diff --git a/services/document-updater/app.js b/services/document-updater/app.js
index 420daddafc..2b203afaf2 100644
--- a/services/document-updater/app.js
+++ b/services/document-updater/app.js
@@ -205,7 +205,7 @@ app.use((error, req, res, next) => {
   if (error instanceof Errors.NotFoundError) {
     return res.sendStatus(404)
   } else if (error instanceof Errors.OpRangeNotAvailableError) {
-    return res.sendStatus(422) // Unprocessable Entity
+    return res.status(422).json(error.info)
   } else if (error instanceof Errors.FileTooLargeError) {
     return res.sendStatus(413)
   } else if (error.statusCode === 413) {
diff --git a/services/document-updater/app/js/Errors.js b/services/document-updater/app/js/Errors.js
index c441af4db3..a43f69ad35 100644
--- a/services/document-updater/app/js/Errors.js
+++ b/services/document-updater/app/js/Errors.js
@@ -1,51 +1,12 @@
-/* eslint-disable
-    no-proto,
-    no-unused-vars,
-*/
-// TODO: This file was created by bulk-decaffeinate.
-// Fix any style issues and re-enable lint.
-let Errors
-function NotFoundError(message) {
-  const error = new Error(message)
-  error.name = 'NotFoundError'
-  error.__proto__ = NotFoundError.prototype
-  return error
-}
-NotFoundError.prototype.__proto__ = Error.prototype
+const OError = require('@overleaf/o-error')
 
-function OpRangeNotAvailableError(message) {
-  const error = new Error(message)
-  error.name = 'OpRangeNotAvailableError'
-  error.__proto__ = OpRangeNotAvailableError.prototype
-  return error
-}
-OpRangeNotAvailableError.prototype.__proto__ = Error.prototype
+class NotFoundError extends OError {}
+class OpRangeNotAvailableError extends OError {}
+class ProjectStateChangedError extends OError {}
+class DeleteMismatchError extends OError {}
+class FileTooLargeError extends OError {}
 
-function ProjectStateChangedError(message) {
-  const error = new Error(message)
-  error.name = 'ProjectStateChangedError'
-  error.__proto__ = ProjectStateChangedError.prototype
-  return error
-}
-ProjectStateChangedError.prototype.__proto__ = Error.prototype
-
-function DeleteMismatchError(message) {
-  const error = new Error(message)
-  error.name = 'DeleteMismatchError'
-  error.__proto__ = DeleteMismatchError.prototype
-  return error
-}
-DeleteMismatchError.prototype.__proto__ = Error.prototype
-
-function FileTooLargeError(message) {
-  const error = new Error(message)
-  error.name = 'FileTooLargeError'
-  error.__proto__ = FileTooLargeError.prototype
-  return error
-}
-FileTooLargeError.prototype.__proto__ = Error.prototype
-
-module.exports = Errors = {
+module.exports = {
   NotFoundError,
   OpRangeNotAvailableError,
   ProjectStateChangedError,
diff --git a/services/document-updater/app/js/HttpController.js b/services/document-updater/app/js/HttpController.js
index 92f5ab6daa..28411061dc 100644
--- a/services/document-updater/app/js/HttpController.js
+++ b/services/document-updater/app/js/HttpController.js
@@ -44,6 +44,7 @@ function getDoc(req, res, next) {
         ops,
         ranges,
         pathname,
+        ttlInS: RedisManager.DOC_OPS_TTL,
       })
     }
   )
diff --git a/services/document-updater/app/js/ProjectManager.js b/services/document-updater/app/js/ProjectManager.js
index 35925cc3f7..781ed0e168 100644
--- a/services/document-updater/app/js/ProjectManager.js
+++ b/services/document-updater/app/js/ProjectManager.js
@@ -149,7 +149,7 @@ function getProjectDocsAndFlushIfOld(
       // we can't return docs if project structure has changed
       if (projectStateChanged) {
         return callback(
-          Errors.ProjectStateChangedError('project state changed')
+          new Errors.ProjectStateChangedError('project state changed')
         )
       }
       // project structure hasn't changed, return doc content from redis
diff --git a/services/document-updater/app/js/RealTimeRedisManager.js b/services/document-updater/app/js/RealTimeRedisManager.js
index 72713e3ffa..9f7465acb8 100644
--- a/services/document-updater/app/js/RealTimeRedisManager.js
+++ b/services/document-updater/app/js/RealTimeRedisManager.js
@@ -38,6 +38,7 @@ const RealTimeRedisManager = {
     // the MULTI's operations are all done on the same node in a
     // cluster environment.
     const multi = rclient.multi()
+    multi.llen(Keys.pendingUpdates({ doc_id: docId }))
     multi.lrange(
       Keys.pendingUpdates({ doc_id: docId }),
       0,
@@ -49,19 +50,23 @@ const RealTimeRedisManager = {
       -1
     )
     return multi.exec(function (error, replys) {
-      let jsonUpdate
       if (error != null) {
         return callback(error)
       }
-      const jsonUpdates = replys[0]
-      for (jsonUpdate of Array.from(jsonUpdates)) {
+      const [llen, jsonUpdates, _trimResult] = replys
+      metrics.histogram(
+        'redis.pendingUpdates.llen',
+        llen,
+        [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 50, 75, 100]
+      )
+      for (const jsonUpdate of jsonUpdates) {
         // record metric for each update removed from queue
         metrics.summary('redis.pendingUpdates', jsonUpdate.length, {
           status: 'pop',
         })
       }
       const updates = []
-      for (jsonUpdate of Array.from(jsonUpdates)) {
+      for (const jsonUpdate of jsonUpdates) {
         let update
         try {
           update = JSON.parse(jsonUpdate)
@@ -78,6 +83,33 @@ const RealTimeRedisManager = {
     return rclient.llen(Keys.pendingUpdates({ doc_id: docId }), callback)
   },
 
