Types

Keys

Try to stick with a schema. For instance object-type:id is a good idea, as in "user:1000". Dots or dashes are often used for multi-word fields, as in comment:1234:reply.to or comment:1234:reply-to.

Hash

field and value form a pair. Both are strings

• If this were Javascript,
  • the object name would be the Redis key,
  • the object key would be the Redis field,
  • the object value would be the Redis value

user:1000: {
    "username": "antirez",
    "birthyear": 1970
}

Methods:

• HGET <key> <field> / HSET <key> <field> <value> - get/set a field+value

Lists

Redis lists are implemented via Linked Lists.

• LinkedLists were used (as opposed to arrays) because for a database system it is crucial to be able to add elements to a very long list in a very fast way.
• When fast access to the middle of a large collection of elements is important, Sorted Sets should be used

Common use-cases for Lists

• Remember the latest updates posted by users into a social network.
  • ex. Twitter takes the latest tweets posted by users into Redis lists.
  • imagine your home page shows the latest photos published in a photo sharing social network and you want to speedup access.
    • Every time a user posts a new photo, we add its ID into a list with LPUSH.
    • When users visit the home page, we use LRANGE 0 9 in order to get the latest 10 posted items.
• Communication between processes, using a consumer-producer pattern where the producer pushes items into a list, and a consumer (usually a worker) consumes those items and executed actions. Redis has special list commands to make this use case both more reliable and efficient.

Methods:

• LPUSH / RPUSH - add element to the left/right
• LRANGE <listname> <fromindex> <toindex> - extract ranges of elements from lists

Sets

A set is an unordered collections of unique strings (ie, a mathematical set (Private))

Sets are good for expressing relations between objects. For instance we can easily use sets in order to implement tags.

• A simple way to model this problem is to have a set for every object we want to tag. The set contains the IDs of the tags associated with the object.

Methods: SADD - add element to set

Most set operations, including adding, removing, and checking whether an item is a set member, are O(1) (highly efficient).

• except for SMEMBERS command, which is O(n) and returns the entire set in a single response

# Store a value in the set of favorite book IDs for user 123
> SADD user:123:favorites 742
(integer) 1

# Check whether user 123 likes book 742
> SISMEMBER user:123:favorites 742
(integer) 1

Sorted Sets

similar to a mix between a Set and a Hash

• Like sets, sorted sets are composed of unique, non-repeating string elements, so in some sense a sorted set is a set as well.
• every element in a sorted set is associated with a floating point value, called the score (this is why the type is also similar to a hash, since every element is mapped to a value).

Methods: ZADD - add element to set ZREVRANGE - Returns the specified range of elements in the sorted set stored at key

E Resources

Redis Documentation