[Fizz] Track postponed holes in the prerender pass #27317

sebmarkbage · 2023-08-30T18:23:12Z

This is basically the implementation for the prerender pass.

Instead of forking basically the whole implementation for prerender, I just add a conditional field on the request. If it's null it behaves like before. If it's non-null then instead of triggering client rendered boundaries it triggers those into a "postponed" state which is basically just a variant of "pending". It's supposed to be filled in later.

It also builds up a serializable tree of which path can be followed to find the holes. This is basically a reverse KeyPath tree.

It is unfortunate that this approach adds more code to the regular Fizz builds but in practice. It seems like this side is not going to add much code and we might instead just want to merge the builds so that it's smaller when you have prerender and resume in the same bundle - which I think will be common in practice.

This just implements the prerender side, and not the resume side, which is why the tests have a TODO. That's in a follow up PR.

react-sizebot · 2023-08-30T21:41:06Z

Comparing: 3808b01...7733a15

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	165.63 kB	165.63 kB	=	51.88 kB	51.88 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	174.70 kB	174.70 kB	=	54.61 kB	54.61 kB
facebook-www/ReactDOM-prod.classic.js	=	570.44 kB	570.44 kB	=	100.45 kB	100.45 kB
facebook-www/ReactDOM-prod.modern.js	=	554.21 kB	554.21 kB	=	97.61 kB	97.61 kB
oss-experimental/react-dom/server.node.js	+6.93%	0.69 kB	0.74 kB	+1.12%	0.27 kB	0.27 kB
oss-stable-semver/react-dom/server.node.js	+6.93%	0.69 kB	0.74 kB	+1.12%	0.27 kB	0.27 kB
oss-stable/react-dom/server.node.js	+6.93%	0.69 kB	0.74 kB	+1.12%	0.27 kB	0.27 kB
oss-experimental/react-server/cjs/react-server.production.min.js	+6.16%	26.36 kB	27.99 kB	+4.68%	8.96 kB	9.38 kB
oss-experimental/react-server/cjs/react-server.development.js	+3.95%	154.42 kB	160.52 kB	+3.21%	38.71 kB	39.95 kB
oss-experimental/react-dom/cjs/react-dom-static.node.production.min.js	+2.34%	69.76 kB	71.39 kB	+1.91%	21.81 kB	22.22 kB
oss-experimental/react-dom/cjs/react-dom-static.browser.production.min.js	+2.29%	65.23 kB	66.73 kB	+1.95%	20.25 kB	20.64 kB
oss-experimental/react-dom/cjs/react-dom-static.edge.production.min.js	+2.28%	65.56 kB	67.05 kB	+1.89%	20.38 kB	20.76 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-experimental/react-dom/server.node.js	+6.93%	0.69 kB	0.74 kB	+1.12%	0.27 kB	0.27 kB
oss-stable-semver/react-dom/server.node.js	+6.93%	0.69 kB	0.74 kB	+1.12%	0.27 kB	0.27 kB
oss-stable/react-dom/server.node.js	+6.93%	0.69 kB	0.74 kB	+1.12%	0.27 kB	0.27 kB
oss-experimental/react-server/cjs/react-server.production.min.js	+6.16%	26.36 kB	27.99 kB	+4.68%	8.96 kB	9.38 kB
oss-experimental/react-server/cjs/react-server.development.js	+3.95%	154.42 kB	160.52 kB	+3.21%	38.71 kB	39.95 kB
oss-experimental/react-dom/cjs/react-dom-static.node.production.min.js	+2.34%	69.76 kB	71.39 kB	+1.91%	21.81 kB	22.22 kB
oss-experimental/react-dom/cjs/react-dom-static.browser.production.min.js	+2.29%	65.23 kB	66.73 kB	+1.95%	20.25 kB	20.64 kB
oss-experimental/react-dom/cjs/react-dom-static.edge.production.min.js	+2.28%	65.56 kB	67.05 kB	+1.89%	20.38 kB	20.76 kB
oss-experimental/react-dom/cjs/react-dom-server.bun.production.min.js	+1.94%	68.36 kB	69.69 kB	+1.55%	20.99 kB	21.32 kB
oss-experimental/react-dom/cjs/react-dom-server-legacy.node.production.min.js	+1.90%	69.94 kB	71.27 kB	+1.55%	21.27 kB	21.60 kB
oss-experimental/react-dom/cjs/react-dom-server.edge.production.min.js	+1.89%	70.33 kB	71.66 kB	+1.55%	21.87 kB	22.21 kB
oss-experimental/react-dom/cjs/react-dom-server.node.production.min.js	+1.89%	70.48 kB	71.81 kB	+1.65%	21.95 kB	22.31 kB
oss-experimental/react-dom/cjs/react-dom-server-legacy.browser.production.min.js	+1.83%	64.95 kB	66.14 kB	+1.62%	19.62 kB	19.94 kB
oss-experimental/react-dom/umd/react-dom-server-legacy.browser.production.min.js	+1.82%	65.11 kB	66.30 kB	+1.61%	20.01 kB	20.33 kB
oss-experimental/react-dom/cjs/react-dom-server.browser.production.min.js	+1.80%	66.03 kB	67.22 kB	+1.61%	20.38 kB	20.71 kB
oss-experimental/react-dom/umd/react-dom-server.browser.production.min.js	+1.80%	66.17 kB	67.36 kB	+1.49%	20.65 kB	20.96 kB
oss-experimental/react-dom/cjs/react-dom-static.browser.development.js	+1.69%	358.23 kB	364.30 kB	+1.54%	80.61 kB	81.86 kB
oss-experimental/react-dom/cjs/react-dom-static.edge.development.js	+1.69%	358.64 kB	364.71 kB	+1.53%	80.74 kB	81.98 kB
oss-experimental/react-dom/cjs/react-dom-static.node.development.js	+1.68%	360.38 kB	366.44 kB	+1.54%	80.93 kB	82.18 kB
oss-stable-semver/react-server/cjs/react-server.production.min.js	+1.54%	25.52 kB	25.91 kB	+1.25%	8.67 kB	8.78 kB
oss-stable/react-server/cjs/react-server.production.min.js	+1.54%	25.52 kB	25.91 kB	+1.25%	8.67 kB	8.78 kB
oss-experimental/react-dom/cjs/react-dom-server.bun.development.js	+1.54%	356.59 kB	362.08 kB	+1.40%	80.06 kB	81.19 kB
oss-experimental/react-dom/cjs/react-dom-server-legacy.browser.development.js	+1.53%	359.15 kB	364.63 kB	+1.39%	80.55 kB	81.67 kB
oss-experimental/react-dom/cjs/react-dom-server.browser.development.js	+1.52%	360.77 kB	366.25 kB	+1.39%	80.83 kB	81.95 kB
oss-experimental/react-dom/cjs/react-dom-server-legacy.node.development.js	+1.52%	361.06 kB	366.54 kB	+1.38%	81.01 kB	82.12 kB
oss-experimental/react-dom/cjs/react-dom-server.edge.development.js	+1.52%	361.18 kB	366.66 kB	+1.39%	80.96 kB	82.08 kB
oss-experimental/react-dom/cjs/react-dom-server.node.development.js	+1.52%	361.70 kB	367.19 kB	+1.38%	80.88 kB	82.00 kB
oss-experimental/react-dom/umd/react-dom-server-legacy.browser.development.js	+1.51%	376.33 kB	382.03 kB	+1.38%	81.38 kB	82.50 kB
oss-experimental/react-dom/umd/react-dom-server.browser.development.js	+1.51%	378.04 kB	383.74 kB	+1.38%	81.69 kB	82.82 kB
oss-stable-semver/react-server/cjs/react-server.development.js	+0.77%	148.43 kB	149.57 kB	+0.75%	36.97 kB	37.25 kB
oss-stable/react-server/cjs/react-server.development.js	+0.77%	148.43 kB	149.57 kB	+0.75%	36.97 kB	37.25 kB
oss-experimental/react-noop-renderer/cjs/react-noop-renderer-flight-server.production.min.js	+0.23%	1.30 kB	1.31 kB	+0.33%	0.62 kB	0.62 kB
oss-stable-semver/react-noop-renderer/cjs/react-noop-renderer-flight-server.production.min.js	+0.23%	1.30 kB	1.31 kB	+0.33%	0.62 kB	0.62 kB
oss-stable/react-noop-renderer/cjs/react-noop-renderer-flight-server.production.min.js	+0.23%	1.30 kB	1.31 kB	+0.33%	0.62 kB	0.62 kB

