I know its a very vague description but the symptoms are these:
if I enable the plugin, even if I have disabled caching, my server load goes up like crazy, even if I am the only one currently browsing my site.
As soon as I disable the plugin everything is back to normal.
BUT it was running perfectly smooths just a couple of days ago.
What happened in-between?
As far as I can remember, I updated Debian with the latest patches, I updated W3 Total Cache, I added a new custom post type to my site and made some cosmetical changes. Nothing that could trigger this. Btw. caching to memcached.
Any idea what to check or how to trace this? It was more or less luck that I deactivated this plugin and saw that the load went down. It might not even be the plugin but an incompatibility of it with something else?