+  sendCanaryAppliedOp({ projectId, docId, op }) {
+    const ack = JSON.stringify({ v: op.v, doc: docId }).length
+    // Updates with op.dup===true will not get sent to other clients, they only get acked.
+    const broadcast = op.dup ? 0 : JSON.stringify(op).length
+
+    const payload = JSON.stringify({
+      message: 'canary-applied-op',
+      payload: {
+        ack,
+        broadcast,
+        docId,
+        projectId,
+        source: op.meta.source,
+      },
+    })
+
+    // Publish on the editor-events channel of the project as real-time already listens to that before completing the connection startup.
+
+    // publish on separate channels for individual projects and docs when
+    // configured (needs realtime to be configured for this too).
+    if (Settings.publishOnIndividualChannels) {
+      return pubsubClient.publish(`editor-events:${projectId}`, payload)
+    } else {
+      return pubsubClient.publish('editor-events', payload)
+    }
+  },
+
   sendData(data) {
     // create a unique message id using a counter
     const messageId = `doc:${HOST}:${RND}-${COUNT++}`
diff --git a/services/document-updater/app/js/RedisManager.js b/services/document-updater/app/js/RedisManager.js
index 40ce658b9c..0d2dad1047 100644
--- a/services/document-updater/app/js/RedisManager.js
+++ b/services/document-updater/app/js/RedisManager.js
@@ -396,7 +396,8 @@ const RedisManager = {
 
         if (start < firstVersionInRedis || end > version) {
           error = new Errors.OpRangeNotAvailableError(
-            'doc ops range is not loaded in redis'
+            'doc ops range is not loaded in redis',
+            { firstVersionInRedis, version, ttlInS: RedisManager.DOC_OPS_TTL }
           )
           logger.debug(
             { err: error, docId, length, version, start, end },
diff --git a/services/document-updater/app/js/ShareJsDB.js b/services/document-updater/app/js/ShareJsDB.js
index 7cfeef3922..580a3d93b5 100644
--- a/services/document-updater/app/js/ShareJsDB.js
+++ b/services/document-updater/app/js/ShareJsDB.js
@@ -11,6 +11,8 @@
  * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
  */
 let ShareJsDB
+const logger = require('@overleaf/logger')
+const Metrics = require('@overleaf/metrics')
 const Keys = require('./UpdateKeys')
 const RedisManager = require('./RedisManager')
 const Errors = require('./Errors')
@@ -25,10 +27,15 @@ module.exports = ShareJsDB = class ShareJsDB {
     // ShareJS calls this detacted from the instance, so we need
     // bind it to keep our context that can access @appliedOps
     this.writeOp = this._writeOp.bind(this)
+    this.startTimeShareJsDB = performance.now()
   }
 
