RDB configuration (save intervals) in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set Redis to save the DB every 900 seconds if at least 1 key changed.

Redis

save [1] 1

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

A900

B300

C60

D1800

Attempts:

3 left

💡 Hint

Common Mistakes

Using the number of keys changed as the first number instead of the second.

Confusing seconds with minutes.

The save directive uses seconds and number of changes. Here, 900 seconds means 15 minutes.

2fill in blank

medium

Complete the code to save the DB every 300 seconds if at least 10 keys changed.

Redis

save [1] 10

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

A900

B600

C60

D300

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the two numbers.

Using 10 as the time interval.

The first number is the time in seconds, here 300 seconds means 5 minutes.

3fill in blank

hard

Fix the error in the save configuration to save every 60 seconds if 100 keys changed.

Redis

save [1] 100

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

A10

B60

C100

D600

Attempts:

3 left

💡 Hint

Common Mistakes

Using the number of keys changed as the first number.

Using 100 as the time interval.

The first number must be the time in seconds, so 60 means 1 minute.

4fill in blank

hard

Fill both blanks to save every 1800 seconds if at least 5 keys changed.

Redis

save [1] [2]

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

A1800

B5

C10

D900

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the two numbers.

Using 10 instead of 5 for keys changed.

The first number is the time in seconds (1800 = 30 minutes), the second is the minimum keys changed (5).

5fill in blank

hard

Fill all three blanks to configure Redis to save every 900 seconds if 1 key changed, every 300 seconds if 10 keys changed, and every 60 seconds if 100 keys changed.

Redis

save [1] 1
save [2] 10
save [3] 100

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

A60

B300

C900

D120

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the time intervals.

Using 120 seconds which is not part of the requirement.

The save intervals are 900 seconds for 1 key, 300 seconds for 10 keys, and 60 seconds for 100 keys.

Practice

1. What does the Redis save configuration option control?

easy

A. The port Redis listens on

B. The maximum memory Redis can use

C. When Redis automatically saves snapshots of the dataset

D. The password required to connect to Redis

Solution

1. Step 1: Understand the purpose of save in Redis

   The save option defines intervals for automatic snapshot saving.

2. Step 2: Identify what save controls

   It controls when Redis saves data snapshots based on time and changes.

3. Final Answer:

   When Redis automatically saves snapshots of the dataset -> Option C

4. Quick Check:

   RDB save intervals = automatic snapshot timing [OK]

Hint: Remember: save sets snapshot save timing [OK]

Common Mistakes:

• Confusing save with memory limits
• Thinking save sets connection ports
• Assuming save controls authentication

2. Which of the following is the correct syntax to save Redis data every 300 seconds if at least 10 keys changed?

easy

A. save 10 300

B. save 300 10

C. save 300,10

D. save 10;300

Solution

1. Step 1: Recall Redis save syntax

   The syntax is save <seconds> <changes> without commas or semicolons.

2. Step 2: Match the correct order

   Time in seconds comes first, then number of changes.

3. Final Answer:

   save 300 10 -> Option B

4. Quick Check:

   Correct syntax = save seconds changes [OK]

Hint: Syntax is: save seconds changes (space separated) [OK]

Common Mistakes:

• Swapping seconds and changes order
• Using commas or semicolons instead of spaces
• Omitting one of the two required values

3. Given the Redis config lines:
save 900 1
save 300 10
What happens if 5 keys change within 400 seconds?

medium

A. Redis does not save a snapshot because 10 changes were not reached

B. Redis saves a snapshot after 300 seconds because 10 changes are needed

C. Redis saves a snapshot immediately after 5 changes

D. Redis saves a snapshot after 900 seconds because 1 change triggers it

Solution

1. Step 1: Analyze each save interval

   First interval: save every 900 seconds if at least 1 change.
   Second interval: save every 300 seconds if at least 10 changes.

2. Step 2: Check conditions for 5 changes in 400 seconds

   5 changes < 10, so second interval not triggered.
   900 seconds not reached yet, so first interval not triggered either.

3. Final Answer:

   Redis does not save a snapshot because 10 changes were not reached -> Option A

4. Quick Check:

   5 changes in 400s does not meet any save condition [OK]

Hint: Check each interval separately for time and changes [OK]

Common Mistakes:

• Assuming 5 changes triggers 10-change interval
• Ignoring the time condition for the first interval
• Thinking Redis saves immediately after changes

4. You wrote this Redis config line:
save 60,5
Why does Redis ignore this setting?

medium

A. Because commas are invalid; spaces must separate values

B. Because 5 changes is too low to trigger saving

C. Because 60 is not a valid time value

D. Because save intervals must be in milliseconds

Solution

1. Step 1: Check syntax of save line

   Redis requires space-separated values, not commas.

2. Step 2: Understand why commas cause ignoring

   Commas make the line invalid, so Redis skips it.

3. Final Answer:

   Because commas are invalid; spaces must separate values -> Option A

4. Quick Check:

   Use spaces, not commas in save intervals [OK]

Hint: Use spaces, never commas, between save parameters [OK]

Common Mistakes:

• Thinking commas are allowed separators
• Believing time must be in milliseconds
• Assuming low changes disables saving

5. You want Redis to save a snapshot if either:
- 5 keys changed in 60 seconds
- OR 100 keys changed in 900 seconds
Which configuration lines achieve this?

hard

A. save 900 5\nsave 60 100

B. save 5 60\nsave 100 900

C. save 60 100\nsave 900 5

D. save 60 5\nsave 900 100

Solution

1. Step 1: Match time and changes correctly

   Format is save <seconds> <changes>.
   So 60 seconds and 5 changes is save 60 5.
   900 seconds and 100 changes is save 900 100.

2. Step 2: Verify both conditions are separate lines

   Each condition must be on its own save line.

3. Final Answer:

   save 60 5 save 900 100 -> Option D

4. Quick Check:

   Time first, changes second per line [OK]

Hint: Write each interval on its own line: save seconds changes [OK]

Common Mistakes:

• Swapping seconds and changes
• Putting both intervals on one line
• Using commas or semicolons instead of spaces