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Certain WordPress UI functions were slowing down my app (igrealty.com). It seems whenever I upload images, save and delete posts or delete assets from the media library the app spikes in slowness. New Relic produces alerts and things go very slowly. Here's a grab: http://imgur.com/NzyG6
Disabling all my plugins and reactivating one by one I found that WordPress Varnish is the culprit. With WordPress Varnish disabled my app is much faster with more normal page load times. Apdex > .7.
Anyone else having this problem?
I suspect that you have an issue with the server IP or Port configuration in the admin, or, for some reason the Varnish server you're talking to has your Webserver IP firewalled.
If you can make sure that the IP address and port are correct and see if the problem persists, I would suspect that the connection is firewalled. Since it is firewalled, each purge attempt would take 27 seconds to time out, and, if you were updating things that required multiple purges, that would slow down the administration console.
Another possibility is that you are not running the vcl from the plugin. If the PURGE option isn't enabled in the Varnish VCL, it'll pass the request through to Apache which will get a 404, which is not cached and would cause WordPress to generate the 404 page.
I realize this is an old ticket, but, I've gone through things on multiple machines to debug this and I did run into the slowness when I didn't have the VCL enabled.