[brendanyounger]

I greatly respect what Stu and Rich have done to make Datomic.

However, they made an explicit design decision to not include a query optimizer and execute the clauses as they were written. This is usually fine since the author has some idea of what the best order is, but there are O(2^k) different permutations of clauses so doing it by hand will fail at some point (if you want the optimal ordering).

[refset]

I asked Rich about his thoughts on query optimizers last year (not in the context of Datomic specifically) and his only reservation was around the practical implications for the operational experience. Specifically, that database systems should always provide the means for developers to control exactly how/when/whether existing (cached) execution plans get re-optimized, otherwise query optimizers can actually be a source of greater problems than they solve, particularly for applications with extremely rapid changes in data.