Track new front-end metric: LCP-TTFB #48288
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Median is stable enough, we can stick to it.
oandregal
added
[Type] Build Tooling
oandregal
commented
Feb 21, 2023
bin/plugin/commands/performance.js
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| largestContentfulPaintP75: percentile75( | ||
| results.largestContentfulPaint | ||
| ), | ||
| timeToFirstByte, |
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This is the gist, the rest are docs changes:
- rename
timeToFirstByteMediantotimeToFirstByte - remove
timeToFirstByteP75 - rename
largestContentfulPaintMediantolargestContentfulPaint - remove
largestContentfulPaintP75 - add
lcMinusTtfb
I presume this is going to need to codevitals.run config changes to gather the existing metrics we report for the updated fields. If renaming is problematic for codevitals, I can revert that and leave the *Median fields while still removing the *P75 ones.
Can we also should the new one lcpMinetTtfb as LCP - TTFB (classic or block), @youknowriad ?
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Size Change: +295 B (0%) Total Size: 1.33 MB
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Flaky tests detected in 9309f15. 🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/4241199921
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youknowriad
reviewed
Feb 22, 2023
bin/plugin/commands/performance.js
Outdated
| ), | ||
| timeToFirstByte, | ||
| largestContentfulPaint, | ||
| lcpMinusTtfb: largestContentfulPaint - timeToFirstByte, |
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I see this is only computed here, meaning it won't be part of the logged results when you run the tests manually using npm run test:performance ... should we make the computation in the spec files directly instead and add a log to the performance logger as well?
youknowriad
approved these changes
Feb 22, 2023
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What?
This PR does two things:
Why?
The median has proven stable enough, so we don't need the percentile as well. We are only shipping the median to
codevitals.runanyway.The TTFB represents a big chunk of the LCP time (50% for classic, 80% for block themes). It influences LCP so much that we are unable to actually detect changes that affect the time it takes the client to render a page.
How?
By subtracting TTFB (median) from LCP.
Testing Instructions
Verify that the front-end metrics include LCP, TTFB, and LCP-TTFB.