Generated by 🚫 dangerJS against 7733a15

gnoff · 2023-08-30T22:38:51Z

packages/react-dom/src/__tests__/ReactDOMFizzServer-test.js

+ const b = new Stream.PassThrough();
+ b.setEncoding('utf8');
+ b.on('data', chunk => {
+ writable.write(chunk);
+ });
+
+ await act(() => {
+ resumed.pipe(writable);
+ });


did you mean to pipe to b or is the passthrough not necessary?

I intentionally do this so that it still closes the writable at the end. The purpose of b is to just exclude the close().

I renamed startWork to startRender and added a startPrerender. Later, we'll probably add a startResume. This just adds a non-null Map. This is a signal to the runtime to track postponed holes. Ideally this would be static but it's not worth the forking that would require. Especially since this is just a cost when you postpone other than a bit extra code.

Todo this we need to stash the rootFormatContext on the request. It's unfortunate that this is state that's not needed for regular rendering.

This is unfortunate that we need to add this to the render path in general but this doesn't really cost anything extra in terms of allocations since this object would live anyway so it's an extra field.

For now this only tracks inside boundaries but it's set up to handle holes in the root too. We now need a status field on the boundary because pendingTasks === 0 no longer implies that a boundary is complete.

This creates a tree that we can follow when replaying to find those holes. This flips the tree and encodes the ids at this point.

