Latest Redis Interview Questions

1) Explain what is Redis?

Redis is an advanced key-value data store and cache. It has also been referred as a data structure server as such the keys not only contains strings, but also hashes, sets, lists, and sorted sets. Companies using Redis includes Stackoverflow, Twitter, Github, etc.

2) Explain Replication feature of Redis?

Redis supports simple master to slave replication. When a relationship is established, data from the master is transferred to the slave. Once this is done, all changes to the master replicate to the slave

3) Mention what is the difference between Memcached and Redis?

Redis

Redis also does caching information but has got additional features like persistence and replication

Redis does not support the functionality of LRU (least recently used) eviction of values

In Redis you can set a time out on everything, when memory is full, it will look at three random keys and deletes the one which is closest to expiry

Redis does not support CAS ( Check and Set). It is useful for maintaining cache consistency

Redis has got stronger data structures; it can handle strings, binary safe strings, list of binary safe strings, sorted lists, etc.

Redis had a maximum of 2GB key length

Redis is single threaded

Memcached

Memcached only does caching information.

Memcached supports the functionality of LRU (least recently used) eviction of values

In Memcached when they overflow memory, the one you have not used recently (LRU- least recently used) will get deleted

Memcached supports CAS (Check and Set)

In Memcached, you have to serialize the objects or arrays in order to save them and to read them back you have to un-serialize them.

Memcached had a maximum of 250 bytes length

Memcached is a multi-threaded

4) Mention what are the advantages of using Redis?

Advantage of using Redis is

It provides high speed

It supports a server-side locking

It has got lots of client lib

It has got command level Atomic Operation (tx operation)

5) Mention what are the limitations of Redis?

It is single threaded

It has got limited client support for consistent hashing

It has significant overhead for persistence

It is not deployed widely

6) List out the operation keys of Redis?

Operation keys of Redis includes

TYPE key
TTL key
KEYS pattern
EXPIRE key seconds
EXPIREAT key timestamp
EXISTS key
DEL key

7) Which PHP module can be used with Redis?

With PHP module, PRedis is more preferable than Redid PHP binding or Resident

8) Does Redis gives speed and durability both?

No, Redis purposely compromise the durability to enhance the speed. In Redis, in the event of system failure or crash, Redis writes to disk but may fall behind and lose the data which is not stored.

9) How can you improve the durability in Redis?

To improve the durability of Redis “append only file” can be configured by using fsync data on disk.

Fsync () every time a new command is added to the append log file: It is safe but very slow

Fysnc() one time every second: It is fast, but you may lose 1 second of data if system fails

Never fsync(): It is an unsafe method, and your data is in hand of Operating System

10) Mention what are the things you have to take care while using Redis?

While using Redis one must take care of

Select a consistent method to name and prefix your keys. Manage your namespace
Create a “Registry” of key prefixes that maps each of your internal documents for those application which “own” them
For every class you put through into your Redis infrastructure : design, implement and test the mechanisms for garbage collection or data migration to archival storage
Design, implement and test a sharding library before you have invested much into your application deployment and make sure that you keep a registry of “shards “replicated on each server
Separate all your K/V store and related operations into your own library/API or service