From d7514feafea74f00b3c98b60d07b7e71fdbb20cf Mon Sep 17 00:00:00 2001
From: Jakob Ackermann <jakob.ackermann@overleaf.com>
Date: Mon, 23 Feb 2026 11:18:27 +0100
Subject: [PATCH] [docstore] add metrics for writes to docs collection (#31741)

* [docstore] add metrics for writes to docs collection

Co-authored-by: Brian Gough <brian.gough@overleaf.com>

* [docstore] fix import

* [docstore] use counter metric

* [docstore] add metric on lines delta

Co-authored-by: Brian Gough <brian.gough@overleaf.com>

---------

Co-authored-by: Brian Gough <brian.gough@overleaf.com>
GitOrigin-RevId: 4662c5862315c800cb7b4d57bef60e08fbe7ba59
---
 services/docstore/app/js/DocManager.js             | 14 ++++++++++++++
 services/docstore/app/js/MongoManager.js           | 11 ++++++++++-
 services/docstore/app/js/mongodb.js                |  3 ++-
 .../docstore/test/unit/js/MongoManager.test.js     |  5 ++++-
 4 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/services/docstore/app/js/DocManager.js b/services/docstore/app/js/DocManager.js
index e1ca8b0579..56a3a7c90d 100644
--- a/services/docstore/app/js/DocManager.js
+++ b/services/docstore/app/js/DocManager.js
@@ -6,6 +6,7 @@ import DocArchive from './DocArchiveManager.js'
 import RangeManager from './RangeManager.js'
 import Settings from '@overleaf/settings'
 import { setTimeout } from 'node:timers/promises'
+import Metrics from '@overleaf/metrics'
 
 /**
  * @import { Document } from 'mongodb'
@@ -255,6 +256,19 @@ const DocManager = {
         })
       }
       updateLines = !_.isEqual(doc.lines, lines)
+      if (doc.lines.length === lines.length) {
+        Metrics.inc('mongo_docs_update_delta', 1, {
+          status: 'same-line-length',
+        })
+      } else if (doc.lines.length > lines.length) {
+        Metrics.inc('mongo_docs_update_delta', 1, {
+          status: 'smaller-line-length',
+        })
+      } else if (doc.lines.length < lines.length) {
+        Metrics.inc('mongo_docs_update_delta', 1, {
+          status: 'larger-line-length',
+        })
+      }
       updateVersion = doc.version !== version
       updateRanges = RangeManager.shouldUpdateRanges(doc.ranges, ranges)
     }
diff --git a/services/docstore/app/js/MongoManager.js b/services/docstore/app/js/MongoManager.js
index 1725747b3c..5e4110dace 100644
--- a/services/docstore/app/js/MongoManager.js
+++ b/services/docstore/app/js/MongoManager.js
@@ -1,8 +1,9 @@
 import mongodb from './mongodb.js'
 import Settings from '@overleaf/settings'
 import Errors from './Errors.js'
+import Metrics from '@overleaf/metrics'
 
-const { db, ObjectId } = mongodb
+const { db, ObjectId, BSON } = mongodb
 
 const ARCHIVING_LOCK_DURATION_MS = Settings.archivingLockDurationMs
 
@@ -98,6 +99,8 @@ async function upsertIntoDocCollection(projectId, docId, previousRev, updates) {
     if (updates.lines || updates.ranges) {
       update.$inc = { rev: 1 }
     }
+    const payloadSize = BSON.calculateObjectSize(update)
+    Metrics.count('mongo_docs_write', payloadSize, 1, { method: 'update' })
     const result = await db.docs.updateOne(
       {
         _id: new ObjectId(docId),
@@ -110,6 +113,8 @@ async function upsertIntoDocCollection(projectId, docId, previousRev, updates) {
       throw new Errors.DocRevValueError()
     }
   } else {
+    const payloadSize = BSON.calculateObjectSize(updates)
+    Metrics.count('mongo_docs_write', payloadSize, 1, { method: 'insert' })
     try {
       await db.docs.insertOne({
         _id: new ObjectId(docId),
@@ -129,6 +134,8 @@ async function upsertIntoDocCollection(projectId, docId, previousRev, updates) {
 }
 
 async function patchDoc(projectId, docId, meta) {
+  const payloadSize = BSON.calculateObjectSize(meta)
+  Metrics.count('mongo_docs_write', payloadSize, 1, { method: 'patch' })
   await db.docs.updateOne(
     {
       _id: new ObjectId(docId),
@@ -195,6 +202,8 @@ async function restoreArchivedDoc(projectId, docId, archivedDoc) {
       inS3: true,
     },
   }
+  const payloadSize = BSON.calculateObjectSize(update)
+  Metrics.count('mongo_docs_write', payloadSize, 1, { method: 'restore' })
   const result = await db.docs.updateOne(query, update)
 
   if (result.matchedCount === 0) {
diff --git a/services/docstore/app/js/mongodb.js b/services/docstore/app/js/mongodb.js
index 6ddb183588..9bd0388f81 100644
--- a/services/docstore/app/js/mongodb.js
+++ b/services/docstore/app/js/mongodb.js
@@ -6,7 +6,7 @@ import Settings from '@overleaf/settings'
 import MongoUtils from '@overleaf/mongo-utils'
 import mongodb from 'mongodb-legacy'
 
-const { MongoClient, ObjectId } = mongodb
+const { MongoClient, ObjectId, BSON } = mongodb
 
 const mongoClient = new MongoClient(Settings.mongo.url, Settings.mongo.options)
 const mongoDb = mongoClient.db()
@@ -25,5 +25,6 @@ export default {
   db,
   mongoClient,
   ObjectId,
+  BSON,
   cleanupTestDatabase,
 }
diff --git a/services/docstore/test/unit/js/MongoManager.test.js b/services/docstore/test/unit/js/MongoManager.test.js
index a6d2359127..df6bb8a8d3 100644
--- a/services/docstore/test/unit/js/MongoManager.test.js
+++ b/services/docstore/test/unit/js/MongoManager.test.js
@@ -1,9 +1,11 @@
 import sinon from 'sinon'
-import { ObjectId } from 'mongodb-legacy'
+import mongodb from 'mongodb-legacy'
 import path from 'node:path'
 import { assert, beforeEach, describe, expect, it, vi } from 'vitest'
 import Errors from '../../../app/js/Errors.js'
 
+const { ObjectId, BSON } = mongodb
+
 const modulePath = path.join(
   import.meta.dirname,
   '../../../app/js/MongoManager'
@@ -22,6 +24,7 @@ describe('MongoManager', () => {
       default: {
         db: ctx.db,
         ObjectId,
+        BSON,
       },
     }))