Improved url-utils performance for sitemap-scale workloads by acburdine · Pull Request #1095 · TryGhost/SDK

acburdine · 2026-10-02T15:31:43Z

Summary

Profiling Ghost's sitemap build on a 300k-post site showed url-utils at ~9% of busy CPU and ~1GB of allocation churn per cold build. The sitemap calls replacePermalink, createUrl and transformReadyToAbsolute (twice) for every post. This PR speeds up each of those.

Opt-in freeze()

Adds freeze(), unfreeze(), isFrozen and a frozen constructor option. Freezing snapshots getSiteUrl, getSubdir and getAdminUrl. Ghost's getSubdir runs new URL(config.get('url')) on every call, so freezing is the main win for createUrl. Unfrozen behaviour is unchanged.
Adds parseRootUrl, a cache of parsed root and CDN URLs, and caches the regex in deduplicateSubdirectory. Both depend only on their input string, so they can't go stale.
All caches in this PR share a small memoize helper backed by lru-cache (new dependency, already used by Ghost), capped at 100 entries each.
There is no createUrl result cache. With frozen getters createUrl takes about 0.1–0.2µs per call. A cache was ~2× slower on unique paths like the sitemap's.

transformReadyToAbsolute

UrlUtils#transformReadyToAbsolute now returns before computing the site URL or options when the string has no __GHOST_URL__. It builds the merged asset defaults once instead of on every call, and only merges options when the caller passes some.
The util uses an indexOf loop instead of a RegExp with a callback. It checks asset prefixes in place without slicing, and memoizes trailing-slash stripping of base URLs. The priority order is unchanged: media, then files, then image, then root.

replacePermalink

Dates are only computed when :year, :month or :day appears, so /:slug/ no longer creates a moment for each post.
Each permalink pattern is parsed once into literal and token parts (bounded cache) instead of running the token regex and a replace callback on every call. /:slug/ drops from 32ms to 4ms per 300k posts.
Dates and timestamps use a cached Intl.DateTimeFormat('en-CA') per timezone. Ghost passes published_at as a Date.
All other inputs still go through moment-timezone: strings (moment parses those without an offset as wall time in the site timezone), invalid dates, years outside 1900–9999, and timezones Intl rejects. So moment-timezone stays a dependency, used only as that fallback. Removing it would change output for those inputs.

Compatibility

Nothing under lib/utils is renamed or moved, and no exported helper's signature changes. The only addition is a parseRootUrl export.
Equivalence tests compare the new code with verbatim copies of the 5.3.0 implementations (test/utils/legacy/). The source is unchanged between 5.3.0 and 5.3.1.
- transformReadyToAbsolute, both the util and the UrlUtils method, frozen and unfrozen. Inputs include null/undefined/'', strings with no placeholder, lookalike prefixes, files/media/image prefixes, multiple and back-to-back placeholders, per-call overrides, custom static prefixes, an empty replacementStr, and with and without each CDN base URL.
- replacePermalink across /:slug/, date, :id, tag/author fallbacks and unknown tokens. Inputs include Date, number and string published_at values, a missing published_at (fake timers), and date-line, DST and skipped-day edges in UTC, Europe/Berlin, America/Los_Angeles, Pacific/Kiritimati, Pacific/Apia and others.
- A separate sweep (not committed) checked the date output over every Intl timezone (423) for dates in every year from 1900 to 2100: 2.55M cases, 0 mismatches.

Benchmark

300k synthetic posts. Per post: replacePermalink('/:slug/') + createUrl(path, false, true) + 2× transformReadyToAbsolute (post URL and feature image). getSubdir parses the URL on each call, as Ghost's does. Each variant runs in a fresh process; numbers are the median of 5 runs.

Node v22.23.3.

