Key takeaways
- Over time, WordPress databases fill with revisions, transients, spam, orphaned data and bloated autoloaded options.
- Cleaning up and limiting future bloat speeds up the admin and dynamic pages, and makes backups smaller.
- Always back up before cleaning, and be careful with tools that delete data automatically.
Page caching hides many database problems from visitors — but not from logged-in users, WooCommerce customers, search, or the admin. If your dashboard feels slow or your backups keep growing, the database is a good place to look.
What bloats a WordPress database#
| Item | Where | Typical fix |
|---|---|---|
| Post revisions | wp_posts |
Limit and clean old revisions |
| Auto-drafts and trashed posts | wp_posts |
Empty trash; delete old auto-drafts |
| Spam and trashed comments | wp_comments |
Delete |
| Expired transients | wp_options |
Delete expired transients |
| Large autoloaded options | wp_options |
Find and fix plugins storing huge autoloaded data |
| Leftover tables from deleted plugins | Custom tables | Remove carefully after confirming they’re unused |
| Orphaned post meta | wp_postmeta |
Clean with a tool |
| Logs (security, email, 404) | Plugin tables | Set retention limits |
Step-by-step cleanup#
- Back up the database — see backup guide.
- Measure: check table sizes in phpMyAdmin or with
wp db size --tables. - Clean safely with a plugin like WP-Optimize or Advanced Database Cleaner (or WP-CLI:
wp transient delete --expired,wp post delete $(wp post list --post_type=revision --format=ids)). - Check autoload: Tools → Site Health warns when autoloaded options are too large; inspect the biggest with:
SELECT option_name, LENGTH(option_value) AS size FROM wp_options WHERE autoload IN ('yes','on') ORDER BY size DESC LIMIT 20; - Optimise tables (InnoDB generally manages this well; run OPTIMIZE only occasionally).
- Test the site, forms and checkout.
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Prevent bloat#
// wp-config.php
define( 'WP_POST_REVISIONS', 10 );
define( 'EMPTY_TRASH_DAYS', 14 );
define( 'AUTOSAVE_INTERVAL', 120 );- Set log retention in security, redirect and email-log plugins.
- Delete plugins properly (some offer “remove data on uninstall”).
- Use object caching (Redis) on dynamic sites to reduce repeated queries.
- For WooCommerce, enable High-Performance Order Storage when compatible.
Find slow queries#
Install Query Monitor temporarily: it lists slow and duplicate database queries per page and which plugin triggered them. Often a single plugin causes most of the load.
Database optimization FAQ#
Will cleaning the database speed up my site?#
It helps dynamic and admin pages, especially with large autoloaded options. Cached front-end pages see less difference.
How often should I clean it?#
Monthly or quarterly for most sites, plus limits that prevent bloat.
Is it safe to delete all revisions?#
Yes, technically, but keeping a few recent revisions per post is useful for undoing mistakes.