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APC Object Cache Backend
APC User Cache Entries and WP Super Cache (3 posts)

  1. RavanH
    Member
    Posted 1 year ago #

    Hi,

    Running WP Super Cache with APC (php5-fpm) installed, I see APC cahce being used only for System Cache Entries. This is good.

    After installing APC Object Cache Backend, I see that User Cache Entries are now filling the the APC cache too. This is better. Or is it?

    They are causing about 100% fragmentation all the time and regular Cache full count hits (I'm on a low-end/limited memory VPS)... How bad is this for performance?

    And another thing I notice is that changing a setting like the Site Name on the Settings > General admin page, it looks like the change did not have an effect. Looking in the database the change did take place so clearly the old value came from the cache.

    Are the user cache entries not cleared during admin changes? And if it should be, would this be up to WP Super Cache or APC Object Cache Backend?

    Thanks :)

    http://wordpress.org/extend/plugins/apc/

  2. RavanH
    Member
    Posted 1 year ago #

    Ah... in object-cache.php I see:

    function flush() {
    		// Don't flush if multi-blog.
    		if ( function_exists( 'is_site_admin' ) || defined( 'CUSTOM_USER_TABLE' ) && defined( 'CUSTOM_USER_META_TABLE' ) )
    			return true;
    
    		return apc_clear_cache( 'user' );
    	}

    And yes, I'm on Multi-site... I suppose this is done to prevent the user cache from being cleared ALL the time on large multi-sites? Or is wp_cache_delete() used when updating admin settings and is something else going wrong?

  3. Donncha O Caoimh
    Member
    Posted 1 year ago #

    Super cache and APC are completely separate caching mechanisms. Supercache can use an external object cache but it's *very* experimental and only there if you want to hack on it.

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