   getOps(docKey, start, end, callback) {
     if (start === end) {
+      Metrics.inc('transform-updates', 1, {
+        status: 'is-up-to-date',
+        path: 'sharejs',
+      })
       return callback(null, [])
     }
 
@@ -40,7 +47,60 @@ module.exports = ShareJsDB = class ShareJsDB {
     }
 
     const [projectId, docId] = Array.from(Keys.splitProjectIdAndDocId(docKey))
-    return RedisManager.getPreviousDocOps(docId, start, end, callback)
+    const timer = new Metrics.Timer(
+      'transform-updates.timing',
+      1,
+      { path: 'sharejs' },
+      [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 50, 100, 200, 500, 1000]
+    )
+    RedisManager.getPreviousDocOps(docId, start, end, (err, ops) => {
+      let status
+      if (err) {
+        if (err instanceof Errors.OpRangeNotAvailableError) {
+          status = 'out-of-range'
+        } else {
+          status = 'error'
+        }
+      } else {
+        if (ops.length === 0) {
+          status = 'fetched-zero'
+        } else {
+          status = 'fetched'
+
+          if (start === this.version && end === -1) {
+            // The sharejs processing is happening under a lock.
+            // this.version is the version as read from redis under lock.
+            // In case there are any new ops available, something bypassed the lock (or we overran it).
+            logger.warn(
+              {
+                projectId,
+                docId,
+                start,
+                nOps: ops.length,
+                timeSinceShareJsDBInit:
+                  performance.now() - this.startTimeShareJsDB,
+              },
+              'concurrent update of docOps while transforming update'
+            )
+          }
+        }
+        Metrics.histogram(
+          'transform-updates.count',
+          ops.length,
+          [
+            0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 50, 75, 100,
+            // prepare buckets for full-project history/larger buffer experiments
+            150,
+            200, 300, 400,
+          ],
+          { path: 'sharejs', status }
+        )
+      }
+
+      timer.done({ status })
+      Metrics.inc('transform-updates', 1, { status, path: 'sharejs' })
+      callback(err, ops)
+    })
   }
 
   _writeOp(docKey, opData, callback) {
diff --git a/services/document-updater/app/js/ShareJsUpdateManager.js b/services/document-updater/app/js/ShareJsUpdateManager.js
index 40a1e3b041..edac3700b7 100644
--- a/services/document-updater/app/js/ShareJsUpdateManager.js
+++ b/services/document-updater/app/js/ShareJsUpdateManager.js
@@ -128,11 +128,16 @@ const ShareJsUpdateManager = {
   },
 
   _sendOp(projectId, docId, op) {
-    return RealTimeRedisManager.sendData({
+    RealTimeRedisManager.sendData({
       project_id: projectId,
       doc_id: docId,
       op,
     })
+    RealTimeRedisManager.sendCanaryAppliedOp({
+      projectId,
+      docId,
+      op,
+    })
   },
 
