Visits per Server Time wrong for most, but not all days

I’ve just become aware of the fact that almost all the Visits per Server Time reports I view are offset by -3 hours. Oddly, if I use today or yesterday as my date range, then the reported activity for any given hour is correct. Apart from knowing the general usage pattern of my site, I also am checking with Google Analytics and an old in-house tracking tool to confirm that these Piwik reports are wrong.

My server timezone is UTC, and my site is configured in Piwik to Eastern Time (-5 New York).

A couple of days ago I did experiment with changing the site’s timezone, trying several different ones from across the globe, just to see how it affects the reports and the API results. I was sure to reset everything back to the proper settings when I was done. I am wondering if doing that may have somehow adversely effected Piwik’s data. It’s a long-shot, but I just can seem to figure this out.

Has anyone else ever experienced any problem similar to this?

When you change the timezone it will then use the TZ to process reports. Report processed while you were experiencimenting will be slightly off. You can re-process all data if you want but can take a while (see the faq to reprocess all data)

Thanks Matt, that solved my immediate problem… I must’ve had the wrong timezone configured since day one up until my tests… that would explain the majority of my history being off.

It seems unfortunate that it has to work like this, as it sounds like any timezone change will make all your historical data off by x number of hours, which I assume also affects individual day/week/month totals as well. In a situation where an instance of Piwik has multiple sites configured, is it possible to reprocess the logs of a single site rather than nuking an entire time period for all sites, or is it only the absence of the entire archive table itself the trigger to regenerate that data?

all data analysis tool work like this, for performance reasons