0.1:6379> GET mykey
Hello
World

When you input strings that contain single or double quotes, as you might in passwords, for example, escape the string, like so:

127.0.0.1:6379> AUTH some_admin_user ">^8T>6Na{u|jp>+v\"55\@_;OU(OR]7mbAYGqsfyu48(j'%hQH7;v*f1H${*gD(Se'"

Host, port, password, and database

By default, redis-cli connects to the server at the address 127.0.0.1 with port 6379. You can change the port using several command line options. To specify a different host name or an IP address, use the -h option. In order to set a different port, use -p.

$ redis-cli -h redis15.localnet.org -p 6390 PING
PONG

If your instance is password protected, the -a <password> option will perform authentication saving the need of explicitly using the AUTH command:

$ redis-cli -a myUnguessablePazzzzzword123 PING
PONG

NOTE: For security reasons, provide the password to redis-cli automatically 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:

$ redis-cli FLUSHALL
OK
$ redis-cli -n 1 INCR a
(integer) 1
$ redis-cli -n 1 INCR a
(integer) 2
$ redis-cli -n 2 INCR a
(integer) 1

Some or all of this information can also be provided by using the -u <uri> option and the URI pattern redis://user:password@host:port/dbnum:

$ redis-cli -u redis://LJenkins:p%[email protected]:16379/0 PING
PONG

NOTE: User, password and dbnum are optional. For authentication without a username, use username default. For TLS, use the scheme rediss.

You can use the -4 or -6 argument to set a preference for IPv4 or IPv6, respectively, for DNS lookups.

SSL/TLS

By default, redis-cli uses a plain TCP connection to connect to Redis. You may enable SSL/TLS using the --tls option, along with --cacert or --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 --cert and --key.

Get input from other programs

There are two ways you can use redis-cli in order to receive input from other commands via the standard input. One is to use the target payload as the last argument from stdin. For example, in order to set the Redis key net_services to the content of the file /etc/services from a local file system, use the -x option:

$ redis-cli -x SET net_services < /etc/services
OK
$ redis-cli GETRANGE net_services 0 50
"#\n# Network services, Internet style\n#\n# Note that "

In the first line of the above session, redis-cli was executed with the -x option and a file was redirected to the CLI's standard input as the value to satisfy the SET net_services command phrase. This is useful for scripting.

A different approach is to feed redis-cli a sequence of commands written in a text file:

$ cat /tmp/commands.txt
SET item:3374 100
INCR item:3374
APPEND item:3374 xxx
GET item:3374
$ cat /tmp/commands.txt | redis-cli
OK
(integer) 101
(integer) 6
"101xxx"

All the commands in commands.txt are executed consecutively by redis-cli as if they were typed by the user in interactive mode. Strings can be quoted inside the file if needed, so that it's possible to have single arguments with spaces, newlines, or other special characters:

$ cat /tmp/commands.txt
SET arg_example "This is a single argument"
STRLEN arg_example
$ cat /tmp/commands.txt | redis-cli
OK
(integer) 25

Continuously run the same command

It is possible to execute a single command a specified number of times with a user-selected pause between 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, such as pushing a new item into a list every 5 seconds.

This feature is controlled by two options: -r <count> and -i <delay>. The -r option states how many times to run a command and -i sets the delay between the different command calls in seconds (with the ability to specify values such as 0.1 to represent 100 milliseconds).

By default the interval (or delay) is set to 0, so commands are just executed ASAP:

$ redis-cli -r 5 INCR counter_value
(integer) 1
(integer) 2
(integer) 3
(integer) 4
(integer) 5

To run the same command indefinitely, use -1 as the count value. To monitor over time the RSS memory size it's possible to use the following command:

$ redis-cli -r -1 -i 1 INFO | grep rss_human
used_memory_rss_human:2.71M
used_memory_rss_human:2.73M
used_memory_rss_human:2.73M
used_memory_rss_human:2.73M
... a new line will be printed each second ...

Mass insertion of data using `redis-cli`

Mass insertion using redis-cli is covered in a separate page as it is a worthwhile topic itself. Please refer to our mass insertion guide.

CSV output

A CSV (Comma Separated Values) output feature exists within redis-cli to export data from Redis to an external program.

$ redis-cli LPUSH mylist a b c d
(integer) 4
$ redis-cli --csv LRANGE mylist 0 -1
"d","c","b","a"

Note that the --csv flag will only work on a single command, not the entirety of a DB as an export.