   _computeHash(content) {
diff --git a/services/document-updater/test/unit/js/HttpController/HttpControllerTests.js b/services/document-updater/test/unit/js/HttpController/HttpControllerTests.js
index 35699a895f..024c5a5f63 100644
--- a/services/document-updater/test/unit/js/HttpController/HttpControllerTests.js
+++ b/services/document-updater/test/unit/js/HttpController/HttpControllerTests.js
@@ -15,7 +15,9 @@ describe('HttpController', function () {
         './ProjectManager': (this.ProjectManager = {}),
         './ProjectFlusher': { flushAllProjects() {} },
         './DeleteQueueManager': (this.DeleteQueueManager = {}),
-        './RedisManager': (this.RedisManager = {}),
+        './RedisManager': (this.RedisManager = {
+          DOC_OPS_TTL: 42,
+        }),
         './Metrics': (this.Metrics = {}),
         './Errors': Errors,
         '@overleaf/settings': { max_doc_length: 2 * 1024 * 1024 },
@@ -84,6 +86,7 @@ describe('HttpController', function () {
             ops: [],
             ranges: this.ranges,
             pathname: this.pathname,
+            ttlInS: 42,
           })
           .should.equal(true)
       })
@@ -134,6 +137,7 @@ describe('HttpController', function () {
             ops: this.ops,
             ranges: this.ranges,
             pathname: this.pathname,
+            ttlInS: 42,
           })
           .should.equal(true)
       })
diff --git a/services/document-updater/test/unit/js/RealTimeRedisManager/RealTimeRedisManagerTests.js b/services/document-updater/test/unit/js/RealTimeRedisManager/RealTimeRedisManagerTests.js
index 577f6fab25..d678c8d7a6 100644
--- a/services/document-updater/test/unit/js/RealTimeRedisManager/RealTimeRedisManagerTests.js
+++ b/services/document-updater/test/unit/js/RealTimeRedisManager/RealTimeRedisManagerTests.js
@@ -49,7 +49,10 @@ describe('RealTimeRedisManager', function () {
             .returns(Buffer.from([0x1, 0x2, 0x3, 0x4])),
         }),
         os: (this.os = { hostname: sinon.stub().returns('somehost') }),
-        './Metrics': (this.metrics = { summary: sinon.stub() }),
+        './Metrics': (this.metrics = {
+          summary: sinon.stub(),
+          histogram: sinon.stub(),
+        }),
       },
     })
 
@@ -60,6 +63,7 @@ describe('RealTimeRedisManager', function () {
 
   describe('getPendingUpdatesForDoc', function () {
     beforeEach(function () {
+      this.rclient.llen = sinon.stub()
       this.rclient.lrange = sinon.stub()
       return (this.rclient.ltrim = sinon.stub())
     })
@@ -71,9 +75,7 @@ describe('RealTimeRedisManager', function () {
           { op: [{ i: 'foo', p: 4 }] },
         ]
         this.jsonUpdates = this.updates.map(update => JSON.stringify(update))
-        this.rclient.exec = sinon
-          .stub()
-          .callsArgWith(0, null, [this.jsonUpdates])
+        this.rclient.exec = sinon.stub().yields(null, [2, this.jsonUpdates])
         return this.RealTimeRedisManager.getPendingUpdatesForDoc(
           this.doc_id,
           this.callback
@@ -103,9 +105,7 @@ describe('RealTimeRedisManager', function () {
           JSON.stringify({ op: [{ i: 'foo', p: 4 }] }),
           'broken json',
         ]
-        this.rclient.exec = sinon
-          .stub()
-          .callsArgWith(0, null, [this.jsonUpdates])
+        this.rclient.exec = sinon.stub().yields(null, [2, this.jsonUpdates])
         return this.RealTimeRedisManager.getPendingUpdatesForDoc(
           this.doc_id,
           this.callback
diff --git a/services/document-updater/test/unit/js/RedisManager/RedisManagerTests.js b/services/document-updater/test/unit/js/RedisManager/RedisManagerTests.js
index 37591d6cfe..e23964eaba 100644
--- a/services/document-updater/test/unit/js/RedisManager/RedisManagerTests.js
+++ b/services/document-updater/test/unit/js/RedisManager/RedisManagerTests.js
@@ -407,6 +407,18 @@ describe('RedisManager', function () {
           .should.equal(true)
       })
 
