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docs: update throttling docs to public version #7332

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Feb 28, 2019
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docs: update throttling docs to public version #7332

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2 changes: 1 addition & 1 deletion docs/throttling.md
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Expand Up @@ -12,7 +12,7 @@ These exact figures are used as [Lighthouse's throttling default](https://github
## Throttling basics

1. Simulated throttling, which Lighthouse uses by default, is computed throttling _after a trace has been recorded_ which makes it very fast and deterministic. However, due to the imperfect nature of predicting alternate execution paths, there is inherent inaccuracy that is summarized in this doc: [Lighthouse Metric Variability and Accuracy](https://docs.google.com/document/d/1BqtL-nG53rxWOI5RO0pItSRPowZVnYJ_gBEQCJ5EeUE/edit). The TLDR: while it's roughly as accurate or better than DevTools throttling for most sites, it suffers from edge cases and a deep investigation to performance should use _Packet-level_ throttling tools.
1. The DevTools network throttling, which Lighthouse uses for `throttlingMethod='devtools'`, is implemented within Chrome at the _request-level_. As a result, it has some downsides that are now summarized in this doc: [Network Throttling & Chrome - status](https://docs.google.com/document/d/1TwWLaLAfnBfbk5_ZzpGXegPapCIfyzT4MWuZgspKUAQ/edit). The TLDR: while it's a [decent approximation](https://docs.google.com/document/d/1uS9SH1KpVH31JAmf-iIZ61VazwAF9MrCVwETshBC4UQ/edit), it's not a sufficient model of a slow connection. The [multipliers used in Lighthouse](https://github.com/GoogleChrome/lighthouse/blob/3be483287a530fb560c843b7299ef9cfe91ce1cc/lighthouse-core/lib/emulation.js#L33-L39) attempt to correct for the differences.
1. The DevTools network throttling, which Lighthouse uses for `throttlingMethod='devtools'`, is implemented within Chrome at the _request-level_. As a result, it has some downsides that are now summarized in this doc: [Network Throttling & Chrome - status](https://docs.google.com/document/d/1TwWLaLAfnBfbk5_ZzpGXegPapCIfyzT4MWuZgspKUAQ/edit). The TLDR: while it's a [decent approximation](https://docs.google.com/document/d/10lfVdS1iDWCRKQXPfbxEn4Or99D64mvNlugP1AQuFlE/edit), it's not a sufficient model of a slow connection. The [multipliers used in Lighthouse](https://github.com/GoogleChrome/lighthouse/blob/3be483287a530fb560c843b7299ef9cfe91ce1cc/lighthouse-core/lib/emulation.js#L33-L39) attempt to correct for the differences.
1. _Proxy-level_ throttling tools do not affect UDP data, so they're not recommended.
1. _Packet-level_ throttling tools are able to make the most accurate network simulation.

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3 changes: 2 additions & 1 deletion lighthouse-core/config/constants.js
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Expand Up @@ -8,7 +8,8 @@
/**
* Adjustments needed for DevTools network throttling to simulate
* more realistic network conditions.
* See: crbug.com/721112
* @see https://crbug.com/721112
* @see https://docs.google.com/document/d/10lfVdS1iDWCRKQXPfbxEn4Or99D64mvNlugP1AQuFlE/edit
*/
const DEVTOOLS_RTT_ADJUSTMENT_FACTOR = 3.75;
const DEVTOOLS_THROUGHPUT_ADJUSTMENT_FACTOR = 0.9;
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