XREAD for reading entries in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Redis command XREAD do?

The XREAD command reads new entries from one or more Redis streams. It returns stream entries starting from a given ID.

beginner

How do you specify which streams to read from using XREAD?

You provide the XREAD command with the keyword STREAMS, followed by the stream names and the IDs from which to start reading.

intermediate

What does the ID $ mean when used with XREAD?

The ID $ means to read only new entries added after the command is called, ignoring existing entries.

intermediate

What happens if you use XREAD BLOCK 0?

The command will block (wait) indefinitely until a new entry arrives in the stream, then return it.

advanced

How can you read from multiple streams at once using XREAD?

You list multiple stream names after STREAMS and provide one ID per stream. XREAD returns entries from all those streams starting from the given IDs.

What does XREAD STREAMS mystream 0 do?

A Blocks forever without returning any entries.

B Reads only new entries added after the command runs.

C Deletes all entries from 'mystream'.

D Reads all entries from 'mystream' starting from the very first entry.

The ID 0 means start reading from the very first entry in the stream.

Which ID should you use with XREAD to get only new entries added after the command runs?

A 0

B $

C -

D *

The ID $ tells Redis to return only new entries added after the command is called.

What does the BLOCK option do in XREAD?

A Deletes entries after reading.

B Limits the number of entries returned.

C Waits for new entries if none are available.

D Reads entries in reverse order.

BLOCK makes XREAD wait for new entries if none are currently available.

How do you read from two streams named 's1' and 's2' starting from their latest entries?

A XREAD STREAMS s1 s2 $ $

B XREAD STREAMS s1 s2 0 0

C XREAD STREAMS s1 s2 * *

D XREAD STREAMS s1 s2 - -

Use $ for each stream to read only new entries added after the command runs.

What is the output format of XREAD?

A A list of entries with stream name, entry ID, and fields.

B A boolean indicating success.

C A count of entries read.

D A list of stream names only.

XREAD returns entries grouped by stream name, each with entry IDs and their field-value pairs.

Explain how to use XREAD to read new entries from a Redis stream named 'orders'.

Think about reading only new data and waiting for it.

Describe the difference between using ID '0' and '$' with XREAD.

Consider what entries exist before and after the command.