Master Redis: Installation, Commands, and Persistence Explained

Redis Overview

Redis is an open‑source, ANSI‑C written, BSD‑licensed, network‑enabled, in‑memory (with optional persistence) key‑value database that supports strings, hashes, lists, sets and sorted sets.

Installing Redis

$ wget http://download.redis.io/releases/redis-5.0.5.tar.gz
$ tar xzf redis-5.0.5.tar.gz
$ cd redis-5.0.5
$ make

Running Redis as a Daemon

Modify redis.conf

Change daemonize no to daemonize yes.

Start Redis

src/redis-server redis.conf

Enable Autostart

Run the installation script with default options.

./utils/install_server.sh

mv /etc/init.d/redis_6379 /etc/init.d/redis

Set Redis Password

vim /etc/redis/6379.conf
requirepass redispass
service redis restart

After reconnecting, a password is required.

Redis Commands

Global Commands

Get Keys

keys pattern

The keys command supports wildcards but may affect performance on large datasets.

127.0.0.1:6379> set we "hello"
OK
127.0.0.1:6379> keys *
1) "we"
127.0.0.1:6379> set name wanger
OK
127.0.0.1:6379> keys name
1) "name"
127.0.0.1:6379> keys *
1) "name"
2) "we"

Delete Keys

del key1 key2 ..

Example:

127.0.0.1:6379> keys *
1) "qwe"
2) "asd"
3) "we"
127.0.0.1:6379> del asd qwe
(integer) 2
127.0.0.1:6379> keys *
1) "we"

Check Key Existence

exists key1 key2

Example:

127.0.0.1:6379> exists we
(integer) 1
127.0.0.1:6379> exists name
(integer) 0
127.0.0.1:6379> set qwe 2
OK
127.0.0.1:6379> exists we qwe
(integer) 2
127.0.0.1:6379> exists we name
(integer) 1

Get Total Number of Keys

dbsize

Example:

127.0.0.1:6379> dbsize
(integer) 2
127.0.0.1:6379> keys *
1) "qwe"
2) "we"

Get Key Type

type key

Example:

127.0.0.1:6379> type we
string
127.0.0.1:6379> lpush list1 1 2 3
(integer) 3
127.0.0.1:6379> type list1
list

Sort Elements

sort key [BY pattern] [LIMIT offset count] [GET pattern ...] [ASC|DESC] [ALPHA] [STORE destination]

Example:

127.0.0.1:6379> lrange list 0 -1
1) "5"
2) "7"
3) "2"
4) "4"
5) "3"
6) "1"
sort list desc limit 0 5
1) "7"
2) "5"
3) "4"
4) "4"
5) "3"
127.0.0.1:6379> lpush list2 asd qwe zxc
(integer) 3
sort list2 desc limit 0 5 alpha
1) "zxc"
2) "qwe"
3) "asd"

Flush Database

flushdb  // clear current DB
flushall // clear all DBs

Example:

127.0.0.1:6379> set a 1
OK
127.0.0.1:6379> get a
"1"
127.0.0.1:6379> flushdb
OK
127.0.0.1:6379> get a
(nil)

Move Key to Another DB

move key db

Example:

127.0.0.1:6379> set a 1
OK
127.0.0.1:6379> move a 2
(integer) 1
127.0.0.1:6379> select 2
OK
127.0.0.1:6379> get a
"1"

String Operations

Set and Get

set key value [EX seconds] [PX milliseconds] [NX|XX]
get key

NX : set only if key does not exist. XX : set only if key exists.

Example:

127.0.0.1:6379> set name wanger
OK
127.0.0.1:6379> get name
"wanger"
127.0.0.1:6379> setnx name wanger
(integer) 0
127.0.0.1:6379> set name wang xx
OK

Batch Set/Get

mset key1 value1 key2 value2 ..
mget key1 key2

Example:

127.0.0.1:6379> mset key1 1 key2 2
OK
127.0.0.1:6379> mget key1 key2
1) "1"
2) "2"

Increment / Decrement

incr key
decr key

Example:

127.0.0.1:6379> incr key1
(integer) 2
127.0.0.1:6379> incr key2
(integer) 3
127.0.0.1:6379> get key1
"2"
127.0.0.1:6379> get key2
"3"
127.0.0.1:6379> incr we
(error) ERR value is not an integer or out of range
127.0.0.1:6379> decr key1
(integer) 1
127.0.0.1:6379> decr key2
(integer) 2

Append

append key value

Example:

