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Redis Learning Note

redis.io

Documentation
An introduction to Redis data types and abstractions
Redis interactive tutorial

Installation

You can download redis from redis.io or from http://download.redis.io/redis-stable.tar.gz to download stable version.

Compile Redis follow this steps:

wget http://download.redis.io/redis-stable.tar.gz
tar xvzf redis-stable.tar.gz
cd redis-stable
make

After the compilation the src directory inside the Redis distribution is populated with the different executables that are part of Redis:

  • redis-server is the Redis Server itself.
  • redis-sentinel is the Redis Sentinel executable (monitoring and failover).
  • redis-cli is the command line interface utility to talk with Redis.
  • redis-benchmark is used to check Redis performances.
  • redis-check-aof and redis-check-dump are useful in the rare event of corrupted data files

Recommend steps:

# sudo cp src/redis-server /usr/local/bin/
# sudo cp src/redis-cli /usr/local/bin/

Starting

Just run src/redis-server to start redis and src/redis-cli to start command line utility, if you did the recommend steps above, just run redis-server and redis-cli.

Start Redis with a configuration file:

$ redis-server /etc/redis.conf

The first thing to do in order to check if Redis is working properly is sending a PING command using redis-cli:

$ redis-cli ping
PONG

Redis-cli will send commands to the Redis instance running on localhost at port 6379.

Redis data types and operations

Redis keys

Redis keys are binary safe, this means that you can use any binary sequence as a key.

  • Very long keys are not a good idea. (Memory and efficiency)
  • Very short keys are often not a good idea. (Readable)
  • Try to stick with a schema.
  • The maximum allowed key size is 512 MB.

Strings

Using the SET and the GET commands are the way we set and retrieve a string value. Note that SET will replace any existing value already stored into the key.

The INCR command parses the string value as an integer, increments it by one. There are other similar commands like INCRBY, DECR and DECRBY.
INCR is atomic!

Other String operations:

  • GETSET: sets a key to a new value, returning the old value as the result.
  • MSET and MGET: set or retrieve the value of multiple keys in a single command

Query

The EXISTS command returns 1 or 0 to signal if a given key exists or not in the database.
The DEL command deletes a key and associated value, whatever the value is.
The TYPE command returns the kind of value stored at the specified key.

> set mykey hello
OK
> exists mykey
(integer) 1
> type mykey
string
> del mykey
(integer) 1
> exists mykey
(integer) 0
> type mykey
none

Expires: keys with limited time to live

When the time to live elapses, the key is automatically destroyed, exactly as if the user called the DEL command with the key.

  • They can be set both using seconds or milliseconds precision.
  • However the expire time resolution is always 1 millisecond.
  • Redis saves the date at which a key will expire.

The PERSIST can be used in order to remove the expire and make the key persistent forever.
The TTL check the remaining time to live for the key.

Set and check expires in milliseconds: PEXPIRE and PTTL.

Lists

Redis lists are implemented via Linked Lists.

  • LPUSH : adds a new element into a list, on the left (at the head)
  • LPOP : removes head.
  • RPUSH : adds a new element into a list ,on the right (at the tail)
  • RPOP : removes tail.
  • LRANGE : extracts ranges of elements from lists
> rpush mylist A
(integer) 1
> rpush mylist B
(integer) 2
> lpush mylist first
(integer) 3
> lrange mylist 0 -1
1) "first"
2) "A"
3) "B"

You are free to push multiple elements into a list in a single call: rpush mylist 1 2 3 4 5 "foo bar"

LTRIM: sets this range as the new list value. All the elements outside the given range are removed.

Example:

> rpush mylist 1 2 3 4 5
(integer) 5
> ltrim mylist 0 2
OK
> lrange mylist 0 -1
1) "1"
2) "2"
3) "3"

Use lists as a capped collection, only remembering the latest N items and discarding all the oldest items(by LPUSH and LTRIM):

LPUSH mylist <some element>
LTRIM mylist 0 999

Blocking operations:
BRPOP and BLPOP which are versions of RPOP and LPOP able to block if the list is empty: they'll return to the caller only when a new element is added to the list, or when a user-specified timeout is reached.

Example:

> brpop tasks 5
1) "tasks"
2) "do_something"

Build safer queues or rotating queues: RPOPLPUSH removes the last element (tail) of the list stored at source, and pushes the element at the first element (head) of the list stored at destination.

Hashes

  • HMSET sets multiple fields of the hash
  • HGET retrieves a single field
  • HMGET returns an array of values:

Example:

> hmset user:1000 username antirez birthyear 1977 verified 1
OK
> hget user:1000 username
"antirez"
> hget user:1000 birthyear
"1977"
> hgetall user:1000
1) "username"
2) "antirez"
3) "birthyear"
4) "1977"
5) "verified"
6) "1"
> hmget user:1000 username birthyear no-such-field
1) "antirez"
2) "1977"
3) (nil)

Other operations on individual fields:

  • HDEL
  • EXISTS
  • HINCRBY
  • HINCRBYFLOAT
  • HLEN

Sets

Redis Sets are unordered collections of strings.

  • SADD adds new elements to a set.
  • SMEMBERS Get all the members in a set (because set haven't method like RANGE)
  • SISMEMBER
  • SPOP Remove and return a random member from a set
  • SRANDMEMBER Get one or multiple random members from a set
  • SUNION Add multiple sets
  • SUNIONSTORE
  • SINTER Intersect multiple sets
  • SINTERSTORE
  • SCARD Get the number of members in a set

Sorted sets

Like sets, sorted sets are composed of unique, non-repeating string elements.

base

  • ZADD
  • ZCARD
  • ZINCRBY

count

  • ZCOUNT
  • ZLEXCOUNT Count the number of members in a sorted set between a given lexicographical range

range

  • ZRANGE Return a range of members in a sorted set, by index
  • ZREVRANGE
  • ZRANGEBYLEX Return a range of members in a sorted set, by lexicographical range
  • ZREVRANGEBYLEX
  • ZRANGEBYSCORE Return a range of members in a sorted set, by score
  • ZREVRANGEBYSCORE

check if is member of a set

  • ZRANK: Determine the index of a member in a sorted set.
  • ZREVRANK

remove

  • ZREM Remove one or more members from a sorted set
  • ZREMRANGEBYLEX Remove all members in a sorted set within the given lexicographical range
  • ZREMRANGEBYRANK
  • ZREMRANGEBYSCORE

2 ways to check if a member is in one key

  • ZRANK: Determine the index of a member in a sorted set.
  • ZREVRANK
  • ZSCORE: Get the score associated with the given member in a sorted set

set operation

  • ZINTERSTORE
  • ZUNIONSTORE

Bitmaps

Bitmaps are a set of bit-oriented operations defined on the String type.

  1. binary safe
  2. maximum length is 512 MB
  3. up to 232 different bits
  • SETBIT
  • GETBIT
  • BITCOUNT reporting the number of bits set to 1.
  • BITPOS Find first bit set or clear in a string
  • BITOP bitwise operation between multiple keys: AND, OR, XOR and NOT