XTDB, which is mentioned in the post, is subtly different from the other Clojure-based Datalog systems in this respect, because its Datalog engine executes in terms of multi-way joins using a "Worst-Case Optimal Join" implementation that is ideal for graph processing (vs. a tree of binary hash joins). Therefore, based on statistics and query planning heuristics, it will often perform graph pattern matching before resolving the logic/horn clauses. (source: I work on the XTDB team)
Interesting architecture:
https://raw.githubusercontent.com/xtdb/xtdb/master/docs/conc...
Btw, is that 'RocksDB or ?' for the local store current or other storage engines can get plugged in?
p.s. this is datomic's architecture for comparison.
Hmm, it seems there's some SVG rendering issue when viewing directly. It should say "LMDB" in that empty spot. It renders okay for me on the GitHub readme: https://github.com/xtdb/xtdb (and here https://docs.xtdb.com/concepts/what-is-xtdb/)