✨ Reduce contention on file-update using advisory locks and weaker row locking.

backend/src/app/db.clj

@@ -11,6 +11,7 @@
    [app.common.geom.point :as gpt]
    [app.common.spec :as us]
    [app.common.transit :as t]
+   [app.common.uuid :as uuid]
    [app.db.sql :as sql]
    [app.metrics :as mtx]
    [app.util.json :as json]
@@ -366,3 +367,25 @@
 (defn pgarray->vector
   [v]
   (vec (.getArray ^PgArray v)))
+
+
+;; --- Locks
+
+(defn- xact-check-param
+  [n]
+  (cond
+    (uuid? n) (uuid/get-word-high n)
+    (int? n)  n
+    :else (throw (IllegalArgumentException. "uuid or number allowed"))))
+
+(defn xact-lock!
+  [conn n]
+  (let [n (xact-check-param n)]
+    (exec-one! conn ["select pg_advisory_xact_lock(?::bigint) as lock" n])
+    true))
+
+(defn xact-try-lock!
+  [conn n]
+  (let [n   (xact-check-param n)
+        row (exec-one! conn ["select pg_try_advisory_xact_lock(?::bigint) as lock" n])]
+    (:lock row)))

backend/src/app/db/sql.clj

@@ -43,8 +43,8 @@
   ([table where-params opts]
    (let [opts (merge default-opts opts)
          opts (cond-> opts
-                (:for-update opts)
-                (assoc :suffix "FOR UPDATE"))]
+                (:for-update opts)    (assoc :suffix "FOR UPDATE")
+                (:for-key-share opts) (assoc :suffix "FOR KEY SHARE"))]
      (sql/for-query table where-params opts))))
 
 (defn update

backend/src/app/rpc/mutations/files.clj

@@ -268,8 +268,9 @@
 (sv/defmethod ::update-file
   [{:keys [pool] :as cfg} {:keys [id profile-id] :as params}]
   (db/with-atomic [conn pool]
-    (let [{:keys [id] :as file} (db/get-by-id conn :file id {:for-update true})]
+    (let [{:keys [id] :as file} (db/get-by-id conn :file id {:for-key-share true})]
       (files/check-edition-permissions! conn profile-id id)
+      (db/xact-lock! conn id)
       (update-file (assoc cfg :conn  conn)
                    (assoc params :file file)))))