Atomic operations with Lua in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the Lua script to increment a Redis key atomically.

Redis

redis.call('[1]', KEYS[1])

Drag options to blanks, or click blank then click option'

Adel

Bget

Cincr

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'get' instead of 'incr' returns the value but does not increment.

Using 'set' overwrites the value instead of incrementing.

The incr command increments the integer value of a key by one atomically.

2fill in blank

medium

Complete the Lua script to set a key only if it does not exist.

Redis

redis.call('[1]', KEYS[1], ARGV[1])

Drag options to blanks, or click blank then click option'

Asetnx

Bgetset

Cset

Ddel

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set' overwrites the key regardless of existence.

Using 'getset' replaces the value and returns the old one.

The setnx command sets the key only if it does not already exist, ensuring atomicity.

3fill in blank

hard

Fix the error in the Lua script to decrement a key's value atomically.

Redis

redis.call('[1]', KEYS[1])

Drag options to blanks, or click blank then click option'

Aincr

Bdecr

Cdel

Dexpire

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'incr' increases the value instead of decreasing.

Using 'del' deletes the key instead of decrementing.

The decr command atomically decrements the integer value of a key by one.

4fill in blank

hard

Fill both blanks to atomically add a member to a set and set an expiration time.

Redis

redis.call('[1]', KEYS[1], ARGV[1])
redis.call('[2]', KEYS[1], tonumber(ARGV[2]))

Drag options to blanks, or click blank then click option'

Asadd

Bexpire

Cset

Ddel

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set' instead of 'sadd' overwrites the key.

Using 'del' removes the key instead of setting expiration.

sadd adds a member to a set atomically, and expire sets the key's time to live.

5fill in blank

hard

Fill all three blanks to atomically increment a hash field, check its value, and delete the key if zero.

Redis

local newVal = redis.call('[1]', KEYS[1], ARGV[1], 1)
if newVal == tonumber('[2]') then
  redis.call('[3]', KEYS[1])
end

Drag options to blanks, or click blank then click option'

Ahincrby

B0

Cdel

Dhset

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'hset' instead of 'hincrby' does not increment.

Comparing to '1' instead of '0' causes wrong deletion logic.

hincrby increments a hash field atomically, then we check if the value is zero, and del deletes the key if so.