Free PCDBE sample questions

Correct answers: Configure a continuous DMS migration job to keep the Cloud SQL target synchronized with the on-premises Oracle source.; Establish a reverse replication stream from the Cloud SQL target back to the on-premises Oracle source after the cutover.

A continuous migration job using Change Data Capture (CDC) is essential for minimizing downtime. It performs the initial bulk copy and then streams ongoing changes, allowing the target database to remain in sync with the source until the final cutover.

Setting up reverse replication is a critical part of a fallback plan. After promoting the Cloud SQL instance and directing traffic to it, this reverse stream sends any new changes back to the original source database. This keeps the source 'warm' and enables a rapid rollback to the on-premises environment if a critical issue is discovered in the new Google Cloud application.

Correct answer: Cloud Bigtable, with a row key of `userId#reversed_timestamp`. This design prevents hotspotting and keeps a user's events contiguous and sorted for efficient reads.

Cloud Bigtable is ideal for massive-scale, low-latency write workloads like this event ingestion scenario. The key to performance is the row key design. A `userId` prefix groups all events for a single user together. Appending a reversed timestamp (e.g., `Long.MAX_VALUE - timestamp`) ensures that the most recent events are stored at the beginning of the row range for that user. This makes the query for the 'last N events' a highly efficient scan of just a few rows, satisfying all requirements.

Correct answer: False

This statement is false. The purpose of the standby instance in a Cloud SQL HA configuration is solely for failover. It is a 'hot standby' that takes over if the primary instance becomes unavailable. It does not serve read traffic. To scale read throughput, you must create one or more separate read replicas.

Correct answer: Configure a cross-region read replica and have a documented procedure to manually promote it in case of a regional outage.

The standard HA configuration for Cloud SQL protects against zonal failures, not regional failures. To meet a low RTO for a regional disaster, you must have a replica in another region. A cross-region read replica serves this purpose. While replication is asynchronous (meaning RPO is not strictly zero, but very close), it is the standard and required Cloud SQL pattern for regional DR. The promotion must be handled manually or via automation scripts, as it's not an automatic process like zonal HA failover.

Correct answer: Create a composite index on the `(category, is_active)` columns of the `products` table.

The problem describes queries filtering by two specific columns, which are causing full table scans. This is a classic indicator of a missing index. A composite index on the columns used in the `WHERE` clause (`category` and `is_active`) will allow the database to directly look up the required rows instead of scanning the entire table, which is the most direct and efficient solution.

Correct answer: A composite index on the `inventory` array field and the `skill_level` field.

Firestore requires an index for every query it executes. A simple query on one field will use a default single-field index. However, this query involves a range filter (`skill_level > 90`) and an array membership filter (`inventory` contains `rare_item`). To perform this query efficiently, Firestore requires a manually created composite index that includes both fields. Without it, the query would be rejected by the Firestore API.

Correct answer: 1. Configure source connectivity. 2. Create and run a continuous migration job. 3. Monitor replication delay. 4. Stop the source application. 5. Promote the Cloud SQL replica. 6. Reconfigure the application to connect to Cloud SQL.

This sequence follows the Google-recommended best practices for a near-zero downtime migration with DMS. You first set up connectivity, then start the continuous job which handles the initial dump and ongoing replication. It's crucial to monitor the replication delay to ensure the target is caught up before cutover. The cutover itself involves stopping the application to prevent new writes to the old source, promoting the Cloud SQL instance to a standalone, writable server, and finally, pointing the application to the new database.

Correct answer: Provision a new read pool instance in the AlloyDB cluster and direct all analytical dashboard queries to the read pool's endpoint.

AlloyDB's architecture is designed for this exact scenario. A read pool provides one or more dedicated, compute-only nodes that can be scaled independently from the primary instance. They access the same shared storage layer, ensuring they are always up-to-date with minimal replication lag. By directing the analytical queries to the read pool's endpoint, you isolate their compute and memory usage from the primary instance, allowing both transactional and analytical workloads to perform optimally without interfering with each other.

Correct answer: Clone the instance immediately before the upgrade. If rollback is needed, delete the upgraded instance and rename the clone to take its place.

Cloning a Cloud SQL instance is a fast operation that creates a new, fully independent instance with a copy of the data from a specific point in time. This is the ideal approach for creating a pre-upgrade snapshot. The rollback process is also very fast: simply redirect the application's connection string to the clone's IP address. This avoids the lengthy data restore process and easily meets the 30-minute window.