WP_PJAX_PageCache::clearCache implemenation is bugos

[eimanavicius]

wp-pjax/inc/PageCache.php

Line 159 in b9f4abf

$wpdb->query( "DELETE FROM ". $wpdb->prefix ."options WHERE option_name LIKE ('_transient_".WP_PJAX_TRANIENT_PREFIX."%')" );

phpcs: WordPress.VIP.DirectDatabaseQuery: Usage of a direct database call is discouraged.

Deleting "transient%" options from database does not mean cache cleared. Other back-end can be used (ex. memcache, redis).
Cache versions can be used to invalidate cache. Version would be stored in cache and changed when clearing cache.

[pelmered]

Good point. The only way to do this must be to make a select query to get all the transient keys and then loop through them and then run delete_transient() on each one. Not very pretty, but that would allow any backend to handle this.

Or do you have any suggestions/ideas?

The page cache functionality nerver really worked very good, and should probably get a rewrite as well.

[eimanavicius]

Well selecting all key would not help as database is not the only possible cache back-end.

My suggestion would be:

Cache version can be used to invalidate cache. Version would be stored in cache and changed when clearing cache.

This technique is used in Doctrine 2 ORM caching solution.

[pelmered]

You mean something like generating keys like prefix_<version (generated random string)>_<key> and then generate a new version string when you clear the cache? For example: wp_pjax_pc-876b438o-test-page
That would be a good solution.

[eimanavicius]

Yes, exactly