Variant	per-post url-utils work	transformReadyToAbsolute ×2 only
5.3.0	686ms	380ms
new, unfrozen	137ms	26ms
new, frozen	91ms	26ms
5.3.0, imageBaseUrl	688ms	387ms
new, unfrozen, imageBaseUrl	149ms	35ms
new, frozen, imageBaseUrl	104ms	37ms

Benchmark script (not shipped)

// Benchmarks the per-post url-utils work done by Ghost's sitemap build.
// Usage: node bench.js <path to new url-utils package>
// Compares published @tryghost/url-utils@5.3.0 (installed as url-utils-530)
// against the local build. Each variant runs in a fresh child process.
const {execFileSync} = require('child_process');
const path = require('path');

const POSTS = 300000;
const RUNS = 5;

function runVariant({pkg, frozen, imageBaseUrl}) {
    const UrlUtils = require(path.join(pkg, 'lib/UrlUtils')).default;
    const config = {url: 'https://example.com/'};

    const urlUtils = new UrlUtils({
        // mirrors Ghost, getSubdir parses the configured url on every call
        getSiteUrl: () => config.url,
        getSubdir: () => new URL(config.url).pathname.replace(/\/$/, ''),
        getAdminUrl: () => 'https://admin.example.com/',
        assetBaseUrls: imageBaseUrl ? {image: 'https://cdn.example.com/'} : {}
    });

    if (frozen) {
        urlUtils.freeze();
    }

    const posts = [];
    for (let i = 0; i < POSTS; i++) {
        posts.push({
            id: `5ca5b2b8a7f5e6001e${String(i).padStart(6, '0')}`,
            slug: `post-number-${i}`,
            published_at: new Date(Date.UTC(2020, 0, 1) + i * 60000),
            url: `__GHOST_URL__/post-number-${i}/`,
            feature_image: `__GHOST_URL__/content/images/2020/01/post-${i}.jpg`
        });
    }

    let sink = 0;
    const t0 = process.hrtime.bigint();
    for (const post of posts) {
        const urlPath = urlUtils.replacePermalink('/:slug/', post, 'UTC');
        sink += urlUtils.createUrl(urlPath, false, true).length;
        sink += urlUtils.transformReadyToAbsolute(post.url).length;
        sink += urlUtils.transformReadyToAbsolute(post.feature_image).length;
    }
    const t1 = process.hrtime.bigint();
    for (const post of posts) {
        sink += urlUtils.transformReadyToAbsolute(post.url).length;
        sink += urlUtils.transformReadyToAbsolute(post.feature_image).length;
    }
    const t2 = process.hrtime.bigint();

    if (sink === 0) {
        throw new Error('unexpected');
    }

    return {total: Number(t1 - t0) / 1e6, tra: Number(t2 - t1) / 1e6};
}

function median(values) {
    const sorted = [...values].sort((a, b) => a - b);
    return sorted[Math.floor(sorted.length / 2)];
}

if (process.argv[2] === '--child') {
    process.stdout.write(JSON.stringify(runVariant(JSON.parse(process.argv[3]))));
} else {
    const newPkg = path.resolve(process.argv[2]);
    const oldPkg = path.dirname(require.resolve('url-utils-530/package.json'));
    const variants = [];

    for (const imageBaseUrl of [false, true]) {
        variants.push({name: `5.3.0${imageBaseUrl ? ', imageBaseUrl' : ''}`, pkg: oldPkg, frozen: false, imageBaseUrl});
        variants.push({name: `new, unfrozen${imageBaseUrl ? ', imageBaseUrl' : ''}`, pkg: newPkg, frozen: false, imageBaseUrl});
        variants.push({name: `new, frozen${imageBaseUrl ? ', imageBaseUrl' : ''}`, pkg: newPkg, frozen: true, imageBaseUrl});
    }

    console.log(`node ${process.version}, ${POSTS} posts, median of ${RUNS} runs\n`);
    console.log('| Variant | per-post url-utils work | transformReadyToAbsolute ×2 only |');
    console.log('|---|---:|---:|');
    for (const variant of variants) {
        const results = [];
        for (let i = 0; i < RUNS; i++) {
            results.push(JSON.parse(execFileSync(process.execPath, [__filename, '--child', JSON.stringify(variant)], {encoding: 'utf8'})));
        }
        const total = median(results.map(r => r.total));
        const tra = median(results.map(r => r.tra));
        console.log(`| ${variant.name} | ${total.toFixed(0)}ms | ${tra.toFixed(0)}ms |`);
    }
}

Run with npm i url-utils-530@npm:@tryghost/url-utils@5.3.0 next to it, then node bench.js <path to packages/url-utils>.

