Why streams handle event logs in Redis - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why are Redis Streams suitable for event logs?

Which of the following best explains why Redis Streams are a good choice for handling event logs?

A Because Redis Streams automatically delete old events without any configuration.

B Because Redis Streams store data in a relational table format for easy querying.

C Because Redis Streams store events in an ordered, append-only log that supports efficient reading and trimming.

D Because Redis Streams require manual indexing of each event to maintain order.

💡 Hint

Think about how event logs need to keep events in order and allow new events to be added efficiently.

Redis Streams keep events in an ordered, append-only structure which is perfect for event logs. They allow efficient reading and trimming, making them ideal for this use case.

❓ query_result

intermediate

Output of adding events to a Redis Stream

What is the output of the following Redis command sequence?

XADD mystream * event "login" user "alice"
XADD mystream * event "logout" user "bob"
XRANGE mystream - +

A [["1-0", {"event": "login", "user": "alice"}], ["2-0", {"event": "logout", "user": "bob"}]]

B SyntaxError: XRANGE requires a stream key

C [["1609459200000-0", {"event": "login", "user": "alice"}], ["1609459200001-0", {"event": "logout", "user": "bob"}]]

D []

💡 Hint

Redis assigns incremental IDs starting from 1-0 if you use * for the ID.

Using * in XADD generates IDs like 1-0, 2-0, etc. XRANGE returns all entries in order.

📝 Syntax

advanced

Identify the syntax error in Redis Stream command

Which option contains a syntax error when adding an event to a Redis Stream?

XADD mystream * event login user alice

A XADD mystream * event:login user:alice

B XADD mystream * event "login" user "alice"

C XADD mystream * event='login' user='alice'

D XADD mystream * event login user alice

💡 Hint

Check how field-value pairs should be formatted in XADD.

Redis expects field and value as separate arguments. Option D misses quotes around values, causing a syntax error.

❓ optimization

advanced

Best practice to limit Redis Stream size for event logs

Which Redis command option is best to limit the size of a stream to avoid unbounded growth when handling event logs?

A XADD mystream MINLEN 1000 * event "click" user "john"

B XADD mystream MAXLEN ~ 1000 * event "click" user "john"

C XADD mystream MAXLEN 1000 * event "click" user "john"

D XADD mystream TRIMLEN 1000 * event "click" user "john"

💡 Hint

Consider approximate trimming to improve performance.

Using MAXLEN ~ 1000 trims the stream approximately to 1000 entries, which is efficient and prevents unbounded growth.

🔧 Debug

expert

Why does this Redis Stream consumer fail to read new events?

A consumer uses XREAD with the ID '0' to read new events from a stream but never receives any new data. Why?

XREAD BLOCK 0 STREAMS mystream 0

A Because ID '0' reads from the beginning and blocks until new events after '0' arrive, but no new events are added.

B Because the BLOCK 0 option causes an immediate timeout, so no data is returned.

C Because the stream key 'mystream' does not exist, so XREAD fails silently.

D Because the ID '0' is invalid and causes a syntax error.

💡 Hint

Think about how XREAD uses IDs to read new events and how blocking works.

ID '0' means read from the very start, but if the consumer blocks waiting for events after '0' and no new events are added, it will wait indefinitely.