From 1a4fa38b2e9e146bdbcff1dd05b060bf1ffe4a0d Mon Sep 17 00:00:00 2001 From: John McLear Date: Fri, 15 May 2026 21:52:02 +0100 Subject: [PATCH] =?UTF-8?q?feat(scaling):=20NEW=5FCHANGES=5FBATCH=20?= =?UTF-8?q?=E2=80=94=20pack=20multi-rev=20fan-out=20into=20one=20emit?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Identified by the #7756 scaling dive (PR #7765) and confirmed by the engine.io transport investigation in #7767: socket.io's polling transport batches multiple queued packets into a single HTTP response, but the WebSocket transport sends one frame per packet — even when the engine.io socket has several packets buffered. At 200 concurrent authors that's ~6,600 individual WS frames/sec/client, starving the apply path of CPU. This PR addresses the cost at the application layer: when a recipient is more than one revision behind, the server packs all queued revisions into a single NEW_CHANGES_BATCH message instead of emitting NEW_CHANGES once per rev. The wire payload is the same information, just consolidated. Feature-flagged: - settings.newChangesBatch defaults to false. Production behaviour is unchanged. - When enabled, server emits NEW_CHANGES_BATCH iff a recipient has >1 rev pending; single-rev fan-outs stay as NEW_CHANGES (no framing overhead for the steady-state case). Clients are forward-compatible: both collab_client.ts (live editor) and broadcast.ts (timeslider) now accept either message type and normalise to a list. Newly-built clients work against any server regardless of the flag; the back-compat hazard is enabling the flag on a server while old clients are still connected (documented in the setting's prose). Tests: src/tests/backend-new/specs/new-changes-batch.test.ts pins the server's wire-format decision. 4/4 new + 5/5 existing prom-instruments stay green. Co-Authored-By: Claude Opus 4.7 (1M context) --- settings.json.template | 12 +++ src/node/handler/PadMessageHandler.ts | 69 +++++++++++++----- src/node/prom-instruments.ts | 1 + src/node/utils/Settings.ts | 16 ++++ src/static/js/broadcast.ts | 22 ++++-- src/static/js/collab_client.ts | 23 ++++-- src/static/js/types/SocketIOMessage.ts | 14 ++++ .../specs/new-changes-batch.test.ts | 73 +++++++++++++++++++ 8 files changed, 194 insertions(+), 36 deletions(-) create mode 100644 src/tests/backend-new/specs/new-changes-batch.test.ts diff --git a/settings.json.template b/settings.json.template index e88e82a36..87bcc3f9a 100644 --- a/settings.json.template +++ b/settings.json.template @@ -733,6 +733,18 @@ */ "loadTest": false, + /* + * Pack multiple NEW_CHANGES revisions into a single NEW_CHANGES_BATCH emit + * per recipient when a fan-out has more than one revision to catch up + * (#7756 lever 3b). Reduces engine.io packet count under high pad + * concurrency, especially on the WebSocket transport. + * + * WARNING: enabling this requires all connected clients to understand + * NEW_CHANGES_BATCH. Old clients will silently fail to apply batched + * revisions. Coordinate the rollout. + */ + "newChangesBatch": false, + /** * Disable dump of objects preventing a clean exit */ diff --git a/src/node/handler/PadMessageHandler.ts b/src/node/handler/PadMessageHandler.ts index 3a27a7ac7..60b0d8537 100644 --- a/src/node/handler/PadMessageHandler.ts +++ b/src/node/handler/PadMessageHandler.ts @@ -964,11 +964,29 @@ exports.updatePadClients = async (pad: PadType) => { // but benefit of reusing cached revision object is HUGE const revCache:MapArrayType = {}; + // When `settings.newChangesBatch` is true and a recipient is more than one + // revision behind, pack the queued revisions into a single NEW_CHANGES_BATCH + // emit per recipient. The engine.io WebSocket transport sends one frame per + // packet (the polling transport already batches at the HTTP-response layer), + // so reducing the packet count translates directly into fewer system calls + // on the server and fewer onmessage callbacks on the client. + const batchEnabled = settings.newChangesBatch === true; + await Promise.all(roomSockets.map(async (socket) => { const sessioninfo = sessioninfos[socket.id]; // The user might have disconnected since _getRoomSockets() was called. if (sessioninfo == null) return; + // Collect all queued revisions for this socket. + const pending: Array<{ + newRev: number; + changeset: string; + apool: unknown; + author: string; + currentTime: number; + timeDelta: number; + }> = []; + while (sessioninfo.rev < pad.getHeadRevisionNumber()) { const r = sessioninfo.rev + 1; let revision = revCache[r]; @@ -980,30 +998,41 @@ exports.updatePadClients = async (pad: PadType) => { const author = revision.meta.author; const revChangeset = revision.changeset; const currentTime = revision.meta.timestamp; - const forWire = prepareForWire(revChangeset, pad.pool); - const msg = { - type: 'COLLABROOM', - data: { - type: 'NEW_CHANGES', - newRev: r, - changeset: forWire.translated, - apool: forWire.pool, - author, - currentTime, - timeDelta: currentTime - sessioninfo.time, - }, - }; - try { - socket.emit('message', msg); - recordSocketEmit('NEW_CHANGES'); - } catch (err:any) { - messageLogger.error(`Failed to notify user of new revision: ${err.stack || err}`); - return; - } + + pending.push({ + newRev: r, + changeset: forWire.translated, + apool: forWire.pool, + author, + currentTime, + timeDelta: currentTime - sessioninfo.time, + }); sessioninfo.time = currentTime; sessioninfo.rev = r; } + + if (pending.length === 0) return; + + try { + if (batchEnabled && pending.length > 1) { + socket.emit('message', { + type: 'COLLABROOM', + data: {type: 'NEW_CHANGES_BATCH', changes: pending}, + }); + recordSocketEmit('NEW_CHANGES_BATCH'); + } else { + for (const change of pending) { + socket.emit('message', { + type: 'COLLABROOM', + data: {type: 'NEW_CHANGES', ...change}, + }); + recordSocketEmit('NEW_CHANGES'); + } + } + } catch (err: any) { + messageLogger.error(`Failed to notify user of new revision: ${err.stack || err}`); + } })); }; diff --git a/src/node/prom-instruments.ts b/src/node/prom-instruments.ts index ebb54018d..fd998c45f 100644 --- a/src/node/prom-instruments.ts +++ b/src/node/prom-instruments.ts @@ -40,6 +40,7 @@ export const padUsersGauge = new client.Gauge({ // state. const KNOWN_TYPES = new Set([ 'NEW_CHANGES', + 'NEW_CHANGES_BATCH', 'ACCEPT_COMMIT', 'CHAT_MESSAGE', 'CLIENT_VARS', diff --git a/src/node/utils/Settings.ts b/src/node/utils/Settings.ts index 974130041..f74eeecdb 100644 --- a/src/node/utils/Settings.ts +++ b/src/node/utils/Settings.ts @@ -272,6 +272,7 @@ export type SettingsType = { automaticReconnectionTimeout: number, loadTest: boolean, scalingDiveMetrics: boolean, + newChangesBatch: boolean, dumpOnUncleanExit: boolean, indentationOnNewLine: boolean, logconfig: any | null, @@ -658,6 +659,21 @@ const settings: SettingsType = { * production deployments aren't paying for instrumentation they don't use. */ scalingDiveMetrics: false, + /** + * Pack multiple NEW_CHANGES revisions into a single NEW_CHANGES_BATCH emit + * per recipient when a fan-out has more than one revision to catch up + * (#7756 lever 3b). Reduces engine.io packet count under high pad + * concurrency, especially on the WebSocket transport, which sends one + * frame per packet (the polling transport already batches naturally). + * + * Requires clients to recognise the NEW_CHANGES_BATCH message type. New + * clients are forward-compatible (they handle both NEW_CHANGES and + * NEW_CHANGES_BATCH). Old clients connecting to a server with this enabled + * would fail to apply batched revisions, so coordinate the rollout. + * + * 0/false (default) preserves legacy per-revision emit behaviour. + */ + newChangesBatch: false, /** * Disable dump of objects preventing a clean exit */ diff --git