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Protect datalog cache from early cancellation #657

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merged 6 commits into from
Jan 2, 2025
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dwwoelfel
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This prevents in-progress datalog queries from getting cancelled when there are multiple sessions waiting on the query.

Previously, we could get into a situation like this:

  1. user-1 opens a session and runs query-a
  2. user-2 opens a session and runs query-a
  3. user-1 closes their session
  4. we cancel all in-progress queries, including query-a
  5. user-2 gets an error for query-a because the query was cancelled

This PR moves the query execution to a separate call stack where it won't get canceled if the parent is canceled.

To keep the behavior where we cancel queries that exceed the handle-receive-timeout-ms, we add another future that is in the call stack. If it gets canceled and there are no other threads waiting on the query, then it will cancel the query.

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View Vercel preview at instant-www-js-dont-cancel-jsv.vercel.app.

@@ -342,23 +347,112 @@
;; ------
;; datalog cache

(defn swap-datalog-cache-delay! [conn app-id datalog-query delayed-call]
(defn swap-datalog-cache! [conn app-id datalog-query-fn ctx datalog-query]
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🤯 I salute you sir.

;; We added it, so we must execute it
(let [stmt-tracker (sql/make-top-level-statement-tracker)
result-promise (:promise @result-delay)
work-fut (binding [ua/*child-vfutures* nil ;; Move future to a new "call-stack"
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Man, bind + statement-tracker makes for a really powerful abstraction.

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@stopachka stopachka left a comment

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Beautiful work @dwwoelfel !

@dwwoelfel dwwoelfel changed the title [in-progress] Protect datalog cache from early cancellation Protect datalog cache from early cancellation Jan 2, 2025
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So darn cool!

@dwwoelfel dwwoelfel merged commit 6f24813 into main Jan 2, 2025
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@dwwoelfel dwwoelfel deleted the dont-cancel branch January 2, 2025 21:44
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2 participants