Craft occasionally runs a few garbage collection routines to remove stale data, including:

• Purge unsaved drafts (per the config:purgeUnsavedDraftsDuration config setting).
• Delete expired template caches.
• Purge any expired pending user accounts (per the config:purgePendingUsersDuration config setting).
• Hard delete expired soft-deleted rows (per the config:softDeleteDuration config setting).
• Delete stale user session data.
• Delete orphaned search indexes (any indexes belonging to elements that don’t exist anymore).

By default, each web request has a 1 in 100,000 chance of triggering garbage collection. That can be configured from config/app.php by overriding api:craft\services\Gc::$probability.

return [
    'components' => [
        'gc' => [
            'probability' => 0,     // no chance
            'probability' => 1,     // 1 in 1,000,000
            'probability' => 10,    // 1 in 100,000 (default)
            'probability' => 100,   // 1 in 10,000
            'probability' => 1000,  // 1 in 1,000
            'probability' => 10000, // 1 in 100
        ],
    ],
];

You can force garbage collection to run at any time with a terminal command.

In your terminal, go to your Craft project and then run:

./craft gc

If the shell is interactive, you will be asked whether Craft should delete all trashed items. If you enter yes at that prompt, all of your database rows that have been soft-deleted will get hard-deleted immediately, even if they hadn’t waited the full soft delete duration yet.

You can also force hard-deletion for all soft-deleted rows with the delete-all-trashed option:

./craft gc --delete-all-trashed=1