Outbox pattern for reliable events in Microservices - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert an event into the outbox table within the same transaction.

Microservices

BEGIN TRANSACTION;
INSERT INTO orders (id, status) VALUES (123, 'created');
INSERT INTO outbox (event_type, payload) VALUES ('OrderCreated', [1]);
COMMIT;

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

A'{"orderId":123}'

B123

CNULL

Dorder_data

Attempts:

3 left

💡 Hint

Common Mistakes

Inserting NULL instead of event data.

Using a raw number instead of a JSON string.

Forgetting to insert the event in the same transaction.

The event payload must be a JSON string representing the event data. Here, we insert a JSON string with the order ID.

2fill in blank

medium

Complete the code to select unprocessed events from the outbox for publishing.

Microservices

SELECT id, event_type, payload FROM outbox WHERE processed = [1];

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

ATRUE

BNULL

C1

DFALSE

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting events where processed is TRUE (already processed).

Using NULL which does not filter correctly.

We select events that have not been processed yet, so processed should be FALSE.

3fill in blank

hard

Fix the error in the code that marks an event as processed after publishing.

Microservices

UPDATE outbox SET processed = [1] WHERE id = event_id;

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

AFALSE

BTRUE

C0

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Setting processed to FALSE or 0 after publishing.

Setting processed to NULL which is ambiguous.

After publishing, the event should be marked as processed = TRUE.

4fill in blank

hard

Fill both blanks to implement a retry mechanism that selects events with less than 5 attempts and marks them as processing.

Microservices

SELECT id FROM outbox WHERE processed = FALSE AND attempts [1] 5;
UPDATE outbox SET processing = TRUE WHERE id = [2];

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

A<

B>

C=

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '<' to filter attempts.

Using '!=' instead of '=' in the update statement.

We select events with attempts less than 5 and update the processing flag for a specific event id.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps event IDs to payloads for unprocessed events with attempts less than 3.

Microservices

events = {event['id']: event[[1]] for event in events_list if event[[2]] [3] 3 and event['processed'] == False}

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

Apayload

Battempts

C<

Dprocessed

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'processed' as the value instead of 'payload'.

Using '>' instead of '<' for attempts comparison.

The comprehension maps event IDs to their payloads, filters events with attempts less than 3 and not processed.