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Kafkadevops~10 mins

Why delivery guarantees affect correctness in Kafka - Visual Breakdown

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Process Flow - Why delivery guarantees affect correctness
Message Produced
Delivery Guarantee Check
At Most Once
Possible Loss
Incorrect
Message Consumed
Application Correctness Depends on Guarantee
The flow shows how different delivery guarantees lead to different message outcomes, affecting correctness.
Execution Sample
Kafka
produce(message)
if guarantee == 'at_most_once':
    send_once()
elif guarantee == 'at_least_once':
    retry_until_ack()
else:
    transaction_commit()
This code sends a message with different delivery guarantees affecting retries and transactions.
Process Table
StepDelivery GuaranteeActionMessage OutcomeCorrectness Impact
1at_most_onceSend message once, no retryMessage may be lostPossible incorrect processing due to loss
2at_least_onceRetry sending until ack receivedMessage may be duplicatedPossible incorrect processing due to duplicates
3exactly_onceSend message within transactionMessage delivered once exactlyCorrect processing assured
4N/AMessage consumed by applicationOutcome depends on guaranteeCorrectness depends on guarantee
💡 Execution stops after message consumption; correctness depends on delivery guarantee chosen.
Status Tracker
VariableStartAfter Step 1After Step 2After Step 3Final
message_statusnot_sentsent_once_or_lostsent_with_possible_duplicatessent_once_transactionalfinal_state_based_on_guarantee
retry_attempts00>=10depends_on_guarantee
Key Moments - 3 Insights
Why can 'at_most_once' cause message loss?
Because it sends the message only once without retry, if the message is lost in transit, it is never resent (see execution_table row 1).
Why does 'at_least_once' risk duplicates?
Because it retries sending until acknowledged, duplicates can occur if the first send succeeded but ack was lost, causing resend (see execution_table row 2).
How does 'exactly_once' guarantee correctness?
It uses transactions to ensure the message is delivered once and only once, preventing loss and duplicates (see execution_table row 3).
Visual Quiz - 3 Questions
Test your understanding
Look at the execution_table, what is the message outcome at step 2 with 'at_least_once' guarantee?
AMessage may be duplicated
BMessage delivered once exactly
CMessage may be lost
DMessage not sent
💡 Hint
Check execution_table row 2 under 'Message Outcome'
According to variable_tracker, how many retry attempts happen after step 2?
A0
BExactly 1
CAt least 1
DDepends on transaction
💡 Hint
Look at 'retry_attempts' variable after step 2 in variable_tracker
If we change from 'at_most_once' to 'exactly_once', what changes in message_status after step 3?
AFrom 'not_sent' to 'sent_with_possible_duplicates'
BFrom 'sent_once_or_lost' to 'sent_once_transactional'
CNo change
DFrom 'sent_with_possible_duplicates' to 'sent_once_or_lost'
💡 Hint
Compare 'message_status' values in variable_tracker after steps 1 and 3
Concept Snapshot
Delivery guarantees in Kafka affect message correctness:
- at_most_once: send once, risk loss
- at_least_once: retry, risk duplicates
- exactly_once: transactional, no loss or duplicates
Choose guarantee based on correctness needs.
Full Transcript
This visual execution shows how Kafka delivery guarantees impact message correctness. The code example sends messages differently based on guarantee. The execution table traces steps for at_most_once, at_least_once, and exactly_once guarantees, showing message outcomes and correctness impact. Variable tracker follows message status and retry attempts. Key moments clarify why loss or duplicates happen. The quiz tests understanding of message outcomes and variable changes. The snapshot summarizes guarantees and their effects on correctness.