+      it('should send details for metrics', function () {
+        this.callback.should.have.been.calledWith(
+          sinon.match({
+            info: {
+              firstVersionInRedis: this.first_version_in_redis,
+              version: this.version,
+              ttlInS: this.RedisManager.DOC_OPS_TTL,
+            },
+          })
+        )
+      })
+
       it('should log out the problem as a debug message', function () {
         this.logger.debug.called.should.equal(true)
       })
diff --git a/services/document-updater/test/unit/js/ShareJsDB/ShareJsDBTests.js b/services/document-updater/test/unit/js/ShareJsDB/ShareJsDBTests.js
index 4ac16a8fe7..63748e3baa 100644
--- a/services/document-updater/test/unit/js/ShareJsDB/ShareJsDBTests.js
+++ b/services/document-updater/test/unit/js/ShareJsDB/ShareJsDBTests.js
@@ -26,6 +26,13 @@ describe('ShareJsDB', function () {
       requires: {
         './RedisManager': (this.RedisManager = {}),
         './Errors': Errors,
+        '@overleaf/metrics': {
+          inc: sinon.stub(),
+          histogram: sinon.stub(),
+          Timer: class Timer {
+            done() {}
+          },
+        },
       },
     })
 
@@ -89,6 +96,7 @@ describe('ShareJsDB', function () {
       beforeEach(function () {
         this.start = 35
         this.end = 42
+        this.ops = new Array(this.end - this.start)
         this.RedisManager.getPreviousDocOps = sinon
           .stub()
           .callsArgWith(3, null, this.ops)
@@ -110,6 +118,7 @@ describe('ShareJsDB', function () {
       beforeEach(function () {
         this.start = 35
         this.end = null
+        this.ops = []
         this.RedisManager.getPreviousDocOps = sinon
           .stub()
           .callsArgWith(3, null, this.ops)
diff --git a/services/document-updater/test/unit/js/ShareJsUpdateManager/ShareJsUpdateManagerTests.js b/services/document-updater/test/unit/js/ShareJsUpdateManager/ShareJsUpdateManagerTests.js
index 6fea29287f..347ac7dea6 100644
--- a/services/document-updater/test/unit/js/ShareJsUpdateManager/ShareJsUpdateManagerTests.js
+++ b/services/document-updater/test/unit/js/ShareJsUpdateManager/ShareJsUpdateManagerTests.js
@@ -33,7 +33,9 @@ describe('ShareJsUpdateManager', function () {
             return (this.rclient = { auth() {} })
           },
         },
-        './RealTimeRedisManager': (this.RealTimeRedisManager = {}),
+        './RealTimeRedisManager': (this.RealTimeRedisManager = {
+          sendCanaryAppliedOp: sinon.stub(),
+        }),
         './Metrics': (this.metrics = { inc: sinon.stub() }),
       },
       globals: {
diff --git a/services/real-time/app/js/DocumentUpdaterController.js b/services/real-time/app/js/DocumentUpdaterController.js
index c7cfa5e986..3fd22d3ebd 100644
--- a/services/real-time/app/js/DocumentUpdaterController.js
+++ b/services/real-time/app/js/DocumentUpdaterController.js
@@ -105,6 +105,11 @@ module.exports = DocumentUpdaterController = {
     if (clientList.length === 0) {
       return
     }
+
+    update.meta = update.meta || {}
+    const { tsRT: realTimeIngestionTime } = update.meta
+    delete update.meta.tsRT
+
     // send updates to clients
     logger.debug(
       {
@@ -129,6 +134,15 @@ module.exports = DocumentUpdaterController = {
             },
             'distributing update to sender'
           )
+          metrics.histogram(
+            'update-processing-time',
+            performance.now() - realTimeIngestionTime,
+            [
+              0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 50, 100, 200, 500, 1000,
+              2000, 5000, 10000,
+            ],
+            { path: 'sharejs' }
+          )
           client.emit('otUpdateApplied', { v: update.v, doc: update.doc })
         } else if (!update.dup) {
           // Duplicate ops should just be sent back to sending client for acknowledgement
diff --git a/services/real-time/app/js/DocumentUpdaterManager.js b/services/real-time/app/js/DocumentUpdaterManager.js
index 850e3a8d6f..0a9a12c99d 100644
--- a/services/real-time/app/js/DocumentUpdaterManager.js
+++ b/services/real-time/app/js/DocumentUpdaterManager.js
@@ -42,7 +42,16 @@ const DocumentUpdaterManager = {
           return callback(error)
         }
         body = body || {}
-        callback(null, body.lines, body.version, body.ranges, body.ops)
+        callback(
+          null,
+          body.lines,
+          body.version,
+          body.ranges,
+          body.ops,
+          body.ttlInS
+        )
+      } else if (res.statusCode === 422 && body?.firstVersionInRedis) {
+        callback(new ClientRequestedMissingOpsError(422, body))
       } else if ([404, 422].includes(res.statusCode)) {
         callback(new ClientRequestedMissingOpsError(res.statusCode))
       } else {
diff --git a/services/real-time/app/js/Errors.js b/services/real-time/app/js/Errors.js
index a5177be737..fea0cc643a 100644
--- a/services/real-time/app/js/Errors.js
+++ b/services/real-time/app/js/Errors.js
@@ -1,9 +1,10 @@
 const OError = require('@overleaf/o-error')
 
