← DBS-C01·Amazon Web Services

Question 497 of 1,730

Workload-Specific Database Design →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is the default algorithm (COPY) used by ALTER TABLE, which locks the table and blocks writes, causing replication lag. When you add an index to a large MySQL table without specifying an algorithm, MySQL defaults to COPY, which creates a new table, copies all 200 million rows, and rebuilds indexes under a write lock. This blocks the 10,000 writes per second, increasing write latency on the primary, and in a Multi-AZ deployment, the same blocking DDL replicates to the standby, manifesting as replication lag. On the AWS Certified Database Specialty DBS-C01 exam, this tests your understanding of online DDL operations and the trade-offs between the COPY, INPLACE, and INSTANT algorithms—a common trap is assuming ALTER TABLE is always non-blocking. To avoid replication lag, always use ALGORITHM=INPLACE or LOCK=NONE for supported operations. Memory tip: “COPY locks, INPLACE rocks.”

DBS-C01 Workload-Specific Database Design Practice Question

This DBS-C01 practice question tests your understanding of workload-specific database design. 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 company runs a large-scale e-commerce platform using Amazon RDS for MySQL with a Multi-AZ deployment. The database has a table 'orders' with 200 million rows. Recently, they added a new index on the 'order_date' column to improve reporting queries. After adding the index, they noticed increased write latency and occasional replication lag. The application writes new orders continuously. The table experiences about 10,000 writes per second. The DB instance is db.r5.4xlarge. The index creation was done using the ALTER TABLE statement with a default algorithm. What is the most likely cause of the increased write latency and replication lag?

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.

Question 1hardmultiple choice

Full question →

A
The index creation DDL statement is not replicated to the standby instance, causing inconsistency.
Why wrong: DDL statements are replicated; the issue is the lock on the primary.
B
The instance size is insufficient for the write workload.
Why wrong: The instance is db.r5.4xlarge, which is typically sufficient for 10K writes/sec; the issue appeared after index creation.
C
The index was created using the default algorithm (COPY), which locks the table and blocks writes, causing replication lag.
In MySQL 5.6 and 5.7, ALTER TABLE uses COPY algorithm by default, which locks the table for writes during the operation.
D
The new index is causing excessive overhead on write operations due to index maintenance.
Why wrong: Index maintenance adds some overhead but not typically enough to cause significant latency and lag; the problem is the creation process.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The index was created using the default algorithm (COPY), which locks the table and blocks writes, causing replication lag.

Option C is correct because the default algorithm for ALTER TABLE in MySQL is COPY, which creates a new table, copies all rows, and rebuilds indexes. During this process, the table is locked with a write lock, blocking DML operations and causing increased write latency. In a Multi-AZ deployment, the DDL is replicated to the standby, but the lock on the primary delays writes, which can manifest as replication lag when the standby applies the same blocking DDL.

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 index creation DDL statement is not replicated to the standby instance, causing inconsistency.
Why it's wrong here
DDL statements are replicated; the issue is the lock on the primary.
✗
The instance size is insufficient for the write workload.
Why it's wrong here
The instance is db.r5.4xlarge, which is typically sufficient for 10K writes/sec; the issue appeared after index creation.
✓
The index was created using the default algorithm (COPY), which locks the table and blocks writes, causing replication lag.
Why this is correct
In MySQL 5.6 and 5.7, ALTER TABLE uses COPY algorithm by default, which locks the table for writes during the operation.
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 new index is causing excessive overhead on write operations due to index maintenance.
Why it's wrong here
Index maintenance adds some overhead but not typically enough to cause significant latency and lag; the problem is the creation process.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often assume any index addition causes permanent write overhead (Option D), but the question describes a sudden latency spike immediately after the operation, which is characteristic of the blocking COPY algorithm, not ongoing maintenance.

Detailed technical explanation

How to think about this question

In MySQL 8.0, the default ALGORITHM for ALTER TABLE is INPLACE for many operations, but for operations that require a full table rebuild (like adding an index to a large table without using ALGORITHM=INPLACE explicitly), MySQL falls back to COPY. The COPY algorithm acquires an exclusive metadata lock (MDL) and a table-level write lock, blocking all concurrent writes. In a Multi-AZ RDS setup, the DDL is applied on the primary first, then replicated; the standby must also execute the same blocking operation, which can cause replication lag if the copy takes significant time.

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

An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.

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.

Related DBS-C01 practice-question pages

Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.

Workload-Specific Database Design practice questions

Practise DBS-C01 questions linked to Workload-Specific Database Design.

Deployment and Migration practice questions

Practise DBS-C01 questions linked to Deployment and Migration.

Management and Operations practice questions

Practise DBS-C01 questions linked to Management and Operations.

Monitoring and Troubleshooting practice questions

Practise DBS-C01 questions linked to Monitoring and Troubleshooting.

Database Security practice questions

Practise DBS-C01 questions linked to Database Security.

DBS-C01 fundamentals practice questions

Practise DBS-C01 questions linked to DBS-C01 fundamentals.

DBS-C01 scenario practice questions

Practise DBS-C01 questions linked to DBS-C01 scenario.

DBS-C01 troubleshooting practice questions

Practise DBS-C01 questions linked to DBS-C01 troubleshooting.

Practice this exam

Start a free DBS-C01 practice session

Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.

10 questions 20 questions 30 questions 50 questions Timed 30

DBS-C01 practice-test guide →Study guide →Browse all practice tests

FAQ

Questions learners often ask

What does this DBS-C01 question test?

Workload-Specific Database Design — This question tests Workload-Specific Database Design — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The index was created using the default algorithm (COPY), which locks the table and blocks writes, causing replication lag. — Option C is correct because the default algorithm for ALTER TABLE in MySQL is COPY, which creates a new table, copies all rows, and rebuilds indexes. During this process, the table is locked with a write lock, blocking DML operations and causing increased write latency. In a Multi-AZ deployment, the DDL is replicated to the standby, but the lock on the primary delays writes, which can manifest as replication lag when the standby applies the same blocking DDL.

What should I do if I get this DBS-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.

About these practice questions

Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →

How Courseiva writes practice questions · Editorial policy

Keep practising

Question Discussion

Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.

Loading comments…

This DBS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DBS-C01 exam.