a/src/static/js/broadcast.ts b/src/static/js/broadcast.ts index 8551f1d0c..01262e49a 100644 --- a/src/static/js/broadcast.ts +++ b/src/static/js/broadcast.ts @@ -493,17 +493,23 @@ const loadBroadcastJS = (socket, sendSocketMsg, fireWhenAllScriptsAreLoaded, Bro if (obj.type === 'COLLABROOM') { obj = obj.data; - if (obj.type === 'NEW_CHANGES') { - const changeset = moveOpsToNewPool( - obj.changeset, (new AttribPool()).fromJsonable(obj.apool), padContents.apool); + if (obj.type === 'NEW_CHANGES' || obj.type === 'NEW_CHANGES_BATCH') { + // NEW_CHANGES_BATCH (#7756 lever 3b) carries an array of revisions + // in one emit. Each revision has the same shape as the legacy + // single-rev message; apply in order. + const changes = obj.type === 'NEW_CHANGES_BATCH' ? obj.changes : [obj]; + for (const change of changes) { + const changeset = moveOpsToNewPool( + change.changeset, (new AttribPool()).fromJsonable(change.apool), padContents.apool); - let changesetBack = inverse( - obj.changeset, padContents.currentLines, padContents.alines, padContents.apool); + let changesetBack = inverse( + change.changeset, padContents.currentLines, padContents.alines, padContents.apool); - changesetBack = moveOpsToNewPool( - changesetBack, (new AttribPool()).fromJsonable(obj.apool), padContents.apool); + changesetBack = moveOpsToNewPool( + changesetBack, (new AttribPool()).fromJsonable(change.apool), padContents.apool); - loadedNewChangeset(changeset, changesetBack, obj.newRev - 1, obj.timeDelta); + loadedNewChangeset(changeset, changesetBack, change.newRev - 1, change.timeDelta); + } } else if (obj.type === 'NEW_AUTHORDATA') { const authorMap = {}; authorMap[obj.author] = obj.data; diff --git a/src/static/js/collab_client.ts b/src/static/js/collab_client.ts index c90f92e80..672280959 100644 --- a/src/static/js/collab_client.ts +++ b/src/static/js/collab_client.ts @@ -188,7 +188,12 @@ const getCollabClient = (ace2editor, serverVars, initialUserInfo, options, _pad) if (wrapper.type !== 'COLLABROOM' && wrapper.type !== 'CUSTOM') return; const msg = wrapper.data; - if (msg.type === 'NEW_CHANGES') { + if (msg.type === 'NEW_CHANGES' || msg.type === 'NEW_CHANGES_BATCH') { + // NEW_CHANGES_BATCH (added in #7756 lever 3b) carries an array of + // revisions in one emit. Each revision has the same shape as the + // legacy single-rev message, so we normalise to a list and apply in + // order, sharing the same compose-safety await. + const changes = msg.type === 'NEW_CHANGES_BATCH' ? msg.changes : [msg]; serverMessageTaskQueue.enqueue(async () => { // Avoid updating the DOM while the user is composing a character. Notes about this `await`: // * `await null;` is equivalent to `await Promise.resolve(null);`, so if the user is not @@ -198,14 +203,16 @@ const getCollabClient = (ace2editor, serverVars, initialUserInfo, options, _pad) // possible, that the chances are so small or the consequences so minor that it's not // worth addressing). await editor.getInInternationalComposition(); - const {newRev, changeset, author = '', apool} = msg; - if (newRev !== (rev + 1)) { - window.console.warn(`bad message revision on NEW_CHANGES: ${newRev} not ${rev + 1}`); - // setChannelState("DISCONNECTED", "badmessage_newchanges"); - return; + for (const change of changes) { + const {newRev, changeset, author = '', apool} = change; + if (newRev !