Hi organicAnt. I’m surprised Matt didn’t mention this already, but yes, looking at Piwik in your browser can indeed cause some major backend processing like you’re seeing, and yes, there are settings to work with this.
There are two ways that Piwik can summarize and generate reports. The first is when you browse the Piwik interface, it can generate the reports on as you do so:
Pro: The reports are 100% accurate with no delay.
Con: The reports must generate when you reload the page, go forward and backward, etc.
Con: Reports can take a lot of processing to generate.
Con: Your browsing can be significantly slower, depending on your traffic.
The second way that Piwik can summarize and generate reports is via an “archive script” that you set up as a cron job.
Con: Less accurate when browsing due to the delay of the cron job.
Pro: Less processing overall – reports are generated only as often as configured
Pro: Faster browsing
There’s an FAQ that describes how to set this up.
You might also want to check out the FAQ on tweaking MySQL: