Clear the task identifier cache when a lookup fails

.changeset/kind-otters-task-cache.md

@@ -0,0 +1,6 @@
+---
+"graphile-worker": patch
+---
+
+Clear the task identifier cache when a lookup fails, so a later poll retries
+instead of reusing the rejected promise (#638).

__tests__/taskIdentifiers.test.ts

@@ -0,0 +1,37 @@
+import type { EnhancedWithPgClient, TaskList } from "../src/interfaces.ts";
+import type { CompiledSharedOptions } from "../src/lib.ts";
+import { getTaskDetails } from "../src/taskIdentifiers.ts";
+
+const tasks: TaskList = {
+  send_email: () => undefined,
+};
+
+test("retries a task identifier lookup after the cached lookup rejects", async () => {
+  let attempts = 0;
+  const withPgClient = Object.assign(async () => undefined, {
+    withRetries: async () => {
+      attempts += 1;
+      if (attempts === 1) {
+        const error = new Error("admin shutdown");
+        Object.assign(error, { code: "57P01" });
+        throw error;
+      }
+      return { rows: [{ id: 7, identifier: "send_email" }] };
+    },
+  }) as EnhancedWithPgClient;
+  const compiled = {
+    escapedWorkerSchema: "graphile_worker",
+  } as CompiledSharedOptions;
+
+  await expect(getTaskDetails(compiled, withPgClient, tasks)).rejects.toThrow(
+    "admin shutdown",
+  );
+
+  const details = await getTaskDetails(compiled, withPgClient, tasks);
+  expect(attempts).toBe(2);
+  expect(details.taskIds).toEqual([7]);
+  expect(details.supportedTaskIdentifierByTaskId[7]).toBe("send_email");
+
+  await getTaskDetails(compiled, withPgClient, tasks);
+  expect(attempts).toBe(2);
+});

src/taskIdentifiers.ts

@@ -40,7 +40,7 @@ export function getTaskDetails(
     const { escapedWorkerSchema } = compiledSharedOptions;
     assert.ok(supportedTaskNames.length, "No runnable tasks!");
     cache.lastStr = str;
-    cache.lastDigest = (async () => {
+    const digestPromise = (async () => {
       const { rows } = await withPgClient.withRetries(async (client) => {
         await client.query({
           text: `insert into ${escapedWorkerSchema}._private_tasks as tasks (identifier) select i from unnest($1::text[]) as u(i) where not exists (select 1 from ${escapedWorkerSchema}._private_tasks as existing where existing.identifier = u.i) on conflict do nothing`,
@@ -69,6 +69,12 @@ export function getTaskDetails(
       cache.lastStr = str;
       return cache.lastDigest;
     })();
+    cache.lastDigest = digestPromise;
+    void digestPromise.catch(() => {
+      if (cache.lastStr === str) {
+        cache.lastStr = "";
+      }
+    });
   }
   return cache.lastDigest;
 }