The answer is a consumer application crash and restart causing re-processing of records. This happens because the Kinesis Client Library (KCL) uses DynamoDB for checkpointing, recording the last successfully processed sequence number per shard. If the application crashes, the KCL resumes from the last committed checkpoint, not the most recently processed record. Any records processed after that checkpoint but before the crash will be re-processed, leading to duplicate processing. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of KCL’s at-least-once delivery semantics and the trade-off between checkpoint frequency and duplicate risk. A common trap is assuming DynamoDB throttling or shard splitting causes duplicates, but the core issue is always the gap between processing and checkpointing. Memory tip: think of checkpointing like saving a game—if you crash before saving, you replay from the last save point.
DEA-C01 Data Ingestion and Transformation Practice Question
This DEA-C01 practice question tests your understanding of data ingestion and transformation. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A financial services company processes real-time stock trade data. They use Amazon Kinesis Data Streams with a shard count of 5, each shard receiving about 500 records per second. The consumer application uses the Kinesis Client Library (KCL) with DynamoDB for checkpointing. Lately, some records are being processed multiple times. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The consumer application is crashing and restarting, causing re-processing of records.
The Kinesis Client Library (KCL) uses DynamoDB to track checkpoint progress for each shard. If the consumer application crashes and restarts, the KCL will resume processing from the last committed checkpoint, which may be behind the actual processing point. This causes records that were already processed (but not yet checkpointed) to be re-processed, leading to duplicate processing.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
The consumer application is crashing and restarting, causing re-processing of records.
Why this is correct
KCL reprocesses from last checkpoint after failure.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The Kinesis stream's iterator age is exceeding the retention period.
Why it's wrong here
Causes data loss, not duplicates.
✗
The DynamoDB table used for checkpointing is throttling write requests.
Why it's wrong here
Causes delays, not duplicates.
✗
The record size exceeds the 1 MB API limit, causing retries.
Why it's wrong here
Causes throttling, not duplicates.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse checkpoint throttling (Option C) with duplicate processing, but throttling would cause checkpoint failures and potential re-processing only if the application cannot recover, whereas the direct cause of duplicates is the gap between processing and checkpointing after a crash.
Detailed technical explanation
How to think about this question
KCL checkpointing is asynchronous and batched; by default, the KCL commits checkpoints every 60 seconds (configurable via `checkpointIntervalMillis`). If a consumer crashes between checkpoint commits, all records processed since the last checkpoint will be re-processed upon restart. This is a common trade-off between exactly-once and at-least-once processing semantics in distributed stream processing systems.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Data Ingestion and Transformation — This question tests Data Ingestion and Transformation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The consumer application is crashing and restarting, causing re-processing of records. — The Kinesis Client Library (KCL) uses DynamoDB to track checkpoint progress for each shard. If the consumer application crashes and restarts, the KCL will resume processing from the last committed checkpoint, which may be behind the actual processing point. This causes records that were already processed (but not yet checkpointed) to be re-processed, leading to duplicate processing.
What should I do if I get this DEA-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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