[Solved] Identify the bug in this idempotent event consumer pseudocode: processed = set() def consume(event): processed.add(event.id) if event.id in processed: return process_event(event) | Microservices

Microservices - Event-Driven Architecture

Identify the bug in this idempotent event consumer pseudocode:

processed = set()
def consume(event):
    processed.add(event.id)
    if event.id in processed:
        return
    process_event(event)

AEvent ID is never added to the processed set

BThe processed set is cleared after each event

Cprocess_event is called before checking duplicates

DEvent ID is added before checking duplicates, so processing is skipped always

Step-by-Step Solution

Solution:

Step 1: Analyze the order of operations
The event ID is added to the processed set before the duplicate check.
Step 2: Understand the effect on duplicate check
Since the ID is always in the set, the check always returns true and processing is skipped.
Final Answer:
Event ID is added before checking duplicates, so processing is skipped always -> Option D
Quick Check:
Check must come before add [OK]

Quick Trick: Check duplicates before adding event ID [OK]

Common Mistakes:

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