Why Lua scripts enable atomicity in Redis - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a Lua script in Redis that runs atomically.

Redis

[1] "return redis.call('SET', 'key', 'value')" 0

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AEVAL

BEXEC

CCALL

DMULTI

Attempts:

3 left

💡 Hint

Common Mistakes

Using MULTI or EXEC instead of EVAL for Lua scripts.

The EVAL command runs Lua scripts atomically in Redis.

2fill in blank

medium

Complete the code to return a value from a Lua script in Redis.

Redis

return redis.call([1], 'GET', 'key')

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AEXISTS

BSET

CDEL

DGET

Attempts:

3 left

💡 Hint

Common Mistakes

Using SET instead of GET to retrieve a value.

The GET command retrieves the value of a key in Redis.

3fill in blank

hard

Fix the error in the Lua script to ensure atomic execution.

Redis

redis.call('SET', 'counter', redis.call([1], 'INCR', 'counter'))

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AGET

BINCR

CDEL

DSET

Attempts:

3 left

💡 Hint

Common Mistakes

Using GET or SET instead of INCR for incrementing.

The INCR command increments a counter atomically in Redis.

4fill in blank

hard

Fill both blanks to create a Lua script that atomically checks and sets a key.

Redis

if redis.call([1], 'EXISTS', 'lock') == 0 then
  redis.call([2], 'SET', 'lock', '1')
end

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AEXISTS

BSET

CGET

DDEL

Attempts:

3 left

💡 Hint

Common Mistakes

Using GET instead of EXISTS to check key presence.

The script checks if 'lock' exists and sets it if not, all atomically.

5fill in blank

hard

Fill all three blanks to write a Lua script that atomically increments a counter only if it exists.

Redis

if redis.call([1], 'EXISTS', 'counter') == 1 then
  return redis.call([2], 'INCR', 'counter')
else
  return redis.call([3], 'SET', 'counter', '1')
end

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

AEXISTS

BINCR

CSET

DDEL

Attempts:

3 left

💡 Hint

Common Mistakes

Using DEL instead of SET to initialize the counter.

This script checks if 'counter' exists, increments it if yes, or sets it to 1 if no, all atomically.