Because we don't flush the stream until later after we've returned we need to assign these points an ID early so that we can write them in the resume payload.

Since we're now assigning IDs eagerly to postponed boundaries and segments we can encode them into their serialized form eagerly. Instead of doing a second pass at the end.

This is basically the implementation for the prerender pass. Instead of forking basically the whole implementation for prerender, I just add a conditional field on the request. If it's `null` it behaves like before. If it's non-`null` then instead of triggering client rendered boundaries it triggers those into a "postponed" state which is basically just a variant of "pending". It's supposed to be filled in later. It also builds up a serializable tree of which path can be followed to find the holes. This is basically a reverse `KeyPath` tree. It is unfortunate that this approach adds more code to the regular Fizz builds but in practice. It seems like this side is not going to add much code and we might instead just want to merge the builds so that it's smaller when you have `prerender` and `resume` in the same bundle - which I think will be common in practice. This just implements the prerender side, and not the resume side, which is why the tests have a TODO. That's in a follow up PR. DiffTrain build for [b70a0d7](b70a0d7)

This is basically the implementation for the prerender pass. Instead of forking basically the whole implementation for prerender, I just add a conditional field on the request. If it's `null` it behaves like before. If it's non-`null` then instead of triggering client rendered boundaries it triggers those into a "postponed" state which is basically just a variant of "pending". It's supposed to be filled in later. It also builds up a serializable tree of which path can be followed to find the holes. This is basically a reverse `KeyPath` tree. It is unfortunate that this approach adds more code to the regular Fizz builds but in practice. It seems like this side is not going to add much code and we might instead just want to merge the builds so that it's smaller when you have `prerender` and `resume` in the same bundle - which I think will be common in practice. This just implements the prerender side, and not the resume side, which is why the tests have a TODO. That's in a follow up PR.

This is basically the implementation for the prerender pass. Instead of forking basically the whole implementation for prerender, I just add a conditional field on the request. If it's `null` it behaves like before. If it's non-`null` then instead of triggering client rendered boundaries it triggers those into a "postponed" state which is basically just a variant of "pending". It's supposed to be filled in later. It also builds up a serializable tree of which path can be followed to find the holes. This is basically a reverse `KeyPath` tree. It is unfortunate that this approach adds more code to the regular Fizz builds but in practice. It seems like this side is not going to add much code and we might instead just want to merge the builds so that it's smaller when you have `prerender` and `resume` in the same bundle - which I think will be common in practice. This just implements the prerender side, and not the resume side, which is why the tests have a TODO. That's in a follow up PR. DiffTrain build for commit b70a0d7.

sebmarkbage requested review from gnoff and acdlite August 30, 2023 18:23

facebook-github-bot added CLA Signed React Core Team Opened by a member of the React Core Team labels Aug 30, 2023

gnoff approved these changes Aug 30, 2023

View reviewed changes

sebmarkbage added 9 commits August 31, 2023 11:27

Fix Node Server export names

57488c6

Return postponed state when some postponed were tracked

9286b09

Todo this we need to stash the rootFormatContext on the request. It's unfortunate that this is state that's not needed for regular rendering.

Add basic tests

5e4869f

Track the key path on the SuspenseBoundary

d58d26d

This is unfortunate that we need to add this to the render path in general but this doesn't really cost anything extra in terms of allocations since this object would live anyway so it's an extra field.

Track postponed holes

3f0874a

For now this only tracks inside boundaries but it's set up to handle holes in the root too. We now need a status field on the boundary because pendingTasks === 0 no longer implies that a boundary is complete.

Encode postponed holes into a resumable path tree

e8c8152

This creates a tree that we can follow when replaying to find those holes. This flips the tree and encodes the ids at this point.

Eagerly assign ids to postponed segments or boundaries

e96bb09

Because we don't flush the stream until later after we've returned we need to assign these points an ID early so that we can write them in the resume payload.

Eagerly encode the serializable nodes

019dd90

Since we're now assigning IDs eagerly to postponed boundaries and segments we can encode them into their serialized form eagerly. Instead of doing a second pass at the end.

sebmarkbage force-pushed the prerendering branch from 03330f7 to 1aa8af6 Compare August 31, 2023 15:27

Gate test

7733a15

sebmarkbage force-pushed the prerendering branch from 1aa8af6 to 7733a15 Compare August 31, 2023 16:05

sebmarkbage merged commit b70a0d7 into facebook:main Aug 31, 2023
36 checks passed

acdlite mentioned this pull request Sep 14, 2023

Update React from dd480ef92 to d6dcad6a8. vercel/next.js#55399

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[Fizz] Track postponed holes in the prerender pass #27317

[Fizz] Track postponed holes in the prerender pass #27317

sebmarkbage commented Aug 30, 2023 •

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react-sizebot commented Aug 30, 2023 •

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gnoff Aug 30, 2023

sebmarkbage Aug 31, 2023

[Fizz] Track postponed holes in the prerender pass #27317

[Fizz] Track postponed holes in the prerender pass #27317

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sebmarkbage commented Aug 30, 2023 •

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