Redis 2

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 "[e-mail]" # Adds the key-value pair {email : [e-mail]} to the hashmap
HSET person phone_number "[phone]" # 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) "[e-mail]"
5) "phone_number"
6) "[phone]"

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.

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Common Interview Questions

1. What is the full meaning of Redis?: Redis stands for REmote DIctionary Server

2. 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

3. 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

4. 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

5. 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