XLEN for stream length in Redis - Step-by-Step Execution

Concept Flow - XLEN for stream length

Start

↓

Send XLEN command with stream key

↓

Redis checks if stream exists

Yes No↓

Count entries

↓

Return count

↓

End

The XLEN command asks Redis for the number of entries in a stream. Redis checks if the stream exists, returns the count if yes, or 0 if no.

Execution Sample

Redis

XLEN mystream

# Returns the number of entries in 'mystream'

This command returns how many entries are in the Redis stream named 'mystream'.

Execution Table

Step	Action	Stream Exists?	Count Entries	Output
1	Send XLEN mystream	Unknown	N/A	N/A
2	Check if 'mystream' exists	Yes	N/A	N/A
3	Count entries in 'mystream'	Yes	3	N/A
4	Return count	Yes	3	3
5	End	N/A	N/A	N/A

💡 Execution stops after returning the count of entries in the stream.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
stream_exists	Unknown	Yes	Yes	Yes	Yes
entry_count	N/A	N/A	3	3	3
output	N/A	N/A	N/A	3	3

Key Moments - 2 Insights

What happens if the stream does not exist when XLEN is called?

If the stream does not exist, Redis returns 0 as the length. This is shown by the 'No' branch in the concept flow and would be reflected in the execution table if the stream_exists variable was 'No'.

Does XLEN return the actual entries or just the count?

XLEN returns only the count of entries, not the entries themselves. The execution table shows the output as a number, not the stream data.

Visual Quiz - 3 Questions

Look at the execution table, what is the output at Step 4?

A N/A

B 3

C 0

D Error

💡 Hint

Check the 'Output' column in Step 4 of the execution_table.

At which step does Redis confirm the stream exists?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Stream Exists?' column in the execution_table.

If the stream 'mystream' did not exist, what would XLEN return?

A The number of entries

B An error message

C 0

D Null

💡 Hint

Refer to the concept_flow where the 'No' branch returns 0.

Concept Snapshot

XLEN <stream_key>
Returns the number of entries in the Redis stream.
If the stream does not exist, returns 0.
Used to quickly check stream length without fetching entries.

Full Transcript

The XLEN command in Redis returns the length of a stream by counting its entries. When you send XLEN with a stream key, Redis first checks if the stream exists. If it does, Redis counts the entries and returns that number. If the stream does not exist, Redis returns 0. This lets you know how many entries are in the stream without retrieving the data itself.