Improve SSR hydration performance #6204
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- Fixes #4308 by avoiding de- and reattaching nodes during hydration - Turns existing append, insert and detach methods into "upserts" The new "hydration mode" was added in order to maintain the detach by default behavior during hydration. By tracking which nodes are claimed during hydration unclaimed nodes can then removed from the DOM at the end of hydration without touching the remaining nodes.
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Thank you @benmccann and @jonatansberg ! |
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This PR creates a weird issue where Maybe also links to this issue: #1067 Update : This one includes reproduction: https://github.com/sveltejs/kit/issues/1288 |
tanhauhau
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Conduitry
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May 3, 2021
This reverts commit 10e3e3d.
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Jun 9, 2021
Unreverts the hydration optimisation from sveltejs#6204 and fixes the `claim_text` issue as described in sveltejs#6279 (comment)
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Closes #5623. This is that PR rebased with logging removed. Thanks to @jonatansberg for paving the way on this!
Also closes #4309
Background
This PR improves SSR hydration performance through minimizing DOM mutations during hydration by avoiding de- and reattaching nodes during hydration. This should fix #1067, fix #4308, fix #5108, and fix #4975.
In order for this to work I added a new new "hydration mode". This way it's possible to maintain the detach by default behavior during hydration without modifying the generated component output. There might be better ways to do this if we reconsider fragment creation (as suggested in #3898 and #4219) but that would be a significant undertaking.
The existing append, insert and detached methods have been modified to track which nodes are claimed during hydration. That way unclaimed nodes can then removed from the DOM at the end of hydration without touching the remaining nodes.
In order for this to work the append, insert and detach methods have also been made idempotent (i.e. "upserts") in order to allow attaching an already attached DOM node.
Results
Initial local benchmarks against johnells.se (which runs on Sapper) shows a 50% reduction of LCP when running Lighthouse, which results in decent PageSpeed score improvement.
Production benchmarks on the SvelteKit app at https://c3.ventures/ show a PageSpeed score improvement from 92 to 99.