Quick Answer
The answer is to use INFORMATION_SCHEMA.INNODB_TRX to identify blocking queries causing table locks in Cloud SQL for MySQL. This view exposes real-time transaction metadata, including the transaction ID, state, and a waiting flag, which when joined with INNODB_LOCK_WAITS and INNODB_LOCKS reveals exactly which transaction is holding a lock and which is blocked. On the Google Professional Cloud Database Engineer exam, this tests your ability to diagnose InnoDB contention without relying on external tools—a common trap is reaching for SHOW PROCESSLIST, which only shows current queries, not lock dependencies. The key insight is that INNODB_TRX shows the blocker, not just the blocked. For a quick memory anchor, think “TRX for the blocker, WAITS for the victim.”
This PCDE practice question tests your understanding of monitor and optimize database performance. 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 Cloud SQL for MySQL database has frequent table locks causing contention and slow queries. Which diagnostic approach helps identify the blocking queries?
Set up a Cloud Monitoring alert on CPU
Why wrong: CPU alert may indicate contention but does not identify specific blocking queries.
Use Query Insights
Why wrong: Query Insights in Cloud SQL MySQL does not provide lock wait details.
Enable slow query log
Why wrong: Slow query log shows slow queries but not which query holds locks.
Use INFORMATION_SCHEMA.INNODB_TRX
This table shows transaction details including lock waits and blockers.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Use INFORMATION_SCHEMA.INNODB_TRX
Option D is correct because `INFORMATION_SCHEMA.INNODB_TRX` provides real-time data on all currently executing InnoDB transactions, including transaction IDs, state, and the waiting flag. By joining this with `INNODB_LOCK_WAITS` and `INNODB_LOCKS`, you can pinpoint which transaction is blocking others, directly addressing table lock contention in Cloud SQL for MySQL.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Set up a Cloud Monitoring alert on CPU
Why it's wrong here
CPU alert may indicate contention but does not identify specific blocking queries.
Use Query Insights
Why it's wrong here
Query Insights in Cloud SQL MySQL does not provide lock wait details.
Enable slow query log
Why it's wrong here
Slow query log shows slow queries but not which query holds locks.
Use INFORMATION_SCHEMA.INNODB_TRX
Why this is correct
This table shows transaction details including lock waits and blockers.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates confuse performance monitoring tools (Query Insights, slow query log) with transaction-level diagnostics, failing to recognize that only InnoDB metadata tables expose the blocking transaction chain.
Trap categories for this question
Command / output trap
Slow query log shows slow queries but not which query holds locks.
Detailed technical explanation
Under the hood, InnoDB uses a lock system where each transaction holds locks on rows or tables; `INFORMATION_SCHEMA.INNODB_TRX` shows the `trx_mysql_thread_id` and `trx_state`, while `INNODB_LOCK_WAITS` links the blocking and waiting transaction IDs. In a real-world scenario, a long-running `UPDATE` without an index can lock thousands of rows, and joining these tables reveals the exact `PROCESSLIST_ID` to kill the blocking session. A subtle behavior is that `INNODB_TRX` only shows active transactions, so short-lived locks may not appear if queried infrequently.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Monitor and optimize database performance — This question tests Monitor and optimize database performance — Read the scenario before looking for a memorised answer..
The correct answer is: Use INFORMATION_SCHEMA.INNODB_TRX — Option D is correct because `INFORMATION_SCHEMA.INNODB_TRX` provides real-time data on all currently executing InnoDB transactions, including transaction IDs, state, and the waiting flag. By joining this with `INNODB_LOCK_WAITS` and `INNODB_LOCKS`, you can pinpoint which transaction is blocking others, directly addressing table lock contention in Cloud SQL for MySQL.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This PCDE practice question is part of Courseiva's free Google Cloud 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 PCDE exam.
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