Add configuration for ISR Memory Cache Size (#21535)

[stefanb2]

This allows the user to adjust the LRU cache size according to the
application need:

• optimize the cache size based on average page HTML & JSON size
• disable the memory cache by setting the size to 0

The hard-coded default of 50MB has been moved from the code to the
default configuration object.

Fixes #21535
See also #27325

Bug

• Related issues linked using fixes #number
• Integration tests added
• Errors have helpful link attached, see contributing.md

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• Integration tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.
• Errors have helpful link attached, see contributing.md

Documentation / Examples

• Make sure the linting passes

[stefanb2]

I'm pretty sure this is still inadequate:

• config validation missing (must be integer, must be greater or equal to 0)
• integration test

I'm open to suggestions how to improve the PR.

[stefanb2]

Hmm, maybe it wasn't such a good idea to reference a question PR...

[ijjk]

Hi, I think we would want to start with making this an experimental config like isrMemoryCacheSize similar to the flush to disk option here (which needs renaming to isrFlush) and if we're starting with it experimental it does not need to be documented initially

[balazsorban44]

After some research on a memory leak at work, we suspect the problem was/is with the current LRU cache. The issue was quickly turned into a discussion, but after taking some memory heap dumps, we still suspect it originated from Next.js. Somehow the LRU cache grew over the allowed 50 MB.

See #26801

It would be interesting to see if our issue resolves by completely disabling it. 👀

[stefanb2]

@ijjk thanks for the guidance. I incorporated your suggestions in the latest change set.
@balazsorban44 in the latest change set a size of 0 will disable the memory cache, but keep the disk cache and revalidation check.

[ijjk]

Thanks for the PR!

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	stefanb2/next.js topic-pr-21535	Change
buildDuration	16.5s	16.7s	⚠️ +136ms
buildDurationCached	3.7s	3.6s	-118ms
nodeModulesSize	49.5 MB	49.5 MB	⚠️ +762 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	stefanb2/next.js topic-pr-21535	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.916	3.085	⚠️ +0.17
/ avg req/sec	857.3	810.4	⚠️ -46.9
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.802	1.749	-0.05
/error-in-render avg req/sec	1387.56	1429.54	+41.98

Client Bundles (main, webpack, commons)

	vercel/next.js canary	stefanb2/next.js topic-pr-21535	Change
359.HASH.js gzip	2.96 kB	2.96 kB	✓
745.HASH.js gzip	180 B	180 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	21 kB	21 kB	✓
webpack-HASH.js gzip	1.53 kB	1.53 kB	✓
Overall change	67.9 kB	67.9 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	stefanb2/next.js topic-pr-21535	Change
polyfills-HASH.js gzip	31.1 kB	31.1 kB	✓
Overall change	31.1 kB	31.1 kB	✓

Client Pages

	vercel/next.js canary	stefanb2/next.js topic-pr-21535	Change
_app-HASH.js gzip	803 B	803 B	✓
_error-HASH.js gzip	3.06 kB	3.06 kB	✓
amp-HASH.js gzip	554 B	554 B	✓
css-HASH.js gzip	329 B	329 B	✓
dynamic-HASH.js gzip	2.52 kB	2.52 kB	✓
head-HASH.js gzip	2.28 kB	2.28 kB	✓
hooks-HASH.js gzip	903 B	903 B	✓
image-HASH.js gzip	5.61 kB	5.61 kB	✓
index-HASH.js gzip	261 B	261 B	✓
link-HASH.js gzip	1.66 kB	1.66 kB	✓
routerDirect..HASH.js gzip	319 B	319 B	✓
script-HASH.js gzip	387 B	387 B	✓
withRouter-HASH.js gzip	320 B	320 B	✓
bb14e60e810b..30f.css gzip	125 B	125 B	✓
Overall change	19.1 kB	19.1 kB	✓

Client Build Manifests

	vercel/next.js canary	stefanb2/next.js topic-pr-21535	Change
_buildManifest.js gzip	490 B	490 B	✓
Overall change	490 B	490 B	✓

Rendered Page Sizes

	vercel/next.js canary	stefanb2/next.js topic-pr-21535	Change
index.html gzip	530 B	530 B	✓
link.html gzip	542 B	542 B	✓
withRouter.html gzip	525 B	525 B	✓
Overall change	1.6 kB	1.6 kB	✓

---

Webpack 4 Mode (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	stefanb2/next.js topic-pr-21535	Change
buildDuration	13s	12.7s	-318ms
buildDurationCached	5s	4.9s	-76ms
nodeModulesSize	49.5 MB	49.5 MB	⚠️ +762 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	stefanb2/next.js topic-pr-21535	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.87	2.796	-0.07
/ avg req/sec	871.21	894.04	+22.83
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.864	1.84	-0.02
/error-in-render avg req/sec	1341.23	1358.43	+17.2

Client Bundles (main, webpack, commons)

	vercel/next.js canary	stefanb2/next.js topic-pr-21535	Change
17.HASH.js gzip	2.98 kB	2.98 kB	✓
18.HASH.js gzip	185 B	185 B	✓
677f882d2ed8..HASH.js gzip	13.7 kB	13.7 kB	✓
framework.HASH.js gzip	41.9 kB	41.9 kB	✓
main-HASH.js gzip	8.4 kB	8.4 kB	✓
webpack-HASH.js gzip	1.22 kB	1.22 kB	✓
Overall change	68.5 kB	68.5 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	stefanb2/next.js topic-pr-21535	Change
polyfills-HASH.js gzip	31.3 kB	31.3 kB	✓
Overall change	31.3 kB	31.3 kB	✓

Client Pages

	vercel/next.js canary	stefanb2/next.js topic-pr-21535	Change
_app-HASH.js gzip	791 B	791 B	✓
_error-HASH.js gzip	3.76 kB	3.76 kB	✓
amp-HASH.js gzip	552 B	552 B	✓
css-HASH.js gzip	333 B	333 B	✓
dynamic-HASH.js gzip	2.71 kB	2.71 kB	✓
head-HASH.js gzip	2.97 kB	2.97 kB	✓
hooks-HASH.js gzip	911 B	911 B	✓
index-HASH.js gzip	231 B	231 B	✓
link-HASH.js gzip	1.64 kB	1.64 kB	✓
routerDirect..HASH.js gzip	298 B	298 B	✓
script-HASH.js gzip	3.02 kB	3.02 kB	✓
withRouter-HASH.js gzip	294 B	294 B	✓
e025d2764813..52f.css gzip	125 B	125 B	✓
Overall change	17.6 kB	17.6 kB	✓

Client Build Manifests

	vercel/next.js canary	stefanb2/next.js topic-pr-21535	Change
_buildManifest.js gzip	500 B	500 B	✓
Overall change	500 B	500 B	✓

Rendered Page Sizes

	vercel/next.js canary	stefanb2/next.js topic-pr-21535	Change
index.html gzip	576 B	576 B	✓
link.html gzip	587 B	587 B	✓
withRouter.html gzip	568 B	568 B	✓
Overall change	1.73 kB	1.73 kB	✓

Commit: 926198e