Transactions vs Lua scripts in Redis - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a Redis transaction.

Redis

redis.call('[1]')

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

AMULTI

BDISCARD

CWATCH

DEXEC

Attempts:

3 left

💡 Hint

Common Mistakes

Using EXEC to start a transaction instead of MULTI.

Using WATCH which is for monitoring keys, not starting transactions.

The MULTI command starts a Redis transaction block.

2fill in blank

medium

Complete the code to execute all commands queued in a Redis transaction.

Redis

redis.call('[1]')

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

AWATCH

BMULTI

CDISCARD

DEXEC

Attempts:

3 left

💡 Hint

Common Mistakes

Using MULTI instead of EXEC to run commands.

Using DISCARD which cancels the transaction.

The EXEC command executes all commands queued in the current transaction.

3fill in blank

hard

Fix the error in the Lua script to atomically increment a key and return its new value.

Redis

local newVal = redis.call('INCR', '[1]')
return newVal

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

AINCR

Bcounter

CMULTI

DEXEC

Attempts:

3 left

💡 Hint

Common Mistakes

Using command names like MULTI or EXEC as key names.

Leaving the key name blank or incorrect.

The key name to increment must be provided as a string, here 'counter'.

4fill in blank

hard

Fill both blanks to watch a key and start a transaction in Redis.

Redis

redis.call('[1]', 'mykey')
redis.call('[2]')

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

AWATCH

BMULTI

CEXEC

DDISCARD

Attempts:

3 left

💡 Hint

Common Mistakes

Using EXEC before MULTI.

Using DISCARD instead of MULTI.

WATCH monitors the key for changes, and MULTI starts the transaction.

5fill in blank

hard

Fill all three blanks to write a Lua script that increments a key only if it has not changed since watching it.

Redis

redis.call('[1]', KEYS[1])
redis.call('[2]')
redis.call('INCR', KEYS[1])
local val = redis.call('[3]')
return val[1]

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

AWATCH

BMULTI

CEXEC

DDISCARD

Attempts:

3 left

💡 Hint

Common Mistakes

Using DISCARD instead of EXEC.

Not watching the key before starting the transaction.

The script watches the key, starts a transaction, increments the key, then executes the transaction.