Redis and Memcached are both open-source, in-memory key-value data stores used for caching, but they differ in features and use cases. Redis stores data in memory and can persist to disk, supports data types beyond strings like lists and sets, and allows replication. Memcached only stores data in memory and does not support persistence or replication. While both are fast, Redis is more full-featured but requires more memory, making Memcached better for simple caching use cases with high traffic.

1. By Gaurav Agrawal
Redis Vs Memcached
Memcached or Redis? It's a question that nearly always arises in any discussion
about squeezing more performance out of a modern, database-driven Web
application. When performance needs to be improved, caching is often the first
step employed, and Memcached and Redis are typically the first places to turn.
Redis and Memcached
Redis
The name Redis means REmote DIctionary Server. Redis is an open source,
BSD licensed, advanced key-value store. It is often referred to as a data
structure server since keys can contain strings, hashes, lists, sets and sorted
sets. Redis is written in c.
Redis is an open source, advanced key-value store and a serious solution
for building high-performance, scalable web applications.
Redis has three main peculiarities that set it apart from much of its
competition:
 Redis holds its database entirely in memory, using the disk only for persistence.
 Redis has a relatively rich set of data types when compared to many key-value
data stores.
 Redis can replicate data to any number of slaves.
Memcached
Memcached is an open source, high-performance, distributed memory
caching system intended to speed up dynamic web applications by reducing
the database load. It is a key-value dictionary of strings, objects, etc,

2. By Gaurav Agrawal
stored in the memory, resulting from database calls, API calls, or page
rendering.
Memcached was developed by Brad Fitzpatrick for LiveJournal in 2003.
However, it is now being used by Netlog, Facebook, Flickr, Wikipedia,
Twitter, and YouTube among others.
The key features of Memcached are as follows −
 It is open source.
 Memcached server is a big hash table.
 It significantly reduces the database load.
 It is perfectly efficient for websites with high database load.
 It is distributed under Berkeley Software Distribution (BSD) license.
 It is a client-server application over TCP and/or UDP.
Memcached is not −
 a persistent data store
 a database
 application-specific
 a large object cache
 fault-tolerant or
 highly available
Redis vs Memcached
Similarities
 Both Memcached and Redis are in-memory.
 key-value data stores.
 They both belong to the NoSQL family.

3. By Gaurav Agrawal
 Both are based on the same key-value data model.
 They both keep all data in RAM, which makes them useful as a caching
layer.
 In terms of performance, the two data stores are also remarkably similar,
exhibiting almost identical characteristics (and metrics) with respect to
throughput and latency.
Differences
The main differences between them are listed below:
Installation:
Comparing ease of Installation Redis is much easier. No dependencies required.
Memory Usage:
For simple key-value pairs memcached is more memory efficient than Redis. If
you use Redis hashes, then Redis is more memory efficient.
Persistence:
If you are using Memcached then data is lost with a restart and rebuilding cache
is a costly process. On the other hand, Redis can handle persistent data. By
default, Redis syncs data to the disk at least every 2 seconds.
Replication:

4. By Gaurav Agrawal
Memcached does not supports replication. Whereas Redis supports master-slave
replication. It allows slave Redis servers to be exact copies of master servers.
Data from any Redis server can replicate to any number of slaves.
Storage type:
Memcached stores variables in it’s memory. It retrieve any information directly
from the servers memory instead of hitting the database again. On the other
hand, Redis is like a database that resides in memory. It executes (read and
write) a key/value pair from its database to return the resultset and all data
resides in memory. Developers are using Redis also for real-time metrics,
analytics.
Read/Write Speed:
Memcached is very good to handle high traffic websites. It can read lots of
information at a time and give you back at a great response time. Redis can
also handle high traffic on read but also can handle heavy writes as well.
Data Structure:
Memcached uses string and integer as data structure. Everything you save can
be either one or the other. With integer, the only data manipulation you can do
is adding or subtracting them. If you need to save arrays or objects, you will
have to serialize them first and then save them. To read them back, you will
need to un-serialize.
In comparison Redis has a stronger data structures. It can handle not only
strings, integer but also binary-safe strings, lists of binary-safe strings, sets of
binary-safe strings and sorted sets.
Key Length:
Memcached key length has a maximum of 250 bytes, whereas Redis key length
has a maximum of 2GB.
Redis can be used as a memcached on steroids because is as fast as
memcached but with a number of features more. Like memcached, Redis also
supports setting timeouts to keys so that this key will be automatically removed
when a given amount of time passes.

5. By Gaurav Agrawal
So, If you need advanced data structures or disk-backed persistence, you
should look into Redis. On the other hand, you might want to stick to
Memcached for its simplicity, reliability and speed.