Added an index on automated_email_recipients.mailgun_message_id

[EvanHahn]

closes https://linear.app/ghost/issue/NY-1464
closes https://linear.app/ghost/issue/NY-1476

What

Adds an index to improve performance.

Along the way, had to add support for index prefixes in isMySQL.

Why

MySQL can't index long VARCHARs in full. You can solve this by hashing the value or by using an index prefix, which effectively only indexes the first N characters.

We chose the latter: an index prefix. We don't need uniqueness so it's okay if there's a little overlap.

The bulk of this PR adds support for those index prefixes, with the actual migration as a little sprinkle on top.

Test plan

Added several automated tests.

Also manually ran this SQL and checked the output, on both a fresh database and a migrated one:

SELECT * FROM information_schema.STATISTICS
WHERE table_name = 'automated_email_recipients'
AND column_name = 'mailgun_message_id';

I did not test this with real data on staging because (1) I didn't want to (2) I think it's relatively low-risk. Happy to do that if you think I should.

[github-actions]

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

General requirements

• ⚠️ Tested performance on staging database servers, as performance on local machines is not comparable to a production environment
• 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]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

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Review profile: CHILL

Plan: Pro

Run ID: 9e3824a1-43cb-4289-85c9-07aa851b925b

📥 Commits

Reviewing files that changed from the base of the PR and between 50274f6 and 79dd6a6.

📒 Files selected for processing (2)

• ghost/core/core/server/data/migrations/utils/schema.js
• ghost/core/core/server/data/migrations/versions/6.54/2026-07-21-21-08-15-add-automated-email-recipients-mailgun-message-id-index.js

---

Walkthrough

Adds MySQL prefix-index support to schema commands, including generated index names and configurable column-prefix lengths. Configures a 31-character index for automated_email_recipients.mailgun_message_id and adds a reversible migration. Updates schema seeding and integrity expectations, with unit tests covering index-name generation across SQLite and MySQL.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and accurately summarizes the main change: adding an index on automated_email_recipients.mailgun_message_id.
Description check	✅ Passed	The description is directly related to the changeset and accurately explains the index addition and MySQL prefix support.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch prefix-index-mailgun-id

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[nx-cloud]

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---

☁️ Nx Cloud last updated this comment at 2026-07-22 20:08:38 UTC

[codecov]

Codecov Report

❌ Patch coverage is 68.42105% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.80%. Comparing base (35e8331) to head (79dd6a6).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
ghost/core/core/server/data/schema/commands.js	70.27%	10 Missing and 1 partial ⚠️
.../core/server/data/schema/lib/default-index-name.js	65.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #29539      +/-   ##
==========================================
+ Coverage   74.53%   74.80%   +0.27%     
==========================================
  Files        1609     1611       +2     
  Lines      141475   141659     +184     
  Branches    17261    17320      +59     
==========================================
+ Hits       105443   105975     +532     
+ Misses      34998    34612     -386     
- Partials     1034     1072      +38     

Flag	Coverage Δ
e2e-tests	76.90% <68.42%> (+0.30%)	⬆️

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