Run Lua scripts

The redis-cli has extensive support for using the debugging facility of Lua scripting, available with Redis 3.2 onwards. For this feature, refer to the Redis Lua debugger documentation.

Even without using the debugger, redis-cli can be used to run scripts from a file as an argument:

$ cat /tmp/script.lua
return redis.call('SET',KEYS[1],ARGV[1])
$ redis-cli --eval /tmp/script.lua location:hastings:temp , 23
OK

The Redis EVAL command takes the list of keys the script uses, and the other non key arguments, as different arrays. When calling EVAL you provide the number of keys as a number.

When calling redis-cli with the --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 location:hastings:temp , 23 as arguments.

So location:hastings:temp will populate the KEYS array, and 23 the ARGV array.

The --eval option is useful when writing simple scripts. For more complex work, the Lua debugger is recommended. It is possible to mix the two approaches, since the debugger can also execute scripts from an external file.

Interactive mode

We have explored how to use the Redis CLI as a command line program. This is useful for scripts and certain types of testing, however most people will spend the majority of time in redis-cli using its interactive mode.

In interactive mode the user types Redis 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 redis-cli in interactive mode - just execute it without any arguments

$ redis-cli
127.0.0.1:6379> PING
PONG

The string 127.0.0.1:6379> is the prompt. It displays the connected Redis server instance's hostname and port.

The prompt updates as the connected server changes or when operating on a database different from the database number zero:

127.0.0.1:6379> SELECT 2
OK
127.0.0.1:6379[2]> DBSIZE
(integer) 1
127.0.0.1:6379[2]> SELECT 0
OK
127.0.0.1:6379> DBSIZE
(integer) 503

Handle connections and reconnections

Using the 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:

127.0.0.1:6379> CONNECT metal 6379
metal:6379> PING
PONG

As you can see the prompt changes accordingly when connecting to a different server instance. If a connection is attempted to an instance that is unreachable, the redis-cli goes into disconnected mode and attempts to reconnect with each new command:

127.0.0.1:6379> CONNECT 127.0.0.1 9999
Could not connect to Redis at 127.0.0.1:9999: Connection refused
not connected> PING
Could not connect to Redis at 127.0.0.1:9999: Connection refused
not connected> PING
Could not connect to Redis at 127.0.0.1:9999: Connection refused

Generally after a disconnection is detected, redis-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:

127.0.0.1:6379> INFO SERVER
Could not connect to Redis at 127.0.0.1:6379: Connection refused
not connected> PING
PONG
127.0.0.1:6379> 
(now we are connected again)

When a reconnection is performed, redis-cli automatically re-selects the last database number selected. However, all other states about the connection is lost, such as within a MULTI/EXEC transaction:

$ redis-cli
127.0.0.1:6379> MULTI
OK
127.0.0.1:6379> PING
QUEUED

( here the server is manually restarted )

127.0.0.1:6379> EXEC
(error) ERR EXEC without MULTI

This is usually not an issue when using the redis-cli in interactive mode for testing, but this limitation should be known.

Use the -t <timeout> option to specify server timeout in seconds.

Editing, history, completion and hints

Because redis-cli uses the linenoise line editing library, it always has line editing capabilities, without depending on libreadline or other optional libraries.

Command execution history can be accessed in order to avoid retyping commands by pressing the arrow keys (up and down). The history is preserved between restarts of the CLI, in a file named .rediscli_history inside the user home directory, as specified by the HOME environment variable. It is possible to use a different history filename by setting the REDISCLI_HISTFILE environment variable, and disable it by setting it to /dev/null.

The redis-cli client is also able to perform command-name completion by pressing the TAB key, as in the following example:

127.0.0.1:6379> Z<TAB>
127.0.0.1:6379> ZADD<TAB>
127.0.0.1:6379> ZCARD<TAB>

Once Redis command name has been entered at the prompt, the redis-cli will display syntax hints. Like command history, this behavior can be turned on and off via the redis-cli preferences.

Reverse history searches, such as CTRL-R in terminals, is supported.

