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cheatsheet
2022-06-03
2022-06-03
Redis Cheat Sheet
When you encounter a Redis instance and you quickly want to learn about the setup you just need a few simple commands to peak into the setup. Of course it doesn’t hurt to look at the official full command documentation, but below is a listing just for sysadmins.
Accessing Redis
CLI
First thing to know is that you can use “telnet” (usually on Redis default port 6379)
telnet localhost 6379
or the Redis CLI client
redis-cli
to connect to Redis. The advantage of redis-cli is that you have a help interface and command line history.
CLI Queries
Here is a short list of some basic data extraction commands:
Type Syntax and Explanation
Tracing monitor Watch current live commands. Use with care when on production. Cancel with Ctrl-C.
Slow Queries slowlog get 25 Print top 25 slow queries
slowlog len
slowlog reset
Search / List All Keys keys <pattern Use with care when on production!
keys myprefix*
keys pattern
keys *mysuffix
keys [a-c]* Use grep like expressions
Generic Key Handling del
dump
exists
expire
Working with scalar types get
set
setnx
Batch commands:
mget
mset
Working with counters incr
decr
Redis Lists lrange
lrange mylist 0 -1 Output all elements
lindex mylist 5 Get 5th element
llen mylist Get list length
lpush mylist “value” Push “value” to list
lpush mylist 5 Push number 5 to list
rpush mylist “value” Push “value” to beginning (unshift)
lpushx mylist 6 Only push if mylist exists
rpushx mylist 7
lpop mylist Remove+return value from list
rpop mylist Remove+return value from start (shift)
lrem mylist 1 “value” Remove ‘value’ count times
lset mylist 2 6 Set 3rd element to value 6
ltrim
Working with Redis Hashes hexists myhash field1 Check if hash key exists
hget myhash field1 Get key value
hdel myhash field2 Delete key
hset myhash field1 “value” Set key with “value”
hsetnx myhash field1 “value”
hgetall myhash Get all hash content
hkeys myhash List all keys
hlen myhash List number of keys
Batch commands:
hmget
hmset
Counter commands
hincrby myhash field1 1
hincrby myhash field1 5
hincrby myhash field1 -1
hincrbrfloat myhash field2 1.123445
CLI Scripting
For scripting just pass commands to “redis-cli”. For example:
$ redis-cli INFO | grep connected
connected_clients:2
connected_slaves:0
$
Server Statistics
The statistics command is “INFO” and will give you an output as following.
$ redis-cli INFO
redis_version:2.2.12
redis_git_sha1:00000000
redis_git_dirty:0
arch_bits:64
multiplexing_api:epoll
process_id:8353
uptime_in_seconds:2592232
uptime_in_days:30
lru_clock:809325
used_cpu_sys:199.20
used_cpu_user:309.26
used_cpu_sys_children:12.04
used_cpu_user_children:1.47
connected_clients:2 # <—- connection count
connected_slaves:0
client_longest_output_list:0
client_biggest_input_buf:0
blocked_clients:0
used_memory:6596112
used_memory_human:6.29M # <—- memory usage
used_memory_rss:17571840
mem_fragmentation_ratio:2.66
use_tcmalloc:0
loading:0
aof_enabled:0
changes_since_last_save:0
bgsave_in_progress:0
last_save_time:1371241671
bgrewriteaof_in_progress:0
total_connections_received:118
total_commands_processed:1091
expired_keys:441
evicted_keys:0
keyspace_hits:6
keyspace_misses:1070
hash_max_zipmap_entries:512
hash_max_zipmap_value:64
pubsub_channels:0
pubsub_patterns:0
vm_enabled:0
role:master # <—- master/slave in replication setup
db0:keys=91,expires=88
Changing Runtime Configuration
The command
CONFIG GET *
gives you a list of all active configuration variables you can change. The output might look like this:
redis 127.0.0.1:6379> CONFIG GET *
“dir”
“/var/lib/redis”
“dbfilename”
“dump.rdb”
“requirepass”
(nil)
“masterauth”
(nil)
“maxmemory”
“0”
“maxmemory-policy”
“volatile-lru”
“maxmemory-samples”
“3”
“timeout”
“300”
“appendonly”
“no”
“no-appendfsync-on-rewrite”
“no”
“appendfsync”
“everysec” # <—- how often fsync() is called
“save”
“900 1 300 10 60 10000” # <—- how often Redis dumps in background
“slave-serve-stale-data”
“yes”
“hash-max-zipmap-entries”
“512”
“hash-max-zipmap-value”
“64”
“list-max-ziplist-entries”
“512”
“list-max-ziplist-value”
“64”
“set-max-intset-entries”
“512”
“slowlog-log-slower-than”
“10000”
“slowlog-max-len”
“64”
Note that keys and values are alternating and you can change each key by issuing a “CONFIG SET” command like:
CONFIG SET timeout 900
Such a change will be effective instantly. When changing values consider also updating the redis configuration file.
