Hi, I'm observing disk I/O when evaluating some queries which I am unable to explain. I have two datasets, one relatively small with the BATs taking up 1.6 MB on disk and one fairly large with 283 MB on disk. According to iostat, when I evaluate the attached query on the small dataset, 100 MB are written to disk, but none are read. This is on a Linux machine with 4 GB RAM running the Aug2011-SP3 release. I don't understand why data is written on disk, that (a) is never read again and (b) would easily fit into main memory. I am unable to evaluate the queries on the large dataset because MonetDB writes so much data that the disk fills up after a few minutes (more than 22GB). Please let me know if I can provide more information. Cheers, Viktor