Redis - Lists, Sets and HashMaps
This is a continuation to the previous blogpost
There are 3 other data types available apart from key-value pairs
Lists
This data structure resembles the list in Python or the array in Javascript or C#. They can be used to keep recently used items. The common operations are;
| Operations | Explanations | Examples | Further Explanation |
|---|---|---|---|
| LPUSH | Adds an Item to the beginning of the list | LPUSH friends "Sophia" |
similar to Array.unshift in javascript |
| LRANGE | Get all the items in a list | LRANGE friends 0 -1 |
similiarly a list in python 0 is the first item and -1 is the last item |
| RPUSH | Adds an item to the end of the list | RPUSH friends "Poe" |
similar to Array.push in javascript |
| LPOP | Removes an item from the start of the list | LPOP friends "Poe" |
Will return 1 if Poe exists in the list and 0 otherwise |
| RPOP | Removes an item from the end of the list | RPOP friends "Sophia" |
Will return 1 if Sophia exists in the list and 0 otherwise |
Sets
A data structure that only has unique items. similar to sets in Python and Sets in Javascript and HashSets in C#. Common operations include;
| Operations | Explanations | Examples | Further Explanation |
|---|---|---|---|
| SADD | Adds a value to the set | SADD colors "pink" |
|
| SMEMBERS | returns the members of the set | SMEMBERS colors |
will return all the items in the set colors |
| SREM | Removes members of the set | SREM colors "pink" |
Will return 1 if pink exists in the list and 0 otherwise |
Hashmaps
An hashmap is a group of key value pairs. An hashmap however cannot be nested. Lets take a case scenario of a person with a name, email and phone number
HSET person name "Joe" # Adds the key-value pair {name : joe} to the hashmap
HSET person email "Joe@joe.com" # Adds the key-value pair {email : Joe@joe.com} to the hashmap
HSET person phone_number "+2345656655413" # Adds the key-value pair {number : ....} to the hashmap
the HGET command can be used to get the value of a particular key in a hashmap
HGET person name # returns "Joe"
the HGETALL command all the key-value pair in the hashmap
HGETALL person
1) "name"
2) "Joe"
3) "email"
4) "Joe@joe.com"
5) "phone_number"
6) "+2345656655413"
the HDEL command deletes a key-value pair by its key
HDEL person name # removes {name : joe}
the HEXISTS command checks if a key exists in a hashset
HEXISTS person name # returns 0 because we've deleted it before
Those are most of the basic commands a developer is required to know.
Common Interview Questions
What is the full meaning of Redis?: Redis stands for REmote DIctionary Server
How does redis differ from traditional databases like MySQL?: Redis operates in main memory and have basic operations for accessing values quickly unlike SQL which resides on disk and has a wide range of crud operations
What are the limitations of Redis regarding data size and type?: Redis is designed to hold values that fits into the machines memory. It is not suitable for complex relational models with joins or for structuring large blobs
How do you handle caching in a distributed environment using Redis?: Handle caching by setting up redis instances as a caching layer in front of the database. using consistent hashing to distribute keys accreoss the cache nodes ensueres even load distribution and reduces cache misses
When should you use List data types in Redis?: Lists are great for durable atomic queues, for job queue, logs, buffers and many other use cases
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