It is exactly the same for all sites
Hi Fabian Becker, since I do not have command line access I have done a web based run “http://stats.mydomain.com/misc/cron/archive.php?token_auth=XYZ”. It has done it’s job without reporting any error. I just reports successfully done to all with nothing skipped. However nothing changes. Cheers
Edit 1: I just had a look at the database itself. Yeah, the piwiki_log_visit table is at 4.8 MiB. This means that the web based cron run does not work for me. No other solution availabe. 
I just wonder why I get not error reports and instead just done to all.
Edit 2: Just attached the report. Cheers
If piwik is not tracking any data, there is a problem not related to the memory, but to Tracking. Enable debug as per: http://piwik.org/docs/tracking-api/reference/#toc-debugging-the-tracking-api-requests and you should see an error message. Also check your server error logs.
Just to sum up:
After I enabled web cron for the site the archiving works ok from that day (Dec. 2) onwards and the graphs etc. are now shown. - This is cool.
However, there seems to be no way to process the 4.8 MiB of data collected for November since I do not have shell access and only 128 MB of memory, meaning that I indeed have the tracked data available but no means to process them. - This is not so cool.
Would it be a valid feature request to have some means to do a selective processing for distinct spans of time instead of the time since last login?
I am sorry for coming back to this that late.
I just tried to solve the problem with the solution you directed me to. However it does not work. I guess the reason for this is that the scipt again fails to do this for the very reason it did not create them properly in the first place: Just to much data for the given memory. I just get back empty new tables. So to sum up: There seems to be no way to process the 5 MB of log data which are still stitting there.
Marbot
After a unsatisfactory attempt with Arvixe who’s support is not existant I moved my Piwik Hosting to
Thomas Seifert
Web: http://www.mysnip-solutions.de
E-Mail: thomas.seifert@mysnip.de
and everything is running smoothly.
When it comes to Piwik this guy seems to know what he’s doing and provides a fully managed service.
Actually I am not at Arvixe and I will not even blame this on Piwik. The root of the problem is that I did not set up Piwik properly in the first place (cron/webcrom) and was all of a sudden run over by an “armada” of visitors.
Just another idea struck my mind: I will try to process data on my pc and then import them to this database. Keeping fingers crossed.