127.0.0.1:6379> append key hello
(integer) 5
127.0.0.1:6379> append key world
(integer) 10
127.0.0.1:6379> get key
"helloworld"

String Length

strlen key

Example:

127.0.0.1:6379> get key
"helloworld"
127.0.0.1:6379> strlen key
(integer) 10
127.0.0.1:6379> set name "王二"
OK
127.0.0.1:6379> strlen name
(integer) 6

Set/Get Sub‑range

setrange key offset value
getrange key start end

Example:

127.0.0.1:6379> SET key1 "Hello World"
OK
127.0.0.1:6379> setrange key1 6 "Redis"
(integer) 11
127.0.0.1:6379> get key1
"Hello Redis"
127.0.0.1:6379> getrange key1 6 12
"Redis"

String Object Encoding

Redis stores strings using three internal encodings:

int : 8‑byte integer.

embstr : strings up to 39 bytes.

raw : strings longer than 39 bytes.

Example:

127.0.0.1:6379> set num 123456
OK
127.0.0.1:6379> object encoding num
"int"
127.0.0.1:6379> set short qweasd
OK
127.0.0.1:6379> object encoding short
"embstr"
127.0.0.1:6379> set raw "when you love me I have lost of plot wow wow"
OK
127.0.0.1:6379> object encoding raw
"raw"

List Operations

Push / Insert

lpush key value1 value2 ...
rpush key value1 value2 ...
linsert key BEFORE|AFTER pivot value

Example:

127.0.0.1:6379> lpush names 1 2 3 4
(integer) 4
127.0.0.1:6379> lrange names 0 4
1) "4"
2) "3"
3) "2"
4) "1"
127.0.0.1:6379> rpush nums 1 2 3 4
(integer) 4
127.0.0.1:6379> lrange nums 0 4
1) "1"
2) "2"
3) "3"
4) "4"
127.0.0.1:6379> linsert nums BEFORE 2 5
(integer) 5
127.0.0.1:6379> lrange nums 0 5
1) "1"
2) "5"
3) "2"
4) "3"
5) "4"

Pop Elements

lpop key
rpop key

Example:

127.0.0.1:6379> lrange nums 0 5
1) "1"
2) "5"
3) "2"
4) "3"
5) "4"
127.0.0.1:6379> lpop nums
"1"
127.0.0.1:6379> rpop nums
"4"
127.0.0.1:6379> lrange nums 0 5
1) "5"
2) "2"
3) "3"

Index Access

lindex key index

Example:

127.0.0.1:6379> lrange nums 0 5
1) "5"
2) "2"
3) "3"
127.0.0.1:6379> lindex nums 2
"3"
127.0.0.1:6379> lindex nums -1
"3"

Range Query

lrange key start stop

Example:

127.0.0.1:6379> lrange nums 0 1
1) "5"
2) "2"
127.0.0.1:6379> lrange nums 0 2
1) "5"
2) "2"
3) "3"

List Length

llen key

Example:

127.0.0.1:6379> lrange nums 0 3
1) "5"
2) "2"
3) "3"
127.0.0.1:6379> llen nums
(integer) 3

Remove Elements

lrem key count value

count > 0: remove from head; count < 0: remove from tail; count = 0: remove all.

Example:

127.0.0.1:6379> lrange mylist 0 10
1) "1"
2) "2"
3) "3"
4) "4"
5) "5"
6) "2"
7) "3"
8) "4"
9) "5"
10) "5"
127.0.0.1:6379> lrem mylist 1 5
(integer) 1
127.0.0.1:6379> lrange mylist 0 10
1) "1"
2) "2"
3) "3"
4) "4"
5) "2"
6) "3"
7) "4"
8) "5"
9) "5"
127.0.0.1:6379> lrem mylist -2 5
(integer) 2
127.0.0.1:6379> lrange mylist 0 10
1) "1"
2) "2"
3) "3"
4) "4"
5) "2"
6) "3"
7) "4"
127.0.0.1:6379> lrem mylist 0 2
(integer) 2
127.0.0.1:6379> lrange mylist 0 11
1) "1"
2) "3"
3) "4"
4) "3"
5) "4"

Set Element by Index

lset key index value

Example:

127.0.0.1:6379> lrange mylist 0 6
1) "1"
2) "3"
3) "4"
4) "3"
5) "4"
127.0.0.1:6379> lset mylist 1 5
OK
127.0.0.1:6379> lrange mylist 0 6
1) "1"
2) "5"
3) "4"
4) "3"
5) "4"

Blocking Pop

blpop key1 key2 timeout
brpop key1 key2 timeout

Example:

127.0.0.1:6379> blpop list1 list2 0
1) "list1"
2) "8"
127.0.0.1:6379> brpop list1 list2 0
1) "list1"
2) "7"
127.0.0.1:6379> brpop list1 list2 0
1) "list2"
2) "2"
... (continues until another client pushes data)

List Internal Encoding

ziplist : used when all elements are < 64 bytes and the list has < 512 items.

linkedlist : fallback when ziplist conditions are not met.

quicklist : a linked list of ziplist nodes, the default implementation in modern Redis.

