added cron job to log collection sizes

backend/src/jobs/index.ts

@@ -1,4 +1,5 @@
 import updateLeaderboards from "./update-leaderboards";
 import deleteOldLogs from "./delete-old-logs";
+import logCollectionSizes from "./log-collection-sizes";
 
-export default [updateLeaderboards, deleteOldLogs];
+export default [updateLeaderboards, deleteOldLogs, logCollectionSizes];

backend/src/jobs/log-collection-sizes.ts

@@ -0,0 +1,25 @@
+import { CronJob } from "cron";
+import * as db from "../init/db";
+import * as Prometheus from "../utils/prometheus";
+
+const CRON_SCHEDULE = "0 0 * * * *";
+
+function main(): void {
+  Promise.all([
+    set("ape-keys"),
+    set("configs"),
+    set("errors"),
+    set("logs"),
+    set("presets"),
+    set("reports"),
+    set("results"),
+    set("users"),
+  ]);
+}
+
+async function set(collection: string): Promise<void> {
+  const size = await db.collection(collection).estimatedDocumentCount();
+  Prometheus.setCollectionSize(collection, size);
+}
+
+export default new CronJob(CRON_SCHEDULE, main);

backend/src/utils/prometheus.ts

@@ -267,3 +267,13 @@ const uidRequestCount = new Counter({
 export function recordRequestForUid(uid: string): void {
   uidRequestCount.inc({ uid });
 }
+
+const collectionSize = new Gauge({
+  name: "db_collection_size",
+  help: "Size of a collection",
+  labelNames: ["collection"],
+});
+
+export function setCollectionSize(collection: string, size: number): void {
+  collectionSize.set({ collection }, size);
+}