== (rev + 1)) { + window.console.warn(`bad message revision on ${msg.type}: ${newRev} not ${rev + 1}`); + // setChannelState("DISCONNECTED", "badmessage_newchanges"); + return; + } + rev = newRev; + editor.applyChangesToBase(changeset, author, apool); } - rev = newRev; - editor.applyChangesToBase(changeset, author, apool); }); } else if (msg.type === 'ACCEPT_COMMIT') { serverMessageTaskQueue.enqueue(() => { diff --git a/src/static/js/types/SocketIOMessage.ts b/src/static/js/types/SocketIOMessage.ts index 914c5c472..922363ae6 100644 --- a/src/static/js/types/SocketIOMessage.ts +++ b/src/static/js/types/SocketIOMessage.ts @@ -128,6 +128,20 @@ export type ClientNewChanges = { payload?: ClientNewChanges } +export type NewChangesItem = { + apool: AttributePool, + author: string, + changeset: string, + currentTime: number, + newRev: number, + timeDelta: number, +} + +export type ClientNewChangesBatch = { + type: 'NEW_CHANGES_BATCH', + changes: NewChangesItem[], +} + export type ClientAcceptCommitMessage = { type: 'ACCEPT_COMMIT' newRev: number diff --git a/src/tests/backend-new/specs/new-changes-batch.test.ts b/src/tests/backend-new/specs/new-changes-batch.test.ts new file mode 100644 index 000000000..6c22099e5 --- /dev/null +++ b/src/tests/backend-new/specs/new-changes-batch.test.ts @@ -0,0 +1,73 @@ +// Unit coverage for the NEW_CHANGES_BATCH server-side packing +// (#7756 lever 3b). Server-side concern only — verifies that the +// pad fan-out emits one batch per recipient when multiple revs queue +// up and the feature flag is on, and falls back to per-rev emits +// otherwise. Client-side coverage lives in the existing Playwright +// flow tests; this test pins the wire-format decision. + +import {describe, it, expect, beforeEach, afterEach} from 'vitest'; +import settings from '../../../node/utils/Settings'; + +const ORIGINAL_FLAG = settings.newChangesBatch; + +beforeEach(() => { settings.newChangesBatch = false; }); +afterEach(() => { settings.newChangesBatch = ORIGINAL_FLAG; }); + +// The decision the new code makes is small and pure: given a `pending` +// array of N >= 1 revisions and the feature flag, emit one +// NEW_CHANGES_BATCH (if N > 1 and flag on) or N NEW_CHANGES messages. +// Re-implement the decision here so the test doesn't have to stand up +// the full pad/DB stack — and pin it against the actual implementation +// via a comment in PadMessageHandler. + +type Pending = {newRev: number; changeset: string; apool: unknown; + author: string; currentTime: number; timeDelta: number}; +type Emit = {type: 'COLLABROOM'; data: any}; + +const decideEmits = (pending: Pending[], batchEnabled: boolean): Emit[] => { + if (pending.length === 0) return []; + if (batchEnabled && pending.length > 1) { + return [{type: 'COLLABROOM', data: {type: 'NEW_CHANGES_BATCH', changes: pending}}]; + } + return pending.map((change) => ({ + type: 'COLLABROOM', + data: {type: 'NEW_CHANGES', ...change}, + })); +}; + +const fakePending = (n: number): Pending[] => + Array.from({length: n}, (_, i) => ({ + newRev: i + 1, changeset: `=${i}`, apool: {}, author: 'a.1', + currentTime: 1_000 * (i + 1), timeDelta: 1_000, + })); + +describe('NEW_CHANGES_BATCH emit decision', () => { + it('with flag OFF, sends one NEW_CHANGES per rev regardless of count', () => { + settings.newChangesBatch = false; + const emits = decideEmits(fakePending(5), settings.newChangesBatch); + expect(emits).toHaveLength(5); + expect(emits.every((e) => e.data.type === 'NEW_CHANGES')).toBe(true); + }); + + it('with flag ON and one queued rev, still sends NEW_CHANGES (no batch overhead)', () => { + settings.newChangesBatch = true; + const emits = decideEmits(fakePending(1), settings.newChangesBatch); + expect(emits).toHaveLength(1); + expect(emits[0]!.data.type).toBe('NEW_CHANGES'); + }); + + it('with flag ON and multiple queued revs, sends one NEW_CHANGES_BATCH', () => { + settings.newChangesBatch = true; + const emits = decideEmits(fakePending(5), settings.newChangesBatch); + expect(emits).toHaveLength(1); + expect(emits[0]!.data.type).toBe('NEW_CHANGES_BATCH'); + expect(emits[0]!.data.changes).toHaveLength(5); + expect(emits[0]!.data.changes[0]!.newRev).toBe(1); + expect(emits[0]!.data.changes[4]!.newRev).toBe(5); + }); + + it('empty pending list emits nothing', () => { + settings.newChangesBatch = true; + expect(decideEmits([], settings.newChangesBatch)).toEqual([]); + }); +});