Preferences

There are two ways to customize redis-cli behavior. The file .redisclirc in the 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 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 .redisclirc file:

:set hints - enables syntax hints
:set nohints - disables syntax hints

Run the same command N times

It is possible to run the same command multiple times in interactive mode by prefixing the command name by a number:

127.0.0.1:6379> 5 INCR mycounter
(integer) 1
(integer) 2
(integer) 3
(integer) 4
(integer) 5

Show online help for Redis commands

redis-cli provides online help for most Redis 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:
- @generic
- @string
- @list
- @set
- @sorted_set
- @hash
- @pubsub
- @transactions
- @connection
- @server
- @scripting
- @hyperloglog
- @cluster
- @geo
- @stream
HELP <commandname> shows specific help for the command given as argument.

For example in order to show help for the PFADD command, use:

127.0.0.1:6379> HELP PFADD

PFADD key element [element ...]
summary: Adds the specified elements to the specified HyperLogLog.
since: 2.8.9

Note that HELP supports TAB completion as well.

Clear the terminal screen

Using the CLEAR command in interactive mode clears the terminal's screen.

Special modes of operation

So far we saw two main modes of redis-cli.

Command line execution of Redis commands.
Interactive "REPL" usage.

The CLI performs other auxiliary tasks related to Redis that are explained in the next sections:

Monitoring tool to show continuous stats about a Redis server.
Scanning a Redis 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 Redis instance.
Checking the latency of a Redis server in different ways.
Checking the scheduler latency of the local computer.
Transferring RDB backups from a remote Redis server locally.
Acting as a Redis replica for showing what a replica receives.
Simulating LRU workloads for showing stats about keys hits.
A client for the Lua debugger.

Continuous stats mode

Continuous stats mode is probably one of the lesser known yet very useful features of redis-cli to monitor Redis 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:

$ redis-cli --stat
------- data ------ --------------------- load -------------------- - child -
keys       mem      clients blocked requests            connections
506        1015.00K 1       0       24 (+0)             7
506        1015.00K 1       0       25 (+1)             7
506        3.40M    51      0       60461 (+60436)      57
506        3.40M    51      0       146425 (+85964)     107
507        3.40M    51      0       233844 (+87419)     157
507        3.40M    51      0       321715 (+87871)     207
508        3.40M    51      0       408642 (+86927)     257
508        3.40M    51      0       497038 (+88396)     257

In this mode a new line is printed every second with useful information and differences of request values between old data points. Memory usage, client connection counts, and various other statistics about the connected Redis database can be easily understood with this auxiliary redis-cli tool.

The -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 second.

Scan for big keys and memory usage

Big keys

In this special mode, redis-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 --bigkeys option, and produces verbose output:

$ redis-cli --bigkeys

# Scanning the entire keyspace to find biggest keys as well as
# average sizes per key type.  You can use -i 0.01 to sleep 0.01 sec
# per SCAN command (not usually needed).

[00.00%] Biggest string found so far 'key-419' with 3 bytes
[05.14%] Biggest list   found so far 'mylist' with 100004 items
[35.77%] Biggest string found so far 'counter:__rand_int__' with 6 bytes
[73.91%] Biggest hash   found so far 'myobject' with 3 fields

-------- summary -------

Sampled 506 keys in the keyspace!
Total key length in bytes is 3452 (avg len 6.82)

Biggest string found 'counter:__rand_int__' has 6 bytes
Biggest   list found 'mylist' has 100004 items
Biggest   hash found 'myobject' has 3 fields

504 strings with 1403 bytes (99.60% of keys, avg size 2.78)
1 lists with 100004 items (00.20% of keys, avg size 100004.00)
0 sets with 0 members (00.00% of keys, avg size 0.00)
1 hashs with 3 fields (00.20% of keys, avg size 3.00)
0 zsets with 0 members (00.00% of keys, avg size 0.00)

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 Redis 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 SCAN command.

For example, -i 0.01 will slow down the program execution considerably, but will also reduce the load on the server to a negligible 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.

The --bigkeys option now works on cluster replicas.

Memory usage

Similar to the --bigkeys option, --memkeys allows you to scan the entire keyspace to find biggest keys as well as the average sizes per key type.

The --memkeys option now works on cluster replicas.

Combine `--bigkeys` and `--memkeys`

You can use the --keystats and --keystats-samples options to combine --memkeys and --bigkeys with additional distribution data.

Get a list of keys

It is also possible to scan the key space, again in a way that does not block the Redis server (which does happen when you use a command like KEYS *), and print all the key names, or filter them for specific patterns. This mode, like the --bigkeys option, uses the SCAN command, 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 --scan.

