Query performance with rules is much worse than "equivalent" inline clause

[RutledgePaulV]

I was attempting to clean up a few queries by factoring out some simple rules from my :where clauses. However, I immediately began noticing a big decrease in query performance and increased memory usage. I was able to simplify it down to a pretty simple example.

I reproduced the issue on both 1.4.2 and 1.5.4 so I don't think it's a recent regression.

(require '[datascript.core :as d])

(def db
    (-> (d/empty-db)
        (d/db-with (for [x    (range 50000)
                         :let [temp (str (random-uuid))]
                         fact [[:db/add temp :item/id x]
                               [:db/add temp :item/status (rand-nth ["started" "pending" "stopped"])]]]
                     fact))))

; inline clauses, this is fast / performs as expected
(time
    (def results
      (d/q '[:find ?e
             :where
             [?e :item/status ?status]
             [(ground "pending") ?status]]
           db)))

; "Elapsed time: 13.563333 msecs"

; logically equivalent rule, but much slower and sometimes exceeds my default max heap!
(time
    (def results
      (d/q '[:find ?e
             :in $ %
             :where
             [?e :item/status ?status]
             (pending? ?status)]
           db
           '[[(pending? ?status)
              [(ground "pending") ?status]]])))

; "Elapsed time: 53745.881542 msecs"

[RutledgePaulV]

Proposed fix: https://github.com/tonsky/datascript/pull/457

[RutledgePaulV]

Same test from initial report after the change:

(def db
  (-> (d/empty-db)
      (d/db-with (for [x    (range 50000)
                       :let [temp (str (random-uuid))]
                       fact [[:db/add temp :item/id x]
                             [:db/add temp :item/status (rand-nth ["started" "pending" "stopped"])]]]
                   fact))))

(time
  (def results
    (d/q '[:find ?e
           :where
           [?e :item/status ?status]
           [(ground "pending") ?status]]
         db)))

; "Elapsed time: 11.420875 msecs"

(time
  (def results
    (d/q '[:find ?e
           :in $ %
           :where
           [?e :item/status ?status]
           (pending? ?status)]
         db
         '[[(pending? ?status)
            [(ground "pending") ?status]]])))

; "Elapsed time: 16.736916 msecs"

[tonsky]

Closed in #457