replacing btree index with unique index for performance gains

[jakwinkler]

Description (*)

Replacing btree index with unique index for performance gains in catalog_product_entity_media_gallery_value table. Thanks to that we also assure data integrity.

Fixed Issues (if relevant)

1. Fixes Consider adding a unique key to catalog_product_entity_media_gallery_value #36190

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)

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[Copilot]

Pull Request Overview

This PR replaces a non-unique btree index on catalog_product_entity_media_gallery_value(entity_id, value_id, store_id) with a unique constraint to improve query performance and enforce data integrity.

• Changed an existing btree index to a unique constraint
• Renamed the index reference to include a _UNQ suffix
• Ensures duplicate rows on (entity_id, value_id, store_id) cannot be inserted

Comments suppressed due to low confidence (3)

app/code/Magento/Catalog/etc/db_schema.xml:887

• [nitpick] Add a brief XML comment above this line explaining why a unique constraint is used (performance benefits and data integrity) so future maintainers understand the change.

        <constraint referenceId="CAT_PRD_ENTT_MDA_GLR_VAL_ENTT_ID_VAL_ID_STORE_ID_UNQ" xsi:type="unique">

app/code/Magento/Catalog/etc/db_schema.xml:887

• Add an integration test to verify that inserting a duplicate (entity_id, value_id, store_id) row is rejected by this new unique constraint.

        <constraint referenceId="CAT_PRD_ENTT_MDA_GLR_VAL_ENTT_ID_VAL_ID_STORE_ID_UNQ" xsi:type="unique">

app/code/Magento/Catalog/etc/db_schema.xml:887

• Consider benchmarking insert/update operations on catalog_product_entity_media_gallery_value after this change to ensure write performance remains acceptable.

        <constraint referenceId="CAT_PRD_ENTT_MDA_GLR_VAL_ENTT_ID_VAL_ID_STORE_ID_UNQ" xsi:type="unique">

[ihor-sviziev]

@magento run all tests