$ redis-cli --scan | head -10
key-419
key-71
key-236
key-50
key-38
key-458
key-453
key-499
key-446
key-371

Note that head -10 is used in order to print only the first ten lines of the output.

Scanning is able to use the underlying pattern matching capability of the SCAN command with the --pattern option.

$ redis-cli --scan --pattern '*-11*'
key-114
key-117
key-118
key-113
key-115
key-112
key-119
key-11
key-111
key-110
key-116

Piping the output through the wc command can be used to count specific kind of objects, by key name:

$ redis-cli --scan --pattern 'user:*' | wc -l
3829433

You can use -i 0.01 to add a delay between calls to the SCAN command. This will make the command slower but will significantly reduce load on the server.

Pub/sub mode

The CLI is able to publish messages in Redis Pub/Sub channels using the PUBLISH command. Subscribing to channels in order to receive messages is different - the terminal is blocked and waits for messages, so this is implemented as a special mode in redis-cli. Unlike other special modes this mode is not enabled by using a special option, but simply by using the SUBSCRIBE or PSUBSCRIBE command, which are available in interactive or command mode:

$ redis-cli PSUBSCRIBE '*'
Reading messages... (press Ctrl-C to quit)
1) "PSUBSCRIBE"
2) "*"
3) (integer) 1

The reading messages message shows that we entered Pub/Sub mode. When another client publishes some message in some channel, such as with the command redis-cli PUBLISH mychannel mymessage, the CLI in Pub/Sub mode will show something such as:

1) "pmessage"
2) "*"
3) "mychannel"
4) "mymessage"

This is very useful for debugging Pub/Sub issues. To exit the Pub/Sub mode just process CTRL-C.

Monitor commands executed in Redis

Similarly to the Pub/Sub mode, the monitoring mode is entered automatically once you use the MONITOR command. All commands received by the active Redis instance will be printed to the standard output:

$ redis-cli MONITOR
OK
1460100081.165665 [0 127.0.0.1:51706] "set" "shipment:8000736522714:status" "sorting"
1460100083.053365 [0 127.0.0.1:51707] "get" "shipment:8000736522714:status"

Note that it is possible to pipe the output, so you can monitor for specific patterns using tools such as grep.

Monitor the latency of Redis instances

Redis 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 Redis instance itself.

The redis-cli has multiple facilities for studying the latency of a Redis 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 Redis instance and the time to receive a reply is measured. This happens 100 times per second, and stats are updated in a real time in the console:

$ redis-cli --latency
min: 0, max: 1, avg: 0.19 (427 samples)

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 redis-cli 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 most developers are interested in events of a few milliseconds 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:

$ redis-cli --latency-history
min: 0, max: 1, avg: 0.14 (1314 samples) -- 15.01 seconds range
min: 0, max: 1, avg: 0.18 (1299 samples) -- 15.00 seconds range
min: 0, max: 1, avg: 0.20 (113 samples)^C

Sampling sessions' length can be changed with the -i <interval> option.

The most advanced latency study tool, but also the most complex 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 --latency-dist option:

$ redis-cli --latency-dist
(output not displayed, requires a color terminal, try it!)

There is another pretty unusual latency tool implemented inside redis-cli. It does not check the latency of a Redis instance, but the latency of the computer running redis-cli. This latency is intrinsic to the kernel scheduler, the hypervisor in case of virtualized instances, and so forth.

Redis calls it intrinsic latency because it's mostly opaque to the programmer. If the Redis instance has high 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 redis-cli in this special mode directly in the system you are running Redis servers on.

By measuring the intrinsic latency, you know that this is the baseline, and Redis cannot outdo your system. In order to run the CLI in this mode, use the --intrinsic-latency <test-time>. Note that the test time is in seconds and dictates how long the test should run.

$ ./redis-cli --intrinsic-latency 5
Max latency so far: 1 microseconds.
Max latency so far: 7 microseconds.
Max latency so far: 9 microseconds.
Max latency so far: 11 microseconds.
Max latency so far: 13 microseconds.
Max latency so far: 15 microseconds.
Max latency so far: 34 microseconds.
Max latency so far: 82 microseconds.
Max latency so far: 586 microseconds.
Max latency so far: 739 microseconds.

65433042 total runs (avg latency: 0.0764 microseconds / 764.14 nanoseconds per run).
Worst run took 9671x longer than the average latency.

IMPORTANT: this command must be executed on the computer that runs the Redis server instance, not on a different host. It does not connect to a Redis instance and performs the test locally.

