I’m gonna respawn this old thread since I had the same question and the documentation I’ve found wasn’t clear. I’ve found some answers and since google bring lot of people here I’ll share what I’ve found.
First of all: recorder save all the data from any sensor and any change is recorded. Recorder will purge old data after some days (default to 10) and you can include or exclude some sensor from recording to help reduce the size, that can become huge. Recorder data can be seen in history graphs and this are NOT statistics.
Only sensors that complies with long-term statistic are also packed by a totally different module. These data are NOT viewable from the history graphs, but from statistics graphs. When recoreder purges data, statistics are not affected. Statistics are like diamonds, they’re forever.
After all, only sensors configured to comply with statistics are tracked, and sensor tracked will just add a few bytes every day (24 hourly measures with max, min, mean value). Hence nothing to be worried about in decades.