Reference: 张铁蕾 http://zhangtielei.com/posts/blog-redis-quicklist.html

Hash Operations

Set / Get Field

hset key field value
hget key field

Example:

127.0.0.1:6379> hset ha name wanger
(integer) 1
127.0.0.1:6379> hget ha name
"wanger"

Batch Set / Get

hmset key field1 value1 field2 value2 ...
hmget key field1 field2 ...

Example:

127.0.0.1:6379> hmset he name wanger sex nan
OK
127.0.0.1:6379> hmget he name sex
1) "wanger"
2) "nan"

Delete Field

hdel key field1 field2 ...

Example:

127.0.0.1:6379> hdel he name
(integer) 1
127.0.0.1:6379> hget he name
(nil)

Field Count

hlen key

Example:

127.0.0.1:6379> hmset he name wanger sex nan age 18
OK
127.0.0.1:6379> hlen he
(integer) 3

Get All Fields and Values

hgetall key

Example:

127.0.0.1:6379> hgetall he
1) "sex"
2) "nan"
3) "name"
4) "wanger"
5) "age"
6) "18"

Get All Field Names

hkeys key

Example:

127.0.0.1:6379> hkeys he
1) "sex"
2) "name"
3) "age"

Field Existence

hexists key field

Example:

127.0.0.1:6379> hexists he name
(integer) 1
127.0.0.1:6379> hexists he sex
(integer) 1

Increment Field

hincrby key field increment

Example:

127.0.0.1:6379> hincrby asd asdf 2
(integer) 3
127.0.0.1:6379> hget asd asdf
"3"
127.0.0.1:6379> hincrby asd asdf 2
(integer) 5
127.0.0.1:6379> hget asd asdf
"5"

Get All Values

hvals key

Example:

127.0.0.1:6379> hvals he
1) "nan"
2) "wanger"
3) "18"

Hash Internal Encoding

ziplist : used when the hash has fewer than 512 entries and each value is under 64 bytes.

hashtable : used otherwise, offering O(1) access.

Set Operations

Add Members

sadd key member1 member2 ...

Example:

127.0.0.1:6379> sadd set s1 s2
(integer) 0

Get All Members

smembers key

Example:

127.0.0.1:6379> smembers set
1) "s2"
2) "s1"
3) "s3"

Remove Members

srem key member1 member2 ...

Example:

127.0.0.1:6379> srem set s2
(integer) 1
127.0.0.1:6379> smembers set
1) "s1"
2) "s3"

Cardinality

scard key

Example:

127.0.0.1:6379> scard set
(integer) 2

Random Member(s)

srandmember key [count]

Example:

127.0.0.1:6379> srandmember set 1
1) "s1"

Membership Test

sismember key member

Example:

127.0.0.1:6379> sismember set s2
(integer) 0
127.0.0.1:6379> sismember set s3
(integer) 1

Pop Members

spop key [count]

Example:

127.0.0.1:6379> spop set
"s4"
127.0.0.1:6379> spop set 3
1) "s5"
2) "s1"
3) "s3"

Set Union / Intersection / Difference

sunion key1 key2
sinter key1 key2
sdiff key1 key2

Examples:

127.0.0.1:6379> sunion set1 set2
1) "1"
2) "2"
3) "3"
4) "4"
5) "5"
127.0.0.1:6379> sinter set1 set2
1) "2"
2) "3"
127.0.0.1:6379> sdiff set1 set2
1) "1"
127.0.0.1:6379> sdiff set2 set1
1) "4"
2) "5"

Set Internal Encoding

intset : used when all members are integers and the set has fewer than 512 entries.

hashtable : fallback for larger or non‑integer sets.

Sorted Set Operations

Add Members

zadd key [NX|XX] [CH] [INCR] score1 member1 score2 member2 ...

