Permissions & Access Control Issues

SPARQL SELECT COUNT(*) queries are slow

Counting is inherently slow. Even more so when you need to read the stuff you
count from disk. If you need faster disk access I recommend using more
disks and spread them on different SATA buses (if you've SATA disk) and
tell Virtuoso to use stripes. This way you'll have more Disk I/O
bandwidth and parallelization.