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

<code>$ 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</code>

Running Redis as a Daemon

Modify redis.conf

Change

daemonize no

to

daemonize yes

.

Start Redis

<code>src/redis-server redis.conf</code>

Enable Autostart

Run the installation script with default options.

<code>./utils/install_server.sh</code>

<code>mv /etc/init.d/redis_6379 /etc/init.d/redis</code>

Set Redis Password

<code>vim /etc/redis/6379.conf
requirepass redispass
service redis restart</code>

After reconnecting, a password is required.

Redis Commands

Global Commands

Get Keys

<code>keys pattern</code>

The

keys

command supports wildcards but may affect performance on large datasets.

<code>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"</code>

Delete Keys

<code>del key1 key2 ..</code>

Example:

<code>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"</code>

Check Key Existence

<code>exists key1 key2</code>

Example:

<code>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</code>

Get Total Number of Keys

<code>dbsize</code>

Example:

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

Get Key Type

<code>type key</code>

Example:

<code>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</code>

Sort Elements

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

Example:

<code>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"</code>

Flush Database

<code>flushdb  // clear current DB
flushall // clear all DBs</code>

Example:

<code>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)</code>

Move Key to Another DB

<code>move key db</code>

Example:

<code>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"</code>

String Operations

Set and Get

<code>set key value [EX seconds] [PX milliseconds] [NX|XX]
get key</code>

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

Example:

<code>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</code>

Batch Set/Get

<code>mset key1 value1 key2 value2 ..
mget key1 key2</code>

Example:

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

Increment / Decrement

<code>incr key
decr key</code>

Example:

<code>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</code>

Append

<code>append key value</code>

Example:

<code>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"</code>

String Length

<code>strlen key</code>

Example:

<code>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</code>

Set/Get Sub‑range

<code>setrange key offset value
getrange key start end</code>

Example:

<code>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"</code>

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:

<code>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"</code>

List Operations

Push / Insert

<code>lpush key value1 value2 ...
rpush key value1 value2 ...
linsert key BEFORE|AFTER pivot value</code>

Example:

<code>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"</code>

Pop Elements

<code>lpop key
rpop key</code>

Example:

<code>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"</code>

Index Access

<code>lindex key index</code>

Example:

<code>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"</code>

Range Query

<code>lrange key start stop</code>

Example:

<code>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"</code>

List Length

<code>llen key</code>

Example:

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

Remove Elements

<code>lrem key count value</code>

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

Example:

<code>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"</code>

Set Element by Index

<code>lset key index value</code>

Example:

<code>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"</code>

Blocking Pop

<code>blpop key1 key2 timeout
brpop key1 key2 timeout</code>

Example:

<code>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)</code>

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

<code>hset key field value
hget key field</code>

Example:

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

Batch Set / Get

<code>hmset key field1 value1 field2 value2 ...
hmget key field1 field2 ...</code>

Example:

<code>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"</code>

Delete Field

<code>hdel key field1 field2 ...</code>

Example:

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

Field Count

<code>hlen key</code>

Example:

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

Get All Fields and Values

<code>hgetall key</code>

Example:

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

Get All Field Names

<code>hkeys key</code>

Example:

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

Field Existence

<code>hexists key field</code>

Example:

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

Increment Field

<code>hincrby key field increment</code>

Example:

<code>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"</code>

Get All Values

<code>hvals key</code>

Example:

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

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

<code>sadd key member1 member2 ...</code>

Example:

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

Get All Members

<code>smembers key</code>

Example:

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

Remove Members

<code>srem key member1 member2 ...</code>

Example:

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

Cardinality

<code>scard key</code>

Example:

<code>127.0.0.1:6379> scard set
(integer) 2</code>

Random Member(s)

<code>srandmember key [count]</code>

Example:

<code>127.0.0.1:6379> srandmember set 1
1) "s1"</code>

Membership Test

<code>sismember key member</code>

Example:

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

Pop Members

<code>spop key [count]</code>

Example:

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

Set Union / Intersection / Difference

<code>sunion key1 key2
sinter key1 key2
sdiff key1 key2</code>

Examples:

<code>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"</code>

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

<code>zadd key [NX|XX] [CH] [INCR] score1 member1 score2 member2 ...</code>

Example:

<code>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"</code>

Get Score

<code>zscore key member</code>

Example:

<code>127.0.0.1:6379> zscore score dongdong
"95"</code>

Rank / Reverse Rank

<code>zrank key member   // ascending rank starting at 0
zrevrank key member // descending rank</code>

Example:

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

Cardinality

<code>zcard key</code>

Example:

<code>127.0.0.1:6379> zcard score
(integer) 4</code>

Remove Members

<code>zrem key member1 member2 ...</code>

Example:

<code>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"</code>

Increment Score

<code>zincrby key increment member</code>

Example:

<code>127.0.0.1:6379> zincrby score 5 wanger
"95"</code>

Range by Score

<code>zrangebyscore key min max [WITHSCORES] [LIMIT offset count]
zrevrangebyscore key max min [WITHSCORES] [LIMIT offset count]</code>

Example:

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

Count by Score

<code>zcount key min max</code>

Example:

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

Remove by Score Range

<code>zremrangebyscore key min max</code>

Example:

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

Sorted‑Set Intersection

<code>zinterstore destination numkeys key1 key2 [WEIGHTS w1 w2] [AGGREGATE sum|min|max]</code>

Example:

<code>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"</code>

Sorted‑Set Union

<code>zunionstore destination numkeys key1 key2 [WEIGHTS w1 w2] [AGGREGATE sum|min|max]</code>

Example:

<code>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"</code>

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:

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

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

<code>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</code>

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.