 class ClientRequestedMissingOpsError extends OError {
-  constructor(statusCode) {
+  constructor(statusCode, info = {}) {
     super('doc updater could not load requested ops', {
       statusCode,
+      ...info,
     })
   }
 }
diff --git a/services/real-time/app/js/WebsocketController.js b/services/real-time/app/js/WebsocketController.js
index eeaf4fe9ba..4888f56097 100644
--- a/services/real-time/app/js/WebsocketController.js
+++ b/services/real-time/app/js/WebsocketController.js
@@ -11,8 +11,28 @@ const {
   JoinLeaveEpochMismatchError,
   NotAuthorizedError,
   NotJoinedError,
+  ClientRequestedMissingOpsError,
 } = require('./Errors')
 
+const JOIN_DOC_CATCH_UP_LENGTH_BUCKETS = [
+  0, 5, 10, 25, 50, 100, 150, 200, 250, 500, 1000,
+]
+const JOIN_DOC_CATCH_UP_AGE = [
+  0,
+  1,
+  2,
+  5,
+  10,
+  20,
+  30,
+  60,
+  120,
+  240,
+  600,
+  60 * 60,
+  24 * 60 * 60,
+].map(x => x * 1000)
+
 let WebsocketController
 module.exports = WebsocketController = {
   // If the protocol version changes when the client reconnects,
@@ -195,6 +215,38 @@ module.exports = WebsocketController = {
       'client joining doc'
     )
 
+    const emitJoinDocCatchUpMetrics = (
+      status,
+      { firstVersionInRedis, version, ttlInS }
+    ) => {
+      if (fromVersion === -1) return // full joinDoc call
+      if (typeof options.age !== 'number') return // old frontend
+      if (!ttlInS) return // old document-updater pod
+
+      const isStale = options.age > ttlInS * 1000
+      const method = isStale ? 'stale' : 'recent'
+      metrics.histogram(
+        'join-doc-catch-up-length',
+        version - fromVersion,
+        JOIN_DOC_CATCH_UP_LENGTH_BUCKETS,
+        { status, method, path: client.transport }
+      )
+      if (firstVersionInRedis) {
+        metrics.histogram(
+          'join-doc-catch-up-length-extra-needed',
+          firstVersionInRedis - fromVersion,
+          JOIN_DOC_CATCH_UP_LENGTH_BUCKETS,
+          { status, method, path: client.transport }
+        )
+      }
+      metrics.histogram(
+        'join-doc-catch-up-age',
+        options.age,
+        JOIN_DOC_CATCH_UP_AGE,
+        { status, path: client.transport }
+      )
+    }
+
     WebsocketController._assertClientAuthorization(
       client,
       docId,
@@ -231,10 +283,14 @@ module.exports = WebsocketController = {
             projectId,
             docId,
             fromVersion,
-            function (error, lines, version, ranges, ops) {
+            function (error, lines, version, ranges, ops, ttlInS) {
               if (error) {
+                if (error instanceof ClientRequestedMissingOpsError) {
+                  emitJoinDocCatchUpMetrics('missing', error.info)
+                }
                 return callback(error)
               }
+              emitJoinDocCatchUpMetrics('success', { version, ttlInS })
               if (client.disconnected) {
                 metrics.inc('editor.join-doc.disconnected', 1, {
                   status: 'after-doc-updater-call',
@@ -503,6 +559,7 @@ module.exports = WebsocketController = {
         }
         update.meta.source = client.publicId
         update.meta.user_id = userId
+        update.meta.tsRT = performance.now()
         metrics.inc('editor.doc-update', 0.3, { status: client.transport })
 
