docs: add MySQL 8.4 migration guide for customers#10163
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Customer-facing guide covering how to enable MySQL 8.4 via pantheon.yml, pre-migration checklist, CMS compatibility matrix, reserved word conflicts, migration process and timing, common post-migration issues (ONLY_FULL_GROUP_BY, collation mismatches), and limitations. Refs: PRT-3742
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rachelwhitton
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stevector
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| - **No self-service rollback.** Reverting from MySQL 8.4 to MariaDB requires Pantheon support. Always test on a [Multidev](/guides/multidev) first. | ||
| - **Backups are engine-specific.** A backup taken on MySQL 8.4 cannot be restored to a MariaDB environment, and vice versa. | ||
| - **MariaDB 10.6 required.** Your site must be on MariaDB 10.6 before migrating to MySQL 8.4. Sites on older MariaDB versions will be upgraded to 10.6 first automatically. |
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@kanishkaverma in Slack we discussed making this a recommendation rather than a requirement. Let's hold off on publishing until we know for certain.
stevector
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stevector
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stevector
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| | WordPress 6.x | All versions | Fully compatible | | ||
| | WordPress 5.x | 5.9+ | Older versions may hit reserved word or sql_mode issues | | ||
| | Drupal 10 | 10.2+ | Earlier versions may need patches for the `GROUPS` reserved word | |
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What patches would they need? It might be wiser for us to just recommend upgrading to the highest available point release.
stevector
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stevector
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stevector
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stevector
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stevector
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stevector
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| Before enabling MySQL 8.4, consider the following limitations: | ||
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| - **No self-service rollback.** Reverting from MySQL 8.4 to MariaDB requires Pantheon support. Always test on a [Multidev](/guides/multidev) first. | ||
| - **Backups are engine-specific.** A backup taken on MySQL 8.4 cannot be restored to a MariaDB environment, and vice versa. |
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Why can't a backup taken in MariaDB be imported to a MySQL environment? aren't we doing this conversion with a backup and import?
stevector
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Jul 13, 2026
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| ## How to Enable MySQL 8.4 | ||
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| Add the following to your site's `pantheon.yml` file: |
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Before we merge this PR we need to figure out which upstreams have are getting their pantheon.upstream.yml changed on which dates
Co-authored-by: Steve Persch <stevector@users.noreply.github.com>
Co-authored-by: Steve Persch <stevector@users.noreply.github.com>
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Adds a new page to the MariaDB and MySQL guide covering MySQL 8.4 migration.
Content
Context
MySQL 8.4 LTS support is nearing GA. This guide is part of pre-release prep for PS/CS/TS readiness (PRT-3742). Based on at-scale validation of 14 sites from 0 MB to 85 GB (PRT-3727).
The pantheon.yml page will also need an update to mention MySQL 8.4 alongside MariaDB versions, but that can be a follow-up.
Refs: PRT-3742