XLEN for stream length in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the length of a Redis stream named 'mystream'.

Redis

XLEN [1]

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

Amystream

Bmylist

Cmyhash

Dmyset

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-stream key like a list or hash name.

Forgetting to provide the stream name after XLEN.

The XLEN command returns the number of entries in the specified stream. Here, the stream name is mystream.

2fill in blank

medium

Complete the code to get the length of a Redis stream stored in the variable 'stream_key'.

Redis

XLEN [1]

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

Astream_key

B'stream_key'

CstreamKey

DSTREAM_KEY

Attempts:

3 left

💡 Hint

Common Mistakes

Adding quotes around the variable name, making it a string literal.

Using uppercase or camelCase when the variable is lowercase.

When using a variable name in Redis CLI or scripts, use it directly without quotes. Here, stream_key is the variable holding the stream name.

3fill in blank

hard

Fix the error in the command to get the length of the stream 'events'.

Redis

XLEN [1]

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

Aevents_stream

Bevents

C'events'

Devent

Attempts:

3 left

💡 Hint

Common Mistakes

Adding quotes around the stream name.

Using a wrong or incomplete stream name.

The correct stream name is events without quotes. Using quotes causes a syntax error in Redis CLI.

4fill in blank

hard

Fill both blanks to get the length of the stream stored in variable 'streamName' and store it in variable 'length'.

Redis

length = [1] [2]

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

AXLEN

BstreamName

Cmystream

DGET

Attempts:

3 left

💡 Hint

Common Mistakes

Using GET instead of XLEN.

Using a hardcoded stream name instead of the variable.

Use XLEN followed by the stream variable streamName to get the stream length.

5fill in blank

hard

Fill all three blanks to get the length of the stream 'orders', check if it is greater than 100, and store the result in 'isLarge'.

Redis

length = [1] [2]
isLarge = length [3] 100

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

AXLEN

Borders

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong comparison operator.

Using a wrong stream name.

First, use XLEN orders to get the stream length. Then compare if length is greater than 100 using >.

Practice

1. What does the Redis command XLEN do when used on a stream key?

easy

A. Deletes the stream key

B. Returns the number of entries in the stream

C. Returns the last entry in the stream

D. Adds a new entry to the stream

Solution

1. Step 1: Understand the purpose of XLEN

   The XLEN command is designed to return the count of entries in a Redis stream.

2. Step 2: Compare with other commands

   Unlike commands that add or delete entries, XLEN only returns the length (number of entries).

3. Final Answer:

   Returns the number of entries in the stream -> Option B

4. Quick Check:

   XLEN = stream length count [OK]

Hint: XLEN always gives stream size count, not data content [OK]

Common Mistakes:

• Confusing XLEN with XADD which adds entries
• Thinking XLEN deletes or modifies the stream
• Assuming XLEN returns stream entries instead of count

2. Which of the following is the correct syntax to get the length of a Redis stream named mystream?

easy

A. XLEN = mystream

B. XLEN(mystream)

C. XLEN mystream

D. XLEN->mystream

Solution

1. Step 1: Recall Redis command syntax

   Redis commands use the format COMMAND key without parentheses or operators.

2. Step 2: Identify correct syntax

   XLEN mystream is the correct way to call the command to get stream length.

3. Final Answer:

   XLEN mystream -> Option C

4. Quick Check:

   Redis commands use space-separated syntax [OK]

Hint: Redis commands never use parentheses or operators [OK]

Common Mistakes:

• Using parentheses like a function call
• Trying to assign XLEN to a variable with =
• Using arrow or other operators in command

3. Given a Redis stream orders with 5 entries, what will the command XLEN orders return?

medium

A. 5

B. 0

C. An error

D. The last entry ID

Solution

1. Step 1: Understand what XLEN returns

   XLEN returns the number of entries in the stream, which is 5 here.

2. Step 2: Confirm no errors expected

   Since the stream exists and has entries, no error or zero is returned.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   XLEN counts entries = 5 [OK]

Hint: XLEN returns count, not content or errors if stream exists [OK]

Common Mistakes:

• Assuming XLEN returns zero if stream has entries
• Expecting XLEN to return entry data or IDs
• Thinking XLEN throws error for existing streams

4. You run XLEN mystream but get (integer) 0. What is the likely cause?

medium

A. Redis server is down

B. XLEN command is misspelled

C. XLEN cannot be used on streams

D. The stream mystream does not exist in Redis

Solution

1. Step 1: Understand XLEN behavior on missing keys

   XLEN returns (integer) 0 if the stream key does not exist or is empty.

2. Step 2: Check command correctness

   If command is correct and server is running, 0 indicates the stream mystream does not exist.

3. Final Answer:

   The stream mystream does not exist in Redis -> Option D

4. Quick Check:

   Missing key returns 0 from XLEN [OK]

Hint: XLEN returns 0 for missing or empty stream keys [OK]

Common Mistakes:

• Assuming XLEN command is wrong
• Ignoring server status or connection issues
• Thinking XLEN can't be used on streams

5. You want to monitor the size of a Redis stream events and alert if it exceeds 1000 entries. Which Redis command helps you check the stream length efficiently?

hard

A. XLEN events

B. XREAD events

C. XTRIM events MAXLEN 1000

D. XDEL events

Solution

1. Step 1: Identify command to get stream length

   XLEN returns the number of entries in a stream efficiently.

2. Step 2: Compare with other commands

   XREAD reads entries, XTRIM trims stream, XDEL deletes entries; none return length.

3. Final Answer:

   XLEN events -> Option A

4. Quick Check:

   Use XLEN to get stream size for monitoring [OK]

Hint: Use XLEN to get stream length quickly for alerts [OK]

Common Mistakes:

• Using XREAD which reads data, not length
• Using XTRIM which modifies stream instead of checking length
• Using XDEL which deletes entries