I didn’t make any specific test set, I just observed operation. But actually when I encountered that other thread it made me think about that dblock size thread, it could have been related to it. Therefore it’s like ly that I had changed dblock size (quite a while before the auto compact triggered) and then I just observed the results of it, much later. Making me wonder, why all of the files of the backup set have been rewritten.
As stated I’ve got three digit number of different backup sets, and after observing those, it seems that the most of the old blocks are still left after several compaction rounds, which is exactly the expected result and negates the “full auto compact” issue I were describing.
Actually I checked around 20 several months old daily backup storage sets to confirm this. Large blob of old files, then a few medium files tracking changes and additions to the original data set, and then the “revolving set” of fresh and small files. → Works just as intended afaik.
Yes, this is exactly the reason why I’m looking for option to limit / run partial compaction.