Databases
Multiple Databases
Redis has a concept of separated namespaces called “databases”. You can select the database number you want to use with “SELECT”. By default the database with index 0 is used. So issuing
redis 127.0.0.1:6379> SELECT 1
OK
redis 127.0.0.1:6379[1]>
switches to the second database. Note how the prompt changed and now has a “[1]” to indicate the database selection. To find out how many databases there are you might want to run redis-cli from the shell:
$ redis-cli INFO | grep ^db
db0:keys=91,expires=88
db1:keys=1,expires=0
Dropping Databases
To drop the currently selected database run
FLUSHDB
to drop all databases at once run
FLUSHALL
Replication
Checking for Replication
To see if the instance is a replication slave or master issue
redis 127.0.0.1:6379> INFO
[…]
role:master
and watch for the “role” line which shows either “master” or “slave”. Starting with version 2.8 the “INFO” command also gives you per slave replication status looking like this
slave0:ip=127.0.0.1,port=6380,state=online,offset=281,lag=0
Setting up Replication
If you quickly need to set up replication just issue
SLAVEOF
on a machine that you want to become slave of the given IP. It will immediately get values from the master. Note that this instance will still be writable. If you want it to be read-only change the redis config file (only available in most recent version, e.g. not on Debian). To revert the slave setting run
SLAVEOF NO ONE
Performance Testing
Benchmark
Install the Redis tools and run the provided benchmarking tool
redis-benchmark -h
If you are migrating from/to memcached protocol check out how to run the same benchmark for any key value store with memcached protocol.
Debugging Latency
First measure system latency on your Redis server with
redis-cli –intrinsic-latency 100
and then sample from your Redis clients with
redis-cli –latency -h
If you have problems with high latency check if transparent huge pages are disabled. Disable it with
echo never > /sys/kernel/mm/transparent_hugepage/enabled
Dump Database Backup
As Redis allows RDB database dumps in background, you can issue a dump at any time. Just run:
BGSAVE
When running this command Redis will fork and the new process will dump into the “dbfilename” configured in the Redis configuration without the original process being blocked. Of course the fork itself might cause an interruption. Use “LASTSAVE” to check when the dump file was last updated. For a simple backup solution just backup the dump file. If you need a synchronous save run “SAVE” instead of “BGSAVE”.
Listing Connections
Starting with version 2.4 you can list connections with
CLIENT LIST
and you can terminate connections with
CLIENT KILL
Monitoring Traffic
The propably most useful command compared to memcached where you need to trace network traffic is the “MONITOR” command which will dump incoming commands in real time.
redis 127.0.0.1:6379> MONITOR
OK
1371241093.375324 “monitor”
1371241109.735725 “keys” “*”
1371241152.344504 “set” “testkey” “1”
1371241165.169184 “get” “testkey”
additionally use “SLOWLOG” to track the slowest queries in an interval. For example
SLOWLOG RESET
wait for some time
SLOWLOG GET 25
and get the 25 slowest command during this time.
Sharding with proxies
There are two major proxy solutions
Twemproxy (aka nutcracker, by Twitter)
Codis