Maxmemory setting in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the maxmemory to 100 megabytes in Redis.

Redis

CONFIG SET maxmemory [1]

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

A100mbs

B100mb

C100mbps

D100m

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect unit abbreviations like 'mbs' or 'mbps'.

Omitting the unit entirely.

Redis accepts both 100mb and 100m for 100 megabytes. Other options are invalid units.

2fill in blank

medium

Complete the command to check the current maxmemory setting in Redis.

Redis

CONFIG GET [1]

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

Amemorymax

Bmaxmemory

Cmax_mem

Dmemory_max

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect parameter names like 'memorymax' or 'max_mem'.

The correct parameter name to get the maxmemory setting is maxmemory.

3fill in blank

hard

Fix the error in the command to set maxmemory to 256 megabytes.

Redis

CONFIG SET maxmemory [1]

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

A256mb

B256

C256m

D256mbs

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the unit or using incorrect units like 'mbs'.

The correct value must include the unit 'mb' or 'm' for megabytes. Just '256' or '256mbs' is invalid.

4fill in blank

hard

Fill both blanks to set maxmemory to 512 megabytes.

Redis

CONFIG SET [1] [2]

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

Amaxmemory

Ballkeys-lru

C512mb

Dmaxmemory-policy

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing parameter names and values in the wrong order.

Using incorrect units or parameter names.

To set maxmemory, use 'maxmemory' as the parameter and '512mb' as the value. The eviction policy is set separately.

5fill in blank

hard

Fill all three blanks to set maxmemory to 1 gigabyte, set eviction policy to volatile-lru, and verify the maxmemory setting.

Redis

CONFIG SET [1] [2]
CONFIG SET [3] volatile-lru
CONFIG GET maxmemory

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

Amaxmemory

B1gb

Cmaxmemory-policy

Dmemory-policy

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter names for eviction policy.

Using incorrect memory units.

First, set 'maxmemory' to '1gb'. Then set 'maxmemory-policy' to 'volatile-lru'. Finally, get the maxmemory value.

Practice

1. What does the maxmemory setting in Redis control?

easy

A. The maximum amount of memory Redis can use

B. The maximum number of clients connected

C. The maximum size of a single key

D. The maximum number of commands per second

Solution

1. Step 1: Understand the purpose of maxmemory

   The maxmemory setting limits how much memory Redis can use to avoid overloading the server.

2. Step 2: Compare options with this purpose

   Only the maximum amount of memory Redis can use matches this description, others relate to clients, keys, or commands, which are unrelated.

3. Final Answer:

   The maximum amount of memory Redis can use -> Option A

4. Quick Check:

   maxmemory limits Redis memory use [OK]

Hint: maxmemory always limits Redis memory size [OK]

Common Mistakes:

• Confusing maxmemory with client limits
• Thinking maxmemory limits key size
• Assuming maxmemory limits command rate

2. Which of the following is the correct syntax to set maxmemory to 512 megabytes using CONFIG SET in Redis?

easy

A. CONFIG SET maxmemory 512mb

B. CONFIG SET maxmemory 512MB

C. CONFIG SET maxmemory 512m

D. CONFIG SET maxmemory 512

Solution

1. Step 1: Recall Redis size suffix format

   Redis accepts size suffixes like KB, MB, GB in uppercase for memory settings.

2. Step 2: Check each option's suffix

   CONFIG SET maxmemory 512MB uses 'MB' uppercase which is correct; CONFIG SET maxmemory 512mb uses lowercase 'mb' which is invalid; CONFIG SET maxmemory 512m uses 'm' which is not recognized; CONFIG SET maxmemory 512 has no suffix, so it's bytes, not megabytes.

3. Final Answer:

   CONFIG SET maxmemory 512MB -> Option B

4. Quick Check:

   Use uppercase suffixes like MB for megabytes [OK]

Hint: Use uppercase suffixes like MB, GB for sizes [OK]

Common Mistakes:

• Using lowercase suffixes like mb
• Using incomplete suffix like m
• Omitting suffix and expecting megabytes

3. Given the command CONFIG SET maxmemory 1GB executed on a Redis server, what will be the effect?

medium

A. Redis will limit its memory usage to 1 gigabyte

B. Redis will allow unlimited memory usage

C. Redis will limit memory to 1 byte

D. Redis will throw a syntax error

Solution

1. Step 1: Interpret the command meaning

   The command sets maxmemory to 1GB, meaning Redis should limit memory use to 1 gigabyte.

2. Step 2: Validate the command syntax and effect

   The syntax is correct and Redis supports 'GB' suffix, so it will enforce the memory limit.

3. Final Answer:

   Redis will limit its memory usage to 1 gigabyte -> Option A

4. Quick Check:

   CONFIG SET maxmemory 1GB limits memory to 1GB [OK]

Hint: CONFIG SET maxmemory with GB limits memory to gigabytes [OK]

Common Mistakes:

• Thinking it sets unlimited memory
• Confusing bytes with gigabytes
• Expecting syntax error from correct command

4. You run CONFIG SET maxmemory 100mb on Redis but it returns an error. What is the likely cause?

medium

A. Redis does not support changing maxmemory at runtime

B. maxmemory must be set in bytes only, no suffix allowed

C. The value 100mb is too large for Redis

D. The suffix 'mb' is lowercase and invalid

Solution

1. Step 1: Check Redis suffix case sensitivity

   Redis requires uppercase suffixes like MB, GB for memory sizes.

2. Step 2: Analyze the error cause

   Using lowercase 'mb' causes syntax error; changing to 'MB' fixes it.

3. Final Answer:

   The suffix 'mb' is lowercase and invalid -> Option D

4. Quick Check:

   Use uppercase suffixes for memory sizes [OK]

Hint: Always use uppercase suffixes like MB, GB [OK]

Common Mistakes:

• Assuming maxmemory can't be changed at runtime
• Using lowercase suffix causing errors
• Thinking maxmemory only accepts bytes

5. You want Redis to use at most 2 gigabytes of memory and automatically evict keys when the limit is reached. Which two commands should you run?

hard

A. CONFIG SET maxmemory 2gb and CONFIG SET maxmemory-policy allkeys-random

B. CONFIG SET maxmemory 2GB and CONFIG SET maxmemory-policy noeviction

C. CONFIG SET maxmemory 2GB and CONFIG SET maxmemory-policy allkeys-lru

D. CONFIG SET maxmemory 2048 and CONFIG SET maxmemory-policy volatile-lru

Solution

1. Step 1: Set maxmemory to 2 gigabytes correctly

   Use CONFIG SET maxmemory 2GB with uppercase suffix for 2 gigabytes.

2. Step 2: Choose eviction policy that evicts keys automatically

   allkeys-lru evicts least recently used keys from all keys, enabling automatic eviction.

3. Step 3: Verify other options

   Lowercase '2gb' with allkeys-random uses invalid suffix and random eviction; 2GB with noeviction disables eviction; 2048 (bytes, not GB) with volatile-lru limits to tiny memory and only evicts expiring keys.

4. Final Answer:

   CONFIG SET maxmemory 2GB and CONFIG SET maxmemory-policy allkeys-lru -> Option C

5. Quick Check:

   Set maxmemory + allkeys-lru for eviction [OK]

Hint: Use uppercase GB and allkeys-lru for eviction [OK]

Common Mistakes:

• Using lowercase suffix like '2gb'
• Choosing noeviction policy
• Setting maxmemory without suffix
• Using volatile-lru when all keys need eviction