[lit-html] Use a double-keyed LRU cache for server rendered static html #5118

jimsimon · 2025-10-10T18:05:53Z

This change switches static html to use a double keyed cache. The outer key is the pre-flattened template strings and the inner key is the final template string after all of the static parts have been merged into it (which was the previous behavior). It also implements the inner cache as a simple LRU with a relatively small max size. The idea here is that the ideal usage of static html has a small cardinality, but improper usage may have a high/infinite cardinality and we don't want to OOM the server (when using SSR) with an ever-growing cache.

changeset-bot · 2025-10-10T18:05:57Z

🦋 Changeset detected

Latest commit: 81dd1be

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
lit-html	Patch

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github-actions · 2025-10-10T18:06:07Z

📊 Tachometer Benchmark Results

Summary

nop-update

this-change, tip-of-tree, previous-release: unsure 🔍 -4% - +8% (-0.52ms - +1.05ms)
^{this-change vs tip-of-tree}

render

this-change: 45.65ms - 61.25ms
this-change, tip-of-tree, previous-release: unsure 🔍 -3% - +4% (-0.58ms - +0.74ms)
^{this-change vs tip-of-tree}
this-change, tip-of-tree, previous-release: unsure 🔍 -3% - +2% (-1.02ms - +0.64ms)
^{this-change vs tip-of-tree}
this-change, tip-of-tree, previous-release: unsure 🔍 -15% - +26% (-9.33ms - +16.91ms)
^{this-change vs tip-of-tree}

update

this-change: 445.70ms - 451.84ms
this-change, tip-of-tree, previous-release: unsure 🔍 -3% - +4% (-1.15ms - +1.61ms)
^{this-change vs tip-of-tree}
this-change, tip-of-tree, previous-release: unsure 🔍 -0% - +3% (-0.04ms - +2.21ms)
^{this-change vs tip-of-tree}
this-change, tip-of-tree, previous-release: unsure 🔍 -1% - +1% (-5.38ms - +3.52ms)
^{this-change vs tip-of-tree}

update-reflect

this-change: 428.36ms - 431.60ms
this-change, tip-of-tree, previous-release: unsure 🔍 -1% - +1% (-2.51ms - +6.60ms)
^{this-change vs tip-of-tree}

Results

this-change

Browser: chrome-headless 140.0.0.0
Sample size: 50
Built by: Benchmarks #7004
Commit: 81dd1be

render

Version	Avg time	vs
	45.65ms - 61.25ms	-

update

Version	Avg time	vs
	445.70ms - 451.84ms	-

update-reflect

Version	Avg time	vs
	428.36ms - 431.60ms	-

this-change, tip-of-tree, previous-release

Browser: chrome-headless 140.0.0.0
Sample size: 30
Built by: Benchmarks #7004
Commit: 81dd1be

render

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	18.03ms - 18.95ms	-	unsure 🔍 -3% - +4% -0.58ms - +0.74ms	unsure 🔍 -4% - +2% -0.81ms - +0.40ms
tip-of-tree tip-of-tree	17.93ms - 18.88ms	unsure 🔍 -4% - +3% -0.74ms - +0.58ms	-	unsure 🔍 -5% - +2% -0.90ms - +0.33ms
previous-release previous-release	18.30ms - 19.09ms	unsure 🔍 -2% - +4% -0.40ms - +0.81ms	unsure 🔍 -2% - +5% -0.33ms - +0.90ms	-

update

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	36.03ms - 37.87ms	-	unsure 🔍 -3% - +4% -1.15ms - +1.61ms	unsure 🔍 -3% - +3% -1.29ms - +1.15ms
tip-of-tree tip-of-tree	35.69ms - 37.74ms	unsure 🔍 -4% - +3% -1.61ms - +1.15ms	-	unsure 🔍 -4% - +3% -1.61ms - +0.99ms
previous-release previous-release	36.23ms - 37.82ms	unsure 🔍 -3% - +3% -1.15ms - +1.29ms	unsure 🔍 -3% - +4% -0.99ms - +1.61ms	-

nop-update

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	12.36ms - 13.52ms	-	unsure 🔍 -4% - +8% -0.52ms - +1.05ms	slower ❌ 0% - 13% 0.05ms - 1.52ms
tip-of-tree tip-of-tree	12.15ms - 13.19ms	unsure 🔍 -8% - +4% -1.05ms - +0.52ms	-	unsure 🔍 -1% - +10% -0.17ms - +1.21ms
previous-release previous-release	11.70ms - 12.60ms	faster ✔ 1% - 12% 0.05ms - 1.52ms	unsure 🔍 -9% - +1% -1.21ms - +0.17ms	-

this-change, tip-of-tree, previous-release

Browser: chrome-headless 140.0.0.0
Sample size: 50
Built by: Benchmarks #7004
Commit: 81dd1be

