perf(cache): reuse GitHub content with transactional visibility revisions

drizzle/0030_github_repository_visibility_revision.sql

@@ -0,0 +1,32 @@
+-- Public snapshots also depend on current repository visibility, before projection.
+CREATE FUNCTION advance_github_repository_visibility_revision() RETURNS trigger
+LANGUAGE plpgsql SET search_path = public AS $$
+BEGIN
+  IF EXISTS (
+    SELECT 1 FROM previous_repositories previous
+    JOIN current_repositories current USING (id)
+    WHERE previous.visibility IS DISTINCT FROM current.visibility
+      AND EXISTS (
+        SELECT 1 FROM github_activity_snapshots snapshots
+        WHERE snapshots.repository_id = current.id
+      )
+  ) THEN
+    -- Advance once per statement, after all repository rows have been updated.
+    UPDATE github_public_feed_head
+    SET feed_revision = feed_revision + 1,
+        head_content_revision = head_content_revision + 1,
+        ordering_revision = ordering_revision + 1,
+        last_published_at = now()
+    WHERE id = true;
+    IF NOT FOUND THEN RAISE EXCEPTION 'The GitHub public feed head is missing'; END IF;
+  END IF;
+  RETURN NULL;
+END;
+$$;
+--> statement-breakpoint
+CREATE TRIGGER advance_github_repository_visibility_revision
+AFTER UPDATE ON github_repositories
+REFERENCING OLD TABLE AS previous_repositories NEW TABLE AS current_repositories
+FOR EACH STATEMENT EXECUTE FUNCTION advance_github_repository_visibility_revision();
+--> statement-breakpoint
+REVOKE ALL ON FUNCTION advance_github_repository_visibility_revision() FROM PUBLIC;