Redis

Question 1

What happens when redis server gets turned off?

Answer 1

• The first method is a point-in-time dump either when certain conditions are met ( For example makes snapshot only if something was written during 15 minutes )
• The second method uses an append-only file that writes every command that alters data
  in Redis to disk as it happens.

Question 2

What real cases can redis improve comparing to relational DB?

Answer 2

• you can avoid writing unnecessary temporary data, avoid needing to scan over and delete this temporary data, and ultimately improve performance.
• Write statistics
• Counters
• Write logs

Question 3

What 5 redis data structure exists?

Answer 3

STRINGs, LISTs, SETs, HASHes, and ZSETs (sorted set)

Question 4

How to add/get/remove string value in redis?

Answer 4

set mykey ‘hello’
get mykey
del mykey

Question 5

How to get/add/remove values from the redis list?

Answer 5

rpush my_list 1 2 3
lindex my_list 0 # 1
lrange my_list 0 2 # 1 2 3
lpop my_list # removes first value from the left
rpop my_list # removes first value from the right

Question 6

How to get/add/remove values from the redis set?

Answer 6

sadd my_set 1
sadd my_set 2
sadd my_set 3
srem my_set 3
smembers my_set # 1 2
sismember my_set 32 # 0

Question 7

How to get/add/remove values from the redis hash?

Answer 7

hset my_hash key 12
hset my_hash key2 12
hget my_hash key
hdel my_hash key
hgetall my_hash # returns all

Question 8

How to implement pub/sub in redis?

Answer 8

SUBSCRIBE channel

PUBLISH channel ‘Hello message’

Question 9

How to use transaction in Redis?

Answer 9

MULTI
set key ‘hello’
….
EXEC

Question 10

What is snapshot drawback?

Answer 10

• Snaphot creating could stop the redis for several seconds if there too much data inside.