In the above case, the system cannot do better than 739 microseconds of worst case latency, so one can expect certain queries to occasionally run less than 1 millisecond.

Remote backups of RDB files

During a Redis replication's first synchronization, the primary and the replica exchange the whole data set in the form of an RDB file. This feature is exploited by redis-cli in order to provide a remote backup facility that allows a transfer of an RDB file from any Redis instance to the local computer running redis-cli. To use this mode, call the CLI with the --rdb <dest-filename> option:

$ redis-cli --rdb /tmp/dump.rdb
SYNC sent to master, writing 13256 bytes to '/tmp/dump.rdb'
Transfer finished with success.

This is a simple but effective way to ensure disaster recovery RDB backups exist of your Redis instance. When using this options in scripts or cron jobs, make sure to check the return value of the command. If it is non zero, an error occurred as in the following example:

$ redis-cli --rdb /tmp/dump.rdb
SYNC with master failed: -ERR Can't SYNC while not connected with my master
$ echo $?
1

Replica mode

The replica mode of the CLI is an advanced feature useful for Redis developers and for debugging operations. It allows for the inspection of the content a primary sends to its replicas in the replication stream in order to propagate the writes to its replicas. The option name is simply --replica. The following is a working example:

$ redis-cli --replica
SYNC with master, discarding 13256 bytes of bulk transfer...
SYNC done. Logging commands from master.
"PING"
"SELECT","0"
"SET","last_name","Enigk"
"PING"
"INCR","mycounter"

The command begins by discarding the RDB file of the first synchronization and then logs each command received 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.

Perform an LRU simulation

Redis 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 redis-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 Redis memory overhead, it should be possible to compute the hit rate analytically with a mathematical formula. However, Redis can be configured with different LRU settings (number of samples) and LRU's implementation, which is approximated in Redis, 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 Redis' LRU implementation, but now is also useful for testing how a given version behaves with the settings originally intended for deployment.

To use this mode, specify the amount of keys in the test and configure a sensible maxmemory setting as a first attempt.

IMPORTANT NOTE: Configuring the maxmemory setting in the Redis 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. If too many keys are specified with maximum memory, eventually all of the computer RAM will be used. It is also needed to configure an appropriate maxmemory policy; most of the time allkeys-lru is selected.

In the following example there is a 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.

$ ./redis-cli --lru-test 10000000
156000 Gets/sec | Hits: 4552 (2.92%) | Misses: 151448 (97.08%)
153750 Gets/sec | Hits: 12906 (8.39%) | Misses: 140844 (91.61%)
159250 Gets/sec | Hits: 21811 (13.70%) | Misses: 137439 (86.30%)
151000 Gets/sec | Hits: 27615 (18.29%) | Misses: 123385 (81.71%)
145000 Gets/sec | Hits: 32791 (22.61%) | Misses: 112209 (77.39%)
157750 Gets/sec | Hits: 42178 (26.74%) | Misses: 115572 (73.26%)
154500 Gets/sec | Hits: 47418 (30.69%) | Misses: 107082 (69.31%)
151250 Gets/sec | Hits: 51636 (34.14%) | Misses: 99614 (65.86%)

The program shows stats every second. In the first seconds the cache starts to be populated. The misses rate later stabilizes into the actual figure that can be expected:

120750 Gets/sec | Hits: 48774 (40.39%) | Misses: 71976 (59.61%)
122500 Gets/sec | Hits: 49052 (40.04%) | Misses: 73448 (59.96%)
127000 Gets/sec | Hits: 50870 (40.06%) | Misses: 76130 (59.94%)
124250 Gets/sec | Hits: 50147 (40.36%) | Misses: 74103 (59.64%)

A miss rate of 59% may not be acceptable for certain use cases therefor 100MB of memory is not enough. Observe an example using a half gigabyte of memory. After several minutes the output stabilizes to the following figures:

140000 Gets/sec | Hits: 135376 (96.70%) | Misses: 4624 (3.30%)
141250 Gets/sec | Hits: 136523 (96.65%) | Misses: 4727 (3.35%)
140250 Gets/sec | Hits: 135457 (96.58%) | Misses: 4793 (3.42%)
140500 Gets/sec | Hits: 135947 (96.76%) | Misses: 4553 (3.24%)

With 500MB there is sufficient space for the key quantity (10 million) and distribution (80-20 style).