render

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	35.03ms - 36.11ms	-	unsure 🔍 -3% - +2% -1.02ms - +0.64ms	unsure 🔍 -3% - +2% -1.11ms - +0.76ms
tip-of-tree tip-of-tree	35.12ms - 36.40ms	unsure 🔍 -2% - +3% -0.64ms - +1.02ms	-	unsure 🔍 -3% - +3% -0.98ms - +1.01ms
previous-release previous-release	34.98ms - 36.51ms	unsure 🔍 -2% - +3% -0.76ms - +1.11ms	unsure 🔍 -3% - +3% -1.01ms - +0.98ms	-

update

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	80.19ms - 81.80ms	-	unsure 🔍 -0% - +3% -0.04ms - +2.21ms	slower ❌ 0% - 3% 0.06ms - 2.28ms
tip-of-tree tip-of-tree	79.12ms - 80.70ms	unsure 🔍 -3% - +0% -2.21ms - +0.04ms	-	unsure 🔍 -1% - +1% -1.02ms - +1.19ms
previous-release previous-release	79.06ms - 80.59ms	faster ✔ 0% - 3% 0.06ms - 2.28ms	unsure 🔍 -1% - +1% -1.19ms - +1.02ms	-

this-change, tip-of-tree, previous-release

Browser: chrome-headless 140.0.0.0
Sample size: 50
Built by: Benchmarks #7004
Commit: 81dd1be

render

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	61.24ms - 79.61ms	-	unsure 🔍 -15% - +26% -9.33ms - +16.91ms	unsure 🔍 -5% - +45% -1.45ms - +25.00ms
tip-of-tree tip-of-tree	57.27ms - 76.00ms	unsure 🔍 -24% - +13% -16.91ms - +9.33ms	-	unsure 🔍 -11% - +38% -5.37ms - +21.33ms
previous-release previous-release	49.14ms - 68.16ms	unsure 🔍 -34% - +1% -25.00ms - +1.45ms	unsure 🔍 -31% - +7% -21.33ms - +5.37ms	-

update

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	434.85ms - 441.05ms	-	unsure 🔍 -1% - +1% -5.38ms - +3.52ms	unsure 🔍 -1% - +0% -6.45ms - +1.99ms
tip-of-tree tip-of-tree	435.69ms - 442.07ms	unsure 🔍 -1% - +1% -3.52ms - +5.38ms	-	unsure 🔍 -1% - +1% -5.58ms - +2.98ms
previous-release previous-release	437.33ms - 443.03ms	unsure 🔍 -0% - +1% -1.99ms - +6.45ms	unsure 🔍 -1% - +1% -2.98ms - +5.58ms	-

update-reflect

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	441.84ms - 450.27ms	-	unsure 🔍 -1% - +1% -2.51ms - +6.60ms	unsure 🔍 -1% - +1% -3.09ms - +6.24ms
tip-of-tree tip-of-tree	442.29ms - 445.73ms	unsure 🔍 -1% - +1% -6.60ms - +2.51ms	-	unsure 🔍 -1% - +0% -3.10ms - +2.16ms
previous-release previous-release	442.49ms - 446.47ms	unsure 🔍 -1% - +1% -6.24ms - +3.09ms	unsure 🔍 -0% - +1% -2.16ms - +3.10ms	-

_{tachometer-reporter-action v2 for Benchmarks}

github-actions · 2025-10-10T18:07:34Z

The size of lit-html.js and lit-core.min.js are as expected.

jimsimon requested a review from justinfagnani October 10, 2025 18:06

[lit-ssr] Use double-keyed LRU cache for static html

4fd1dc2

jimsimon force-pushed the lru-static-cache branch from 382b730 to 4fd1dc2 Compare October 10, 2025 18:08

Add LRU cache to export map

9ed920c

jimsimon changed the title ~~[lit-ssr] Use double-keyed LRU cache for static html~~ [lit-ssr] Use a double-keyed LRU cache for static html Oct 10, 2025

Only use LRU cache for SSR

7f443ef

jimsimon mentioned this pull request Oct 10, 2025

[lit-html] Allow the template cache to be customized when using the withStatic() tag generator #5113

Draft

jimsimon added 3 commits October 10, 2025 16:20

Don't rely on Map type for static strings cache interface

a8e386d

Add some comments and rename some variables

cea99c6

Add changeset

81dd1be

jimsimon changed the title ~~[lit-ssr] Use a double-keyed LRU cache for static html~~ [lit-ssr] Use a double-keyed LRU cache for server rendered static html Oct 10, 2025

jimsimon marked this pull request as ready for review October 10, 2025 21:02

jimsimon requested a review from kevinpschaaf as a code owner October 10, 2025 21:02

jimsimon changed the title ~~[lit-ssr] Use a double-keyed LRU cache for server rendered static html~~ [lit-html] Use a double-keyed LRU cache for server rendered static html Oct 10, 2025

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