         logger.debug(
diff --git a/services/real-time/app/js/WebsocketLoadBalancer.js b/services/real-time/app/js/WebsocketLoadBalancer.js
index 4c9bb96b5a..ebf20fa11f 100644
--- a/services/real-time/app/js/WebsocketLoadBalancer.js
+++ b/services/real-time/app/js/WebsocketLoadBalancer.js
@@ -1,5 +1,6 @@
 const Settings = require('@overleaf/settings')
 const logger = require('@overleaf/logger')
+const Metrics = require('@overleaf/metrics')
 const RedisClientManager = require('./RedisClientManager')
 const SafeJsonParse = require('./SafeJsonParse')
 const EventLogger = require('./EventLogger')
@@ -24,6 +25,11 @@ const RESTRICTED_USER_MESSAGE_TYPE_PASS_LIST = [
   'toggle-track-changes',
   'projectRenamedOrDeletedByExternalSource',
 ]
+const BANDWIDTH_BUCKETS = [0]
+// 64 bytes ... 8MB
+for (let i = 5; i <= 22; i++) {
+  BANDWIDTH_BUCKETS.push(2 << i)
+}
 
 let WebsocketLoadBalancer
 module.exports = WebsocketLoadBalancer = {
@@ -139,6 +145,31 @@ module.exports = WebsocketLoadBalancer = {
         for (const client of clientList) {
           ConnectedUsersManager.refreshClient(message.room_id, client.publicId)
         }
+      } else if (message.message === 'canary-applied-op') {
+        const { ack, broadcast, source, projectId, docId } = message.payload
+
+        const estimateBandwidth = (room, path) => {
+          const seen = new Set()
+          for (const client of io.sockets.clients(room)) {
+            if (seen.has(client.id)) continue
+            seen.add(client.id)
+            let v = client.id === source ? ack : broadcast
+            if (v === 0) {
+              // Acknowledgements with update.dup===true will not get sent to other clients.
+              continue
+            }
+            v += `5:::{"name":"otUpdateApplied","args":[]}`.length
+            Metrics.histogram(
+              'estimated-applied-ops-bandwidth',
+              v,
+              BANDWIDTH_BUCKETS,
+              { path }
+            )
+          }
+        }
+
+        estimateBandwidth(projectId, 'per-project')
+        estimateBandwidth(docId, 'per-doc')
       } else if (message.room_id) {
         if (message._id && Settings.checkEventOrder) {
           const status = EventLogger.checkEventOrder(
diff --git a/services/real-time/test/acceptance/js/ApplyUpdateTests.js b/services/real-time/test/acceptance/js/ApplyUpdateTests.js
index 2b208bbb66..c3e47ed409 100644
--- a/services/real-time/test/acceptance/js/ApplyUpdateTests.js
+++ b/services/real-time/test/acceptance/js/ApplyUpdateTests.js
@@ -129,7 +129,7 @@ describe('applyOtUpdate', function () {
           let [update] = Array.from(rest[0])
           update = JSON.parse(update)
           update.op.should.deep.equal(this.update.op)
-          update.meta.should.deep.equal({
+          update.meta.should.include({
             source: this.client.publicId,
             user_id: this.user_id,
           })
@@ -408,7 +408,7 @@ describe('applyOtUpdate', function () {
           let [update] = Array.from(rest[0])
           update = JSON.parse(update)
           update.op.should.deep.equal(this.comment_update.op)
-          update.meta.should.deep.equal({
+          update.meta.should.include({
             source: this.client.publicId,
             user_id: this.user_id,
           })
