Which DynamoDB attribute should be used as a partition key for well-distributed records?

DVA-C02 By islever Editorial Last updated

Short answer

A Username

Question

A company is releasing a new feature. Users can request early access to the new feature by using an application form. The company expects a surge of requests when the application form becomes available. Each request will be stored as an item in an Amazon DynamoDB table. Each item will contain the user's username, the submission date, and a validation status of UNVALIDATED. VALID, or NOT VALID. Each item also will contain the user's rating of the process on a scale of 1 to 5. Each user can submit one request. For the DynamoDB table, the developer must choose a partition key that will give the workload well-distributed records across partitions. Which DynamoDB attribute will meet these requirements?
  1. Username Correct Answer
  2. Submission date
  3. Validation status
  4. Rating of the process on a scale of 1 to 5

Key Takeaways

The core concept is choosing a partition key with high cardinality and uniqueness to avoid hot partitions; the common trap is selecting attributes with low cardinality like status or rating.

This question tests the selection of an optimal DynamoDB partition key to ensure even data distribution across partitions during high-traffic surges. Community consensus strongly favors Username due to its high cardinality and uniqueness.

Common mistake: Candidates often mistakenly choose Submission date, thinking it has many distinct values, but simultaneous submissions during a surge can still cause hot partitions.

Expert Analysis

Understanding DynamoDB Partition Keys

In Amazon DynamoDB, the partition key (also known as the hash key) is critical for distributing data evenly across partitions. A well-chosen partition key ensures that the workload is spread out, preventing hot partitions that can degrade performance.

Why Username is the Correct Choice

Username is the best partition key because it is inherently unique for each user. Since each user can submit only one request, the username provides high cardinality and ensures that data is distributed evenly across partitions. This avoids the risk of hot partitions, even during a surge of requests.

Why Other Options Fail

  • Submission date (Option B): While it may seem to have many distinct values, submissions during a surge often occur at the same time, leading to concentrated data in specific partitions. This creates hot partitions.
  • Validation status (Option C): This attribute has only three possible values (UNVALIDATED, VALID, NOT VALID), resulting in extremely low cardinality. Most data would be concentrated in just a few partitions.
  • Rating of the process (Option D): With only five possible values (1 to 5), this attribute also has very low cardinality, making it unsuitable as a partition key.

Community Insights

The community overwhelmingly agrees that Username is the correct answer. As one user noted, "Username avoids a hot partition key," while another emphasized that the other options "are not even distributed." These insights reinforce the importance of selecting attributes with high cardinality and uniqueness for partition keys.

Key Takeaways

  • Always choose a partition key with high cardinality and uniqueness to ensure even data distribution.
  • Avoid attributes with low cardinality, such as status or rating, as they lead to hot partitions.
  • Consider the workload pattern (e.g., surges) when selecting a partition key.

Official Reference

https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/HowItWorks.CoreComponents.html#HowItWorks.CoreComponents.PrimaryKey

This link opens the official vendor documentation in a new tab.

Exam Strategy

When selecting a partition key, prioritize attributes with high cardinality and uniqueness. Eliminate options with low cardinality (e.g., status, rating) or attributes that may cluster during peak traffic (e.g., submission date).

Community Votes

A
100%

100% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 7 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 7

  1. Dzok5050 👍 5 Answered A
    It's A of course. This question got me wondering, who choses default right answers here
  2. nder 👍 3 Answered A
    Username avoids a hot partition key
  3. Saurabh04 👍 1 Answered B
    The submission date could be a good choice if it has high cardinality (many distinct values). However, if multiple requests occur simultaneously (e.g., during the surge), it might still lead to hot partitions
  4. Saudis 👍 1 Answered A
    partition key should be Unique so the A is a best choice
  5. CrescentShared 👍 2 Answered A
    rest is not even distributed.
Show 2 more comments
  1. 65703c1 👍 2 Answered A
    A is the correct answer.
  2. KarBiswa 👍 1 Answered A
    Username beyond doubt

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