Manage a solution that can span multiple database technologies →mediumMultiple ChoiceObjective-mapped
PCDE Practice Question: Manage a solution that can span multiple database technologies
An application uses Cloud Firestore. The team notices that queries on a collection with an array field are slow. They want to create an index on the array field. What should they do?
⚠ Common exam trap
Google Cloud often tests the misconception that array fields cannot be included in composite indexes without special handling, but Firestore supports composite indexes containing array fields by default.
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
✓
Create a composite index on the array field and another field.
Cloud Firestore does not support single-field indexes on array fields. To enable efficient queries involving array fields, you must create a composite index that includes the array field along with another field. This allows Firestore to use the composite index for array-contains queries and other array operations, improving query performance.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Create a collection group index on the field.
Why it's wrong here
Collection group indexes are for queries across subcollections.
- ✓
Create a composite index on the array field and another field.
Why this is correct
Correct. A composite index that includes the array field is required to support array queries efficiently. This index enables the use of array-contains and other array-related operations.
- ✗
Create an index exemption for the array field.
Why it's wrong here
Incorrect. Index exemptions are used to exclude certain fields from automatic indexing, not to enable indexing on arrays. For array fields, you need an explicit composite index.
- ✗
Rely on the automatically created single-field index.
Why it's wrong here
Automatic index does not support array queries.
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