diff --git a/services/real-time/test/unit/js/DocumentUpdaterControllerTests.js b/services/real-time/test/unit/js/DocumentUpdaterControllerTests.js
index 59e73bf6a8..31846f65b4 100644
--- a/services/real-time/test/unit/js/DocumentUpdaterControllerTests.js
+++ b/services/real-time/test/unit/js/DocumentUpdaterControllerTests.js
@@ -55,7 +55,10 @@ describe('DocumentUpdaterController', function () {
         }),
         './EventLogger': (this.EventLogger = { checkEventOrder: sinon.stub() }),
         './HealthCheckManager': { check: sinon.stub() },
-        '@overleaf/metrics': (this.metrics = { inc: sinon.stub() }),
+        '@overleaf/metrics': (this.metrics = {
+          inc: sinon.stub(),
+          histogram: sinon.stub(),
+        }),
         './RoomManager': (this.RoomManager = {
           eventSource: sinon.stub().returns(this.RoomEvents),
         }),
diff --git a/services/web/frontend/js/features/ide-react/editor/document-container.ts b/services/web/frontend/js/features/ide-react/editor/document-container.ts
index 6b1b5f43f0..6bc7322a1b 100644
--- a/services/web/frontend/js/features/ide-react/editor/document-container.ts
+++ b/services/web/frontend/js/features/ide-react/editor/document-container.ts
@@ -459,7 +459,7 @@ export class DocumentContainer extends EventEmitter {
         'joinDoc',
         this.doc_id,
         this.doc.getVersion(),
-        { encodeRanges: true },
+        { encodeRanges: true, age: this.doc.getTimeSinceLastServerActivity() },
         (error, docLines, version, updates, ranges) => {
           if (error) {
             callback?.(error)
diff --git a/services/web/frontend/js/features/ide-react/editor/share-js-doc.ts b/services/web/frontend/js/features/ide-react/editor/share-js-doc.ts
index 1363e0c55b..2bb3a08cc9 100644
--- a/services/web/frontend/js/features/ide-react/editor/share-js-doc.ts
+++ b/services/web/frontend/js/features/ide-react/editor/share-js-doc.ts
@@ -257,6 +257,10 @@ export class ShareJsDoc extends EventEmitter {
     return this._doc.version
   }
 
+  getTimeSinceLastServerActivity() {
+    return Math.floor(performance.now() - this._doc.lastServerActivity)
+  }
+
   getType() {
     return this.type
   }
diff --git a/services/web/frontend/js/vendor/libs/sharejs.js b/services/web/frontend/js/vendor/libs/sharejs.js
index 5a218f78f5..6b9ea123d7 100644
--- a/services/web/frontend/js/vendor/libs/sharejs.js
+++ b/services/web/frontend/js/vendor/libs/sharejs.js
@@ -909,6 +909,7 @@ export const { Doc } = (() => {
         openData = {};
       }
       this.version = openData.v;
+      this.lastServerActivity = performance.now()
       this.snapshot = openData.snaphot;
       if (openData.type) {
         this._setType(openData.type);
@@ -1169,6 +1170,7 @@ export const { Doc } = (() => {
             }
 
             this.version++;
+            this.lastServerActivity = performance.now()
             this.emit('acknowledge', oldInflightOp);
             var _iteratorNormalCompletion13 = true;
             var _didIteratorError13 = false;
@@ -1236,6 +1238,7 @@ export const { Doc } = (() => {
           }
 
           this.version++;
+          this.lastServerActivity = performance.now()
           // Finally, apply the op to @snapshot and trigger any event listeners
           return this._otApply(docOp, true, msg);
         } else if (msg.meta) {