Stream entry IDs in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Stream entry ID in Redis Streams?

A Stream entry ID is a unique identifier for each message in a Redis Stream. It consists of two parts: a timestamp in milliseconds and a sequence number, formatted as <millisecondsTime>-<sequenceNumber>.

beginner

How does Redis generate Stream entry IDs if you don't specify one?

Redis automatically generates the ID using the current server time in milliseconds and a sequence number starting at 0 for entries created in the same millisecond.

intermediate

Why does the Stream entry ID have two parts: timestamp and sequence number?

The timestamp ensures ordering by time, and the sequence number handles multiple entries created in the same millisecond, making each ID unique and ordered.

intermediate

What happens if you provide a custom Stream entry ID when adding an entry?

You can specify a custom ID, but it must be greater than the last ID in the stream to keep the order. Otherwise, Redis will return an error.

beginner

Explain the format of a Stream entry ID with an example.

A Stream entry ID looks like '1657891234567-0'. Here, '1657891234567' is the timestamp in milliseconds, and '0' is the sequence number for entries created at that exact millisecond.

What are the two parts of a Redis Stream entry ID?

A Timestamp and sequence number

B User ID and timestamp

C Sequence number and user ID

D Timestamp and message content

A Redis Stream entry ID consists of a timestamp in milliseconds and a sequence number.

If multiple entries are added in the same millisecond, how does Redis ensure unique IDs?

A By rejecting entries added in the same millisecond

B By changing the timestamp format

C By using random numbers

D By adding a sequence number after the timestamp

Redis appends a sequence number to the timestamp to keep IDs unique within the same millisecond.

What happens if you try to add a stream entry with an ID smaller than the last entry's ID?

A Redis accepts it without error

B Redis returns an error

C Redis automatically updates the ID

D Redis deletes the last entry

Redis requires IDs to be strictly increasing; otherwise, it returns an error.

Which part of the Stream entry ID helps maintain the order of messages?

A Timestamp

B Sequence number

C Message content

D User ID

The timestamp part ensures messages are ordered by creation time.

What is the format of a Redis Stream entry ID?

A <sequence>-<timestamp>

B <user>-<timestamp>

C <timestamp>-<sequence>

D <timestamp>_<sequence>

The correct format is timestamp followed by a dash and then the sequence number.

Describe how Redis Stream entry IDs are structured and why they are designed that way.

Think about how Redis keeps messages unique and in order.

Explain what happens when you add a stream entry with a custom ID and what rules it must follow.

Consider the importance of ordering in streams.