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Change cursors batch time formula on presence update #333

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Sep 18, 2024
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Change cursors batch time formula on presence update #333

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4 changes: 2 additions & 2 deletions src/Cursors.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -116,7 +116,7 @@ describe('Cursors', () => {
vi.spyOn(channel.presence, 'get').mockImplementation(createPresenceCount(2));
await cursors['onPresenceUpdate']();
expect(batching.shouldSend).toBeTruthy();
expect(batching.batchTime).toEqual(50);
expect(batching.batchTime).toEqual(25);
});

it<CursorsTestContext>('batchTime is updated when multiple people are present', async ({
Expand All @@ -126,7 +126,7 @@ describe('Cursors', () => {
}) => {
vi.spyOn(channel.presence, 'get').mockImplementation(createPresenceCount(2));
await cursors['onPresenceUpdate']();
expect(batching.batchTime).toEqual(50);
expect(batching.batchTime).toEqual(25);
});

describe('pushCursorPosition', () => {
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6 changes: 5 additions & 1 deletion src/Cursors.ts
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Expand Up @@ -105,7 +105,11 @@ export default class Cursors extends EventEmitter<CursorsEventMap> {
const channel = this.getChannel();
const cursorsMembers = await channel.presence.get();
this.cursorBatching.setShouldSend(cursorsMembers.length > 1);
this.cursorBatching.setBatchTime(cursorsMembers.length * this.options.outboundBatchInterval);
/**
* Since server-side batching is automically enabled for cursors channels, we can now adjust the client-side batching interval more granularly.
* E.g. multiply the configured outboundBatchInterval by groups of 100 members instead of the total number of members.
*/
this.cursorBatching.setBatchTime(Math.ceil(cursorsMembers.length / 100) * this.options.outboundBatchInterval);
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It's hard to understand why this is divided by 100 now?

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Before we were adjusting with cursorsMembers.length * this.options.outboundBatchInterval, which made the client-side latency climb linearly with the presence set. Since we have server-side batching now we don't need to make it so steep client-side. Therefore, the ticket suggestion was that it could climb with groups of 100s, which makes client-side batching latency grow much slower.

Example assuming outboundBatchInterval=25ms:

  • if #presenceMembers <= 100: batchTime=25ms
  • if #presenceMembers <= 200: batchTime=50ms
  • if #presenceMembers <= 300: batchTime=75ms

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Ok thanks, makes sense, perhaps put that as a comment in the code?

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Added as a comment in the code

}

private isUnsubscribed() {
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