Example:

127.0.0.1:6379> zadd score xx 80 wanger 80 huazai 95 dongdong +inf a
(integer) 0
127.0.0.1:6379> zrange score 0 -1
1) "huazai"
2) "wanger"
3) "dongdong"
4) "a"

Get Score

zscore key member

Example:

127.0.0.1:6379> zscore score dongdong
"95"

Rank / Reverse Rank

zrank key member   // ascending rank starting at 0
zrevrank key member // descending rank

Example:

127.0.0.1:6379> zrank score huazai
(integer) 2
127.0.0.1:6379> zrevrank score huazai
(integer) 1

Cardinality

zcard key

Example:

127.0.0.1:6379> zcard score
(integer) 4

Remove Members

zrem key member1 member2 ...

Example:

127.0.0.1:6379> zrem score dongdong
(integer) 1
127.0.0.1:6379> zrange score 0 -1
1) "wanger"
2) "huazai"
3) "a"

Increment Score

zincrby key increment member

Example:

127.0.0.1:6379> zincrby score 5 wanger
"95"

Range by Score

zrangebyscore key min max [WITHSCORES] [LIMIT offset count]
zrevrangebyscore key max min [WITHSCORES] [LIMIT offset count]

Example:

127.0.0.1:6379> zrangebyscore score 80 90 WITHSCORES
1) "dongdong"
2) "85"
3) "wanger"
4) "90"

Count by Score

zcount key min max

Example:

127.0.0.1:6379> zcount score 85 95
(integer) 3

Remove by Score Range

zremrangebyscore key min max

Example:

127.0.0.1:6379> zremrangebyscore score 85 90
(integer) 2

Sorted‑Set Intersection

zinterstore destination numkeys key1 key2 [WEIGHTS w1 w2] [AGGREGATE sum|min|max]

Example:

127.0.0.1:6379> zadd user 10 wanger 20 huazai 30 dongdong
(integer) 3
127.0.0.1:6379> zadd user1 15 wanger 35 huazai
(integer) 2
127.0.0.1:6379> zinterstore userset 2 user user1
(integer) 2
127.0.0.1:6379> zrange userset 0 -1 WITHSCORES
1) "wanger"
2) "25"
3) "huazai"
4) "55"

Sorted‑Set Union

zunionstore destination numkeys key1 key2 [WEIGHTS w1 w2] [AGGREGATE sum|min|max]

Example:

127.0.0.1:6379> zunionstore user3set 2 user user1 WEIGHTS 1 0.5 AGGREGATE MAX
(integer) 3
127.0.0.1:6379> zrange user3set 0 -1 WITHSCORES
1) "wanger"
2) "10"
3) "huazai"
4) "20"
5) "dongdong"
6) "30"

Sorted‑Set Internal Encoding

ziplist : used when the set has fewer than 128 elements and each element is under 64 bytes.

skiplist : used otherwise, providing O(log N) range queries.

Redis Persistence

RDB (Snapshotting)

RDB creates a point‑in‑time snapshot of the dataset and writes it to a binary file. The snapshot can be loaded on restart for fast recovery and is suitable for backups.

RDB Process

Redis forks a child process.

The child writes the dataset to a temporary RDB file.

When finished, the temporary file replaces the old RDB file.

Automatic Trigger

Configured in redis.conf (e.g., save 900 1, save 300 10, save 60 10000).

Additional options:

rdbcompression yes
rdbchecksum yes
dbfilename dump.rdb
dir /var/lib/redis/6379

Manual Trigger

Use SAVE (blocks the server) or BGSAVE (forks a child and continues serving clients).

AOF (Append‑Only File)

AOF logs every write operation using the Redis protocol. On restart, the log is replayed to rebuild the dataset. A background rewrite compresses the log when it grows large.

AOF Write Strategies

appendfsync always

: sync on every write (slow, no data loss). appendfsync everysec: sync every second (default, may lose up to 1 s). appendfsync no: let the OS handle syncing (fast, riskier).

AOF Rewrite

When the AOF becomes large, Redis forks a child that rewrites the log by reading the in‑memory dataset and emitting the minimal set of commands. New writes are buffered and appended to the old AOF; after the rewrite finishes, the temporary file replaces the old AOF.

AOF Configuration

no-appendfsync-on-rewrite no
auto-aof-rewrite-percentage 100
auto-aof-rewrite-min-size 64mb
aof-rewrite-incremental-fsync yes
aof-use-rdb-preamble yes

When both RDB and AOF files exist, AOF takes precedence for recovery.

Reference: Zhang Tielei – https://zhangtielei.com/posts/blog-redis-quicklist.html

Feel free to discuss and share insights.