Improved performance of post previews

[jloh]

ref https://linear.app/ghost/issue/ENG-2081

• Added an index to the posts table on the uuid column to prevent a whole table scan when doing a posts preview which use a posts UUID to match against
• On sites with a large number of posts this can currently cause lookups to take several seconds just to look up a single post

Cost before index:

| -> Limit: 1 row(s)  (cost=68964 rows=1) (actual time=333..333 rows=1 loops=1)
    -> Filter: (posts.uuid = '5e75e7da-bdcc-4a5c-ac7f-876041f4aa1d')  (cost=68964 rows=8127) (actual time=333..333 rows=1 loops=1)
        -> Table scan on posts  (cost=68964 rows=81271) (actual time=0.0641..325 rows=78701 loops=1)

Cost after index:

| -> Limit: 1 row(s)  (cost=0.63 rows=1) (actual time=0.0717..0.0718 rows=1 loops=1)
    -> Index lookup on posts using posts_uuid_test_index (uuid='5e75e7da-bdcc-4a5c-ac7f-876041f4aa1d')  (cost=0.63 rows=1) (actual time=0.0707..0.0707 rows=1 loops=1)

Adding the index on a site with 140k+ posts took ~1.4 seconds:

> ALTER TABLE `posts` ADD INDEX `posts_uuid_test_index`(`uuid`);
Query OK, 0 rows affected (1.44 sec)
Records: 0  Duplicates: 0  Warnings: 0

[coderabbitai]

Walkthrough

A new migration file has been created to add an index to the uuid column of the posts table in the database. This file imports a utility function, createAddIndexMigration, and uses it to define the migration. The migration is exported as a module, indicating the target table (posts) and the column (uuid) for the index addition. Additionally, the uuid field's schema definition has been updated to include an index property, while retaining its original properties. Furthermore, the currentSchemaHash constant in the database integrity test has been updated to reflect the changes in the schema.

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[github-actions]

It looks like this PR contains a migration 👀
Here's the checklist for reviewing migrations:

General requirements

• ⚠️ Tested on the staging database servers
• Satisfies idempotency requirement (both up() and down())
• Does not reference models
• Filename is in the correct format (and correctly ordered)
• Targets the next minor version
• All code paths have appropriate log messages
• Uses the correct utils
• Contains a minimal changeset
• Does not mix DDL/DML operations
• Tested in MySQL and SQLite

Schema changes

• Both schema change and related migration have been implemented
• For index changes: has been performance tested for large tables
• For new tables/columns: fields use the appropriate predefined field lengths
• For new tables/columns: field names follow the appropriate conventions
• Does not drop a non-alpha table outside of a major version

Data changes

• Mass updates/inserts are batched appropriately
• Does not loop over large tables/datasets
• Defends against missing or invalid data
• For settings updates: follows the appropriate guidelines

[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (1)

ghost/core/core/server/data/schema/schema.js (1)

53-53: Excellent performance optimization by adding index to posts.uuid

Adding an index to the UUID column is a well-considered optimization that will significantly improve query performance when looking up posts by UUID. According to the PR description, this change reduced lookup costs from 68964 rows to 0.63 rows and decreased lookup time from ~333ms to ~0.0718ms.

This change directly addresses the performance issues with post previews on sites with large post collections, where lookups were previously taking several seconds due to full table scans.

Consider reviewing other frequently queried columns in the system for potential indexing opportunities, especially for tables that grow large over time.

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📥 Commits

Reviewing files that changed from the base of the PR and between ce75740869af204000e5a55cd59a515e0026c81d and 5d385ba.

📒 Files selected for processing (3)

• ghost/core/core/server/data/migrations/versions/5.114/2025-03-19-03-13-04-add-index-to-posts-uuid.js (1 hunks)
• ghost/core/core/server/data/schema/schema.js (1 hunks)
• ghost/core/test/unit/server/data/schema/integrity.test.js (1 hunks)

🚧 Files skipped from review as they are similar to previous changes (1)

• ghost/core/core/server/data/migrations/versions/5.114/2025-03-19-03-13-04-add-index-to-posts-uuid.js

⏰ Context from checks skipped due to timeout of 90000ms (8)

• GitHub Check: Ghost-CLI tests
• GitHub Check: Database tests (Node 20.11.1, sqlite3)
• GitHub Check: Database tests (Node 22.13.1, mysql8)
• GitHub Check: Regression tests (Node 20.11.1, mysql8)
• GitHub Check: Database tests (Node 20.11.1, mysql8)
• GitHub Check: Database tests (Node 18.12.1, mysql8)
• GitHub Check: Unit tests (Node 20.11.1)
• GitHub Check: Unit tests (Node 18.12.1)

🔇 Additional comments (1)

ghost/core/test/unit/server/data/schema/integrity.test.js (1)

38-38: Schema hash updated to reflect database changes

This update to the hash value is required due to the addition of an index to the 'uuid' column in the 'posts' table. The hash value ensures that any changes to the database schema are properly tracked and validated.