Release notes

@tryghost/url-utils (minor, suggested 5.4.0)

Added urlUtils.freeze(), urlUtils.unfreeze(), urlUtils.isFrozen and a frozen constructor option. Freezing snapshots the site, subdirectory and admin URLs for setups where they never change at runtime.
Improved performance of transformReadyToAbsolute (~15× faster), replacePermalink (no per-call moment for permalinks without date tokens) and root URL parsing across the URL transform helpers.
No output changes.

To get the full benefit, Ghost should call urlUtils.freeze() (or pass frozen: true) once config is loaded in production. That will be a follow-up PR in Ghost.

This PR doesn't change the version. It should be a minor bump (5.4.0) since freeze() is new API, and that's handled after merge.

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Walkthrough

The changes add bounded caching for root URL parsing, subdirectory patterns, permalink patterns, and date formatters. URL conversion utilities use the shared root URL parser, while absolute transformation and permalink replacement use revised replacement logic. UrlUtils adds methods and a constructor option to snapshot URL getter values and restore live getters. Tests compare transformation and permalink results with legacy implementations and cover caching and freeze behavior.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Feature

Merge Risk: 🔵 Low · up to be8ab

This change speeds up URL handling and adds an opt-in freeze option. The main concern is that the new lru-cache dependency requires Node 20 or newer. Consumers on older Node versions may hit install warnings or failures. Declare the supported Node range or pick a compatible lru-cache version.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 53.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 15 functions across 21 files. (2 skipped:…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the primary change: performance improvements to url-utils for sitemap-scale workloads.
Description check	✅ Passed	The description directly explains the performance work, new freezing API, memoization, compatibility testing, benchmarks, and release considerations.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Explanation

Docstring coverage is 53.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 15 functions across 21 files. (2 skipped: 2 unsupported.)

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codecov-commenter · 2026-10-02T15:33:57Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (977078d) to head (43f6137).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1095   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           25        25           
  Lines         2223      2226    +3     
  Branches       328       331    +3     
=========================================
+ Hits          2223      2226    +3

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Ghost's sitemap build calls url-utils several times per post. Profiling a 300k-post site showed repeated getter calls (Ghost's getSubdir parses the configured url on every call) and repeated `new URL()` parsing of the same handful of root URLs as a large part of the cost. - added `freeze()`/`unfreeze()`/`isFrozen` and a `frozen` constructor option that snapshot `getSiteUrl`/`getSubdir`/`getAdminUrl`. Opt-in; unfrozen behaviour is unchanged - added `parseRootUrl`, a bounded cache of parsed root URLs, used wherever a root/base URL was parsed with `new URL()` - cached the subdirectory regex in `deduplicateSubdirectory` Both caches are pure functions of their input string so can't go stale. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Sitemaps call `transformReadyToAbsolute` twice per post (post url and feature image). Previously every call built three option objects and looked up the site url before the no-placeholder early return, then built a new RegExp and sliced the remainder of the string for every match. - `UrlUtils#transformReadyToAbsolute` returns early before computing the site url or options when there's nothing to replace, and builds its default asset options once rather than per call. Options are only merged when passed - the util now walks the string with `indexOf`, checks asset prefixes in place without slicing, and memoizes trailing-slash stripping of base urls Output is unchanged, verified by equivalence tests against the 5.3.0 implementation. Cuts `transformReadyToAbsolute` time on 300k posts from ~420ms to ~25ms. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

`replacePermalink` created a moment-timezone instance for every call, even for the default `/:slug/` permalink which has no date tokens (~160ms per 300k posts in sitemap builds). - date parts are now only computed when `:year`, `:month` or `:day` appear - they're formatted with a cached `Intl.DateTimeFormat('en-CA')` per timezone for Dates, timestamps and ISO 8601 strings with an explicit offset - other inputs (strings without an offset, which moment parses in the site timezone, invalid dates, years outside 1900-9999 and timezones Intl doesn't support) still go through moment-timezone so their output is unchanged. The dependency stays for that fallback Verified identical to the 5.3.0 output for every Intl timezone, for dates in every year from 1900 to 2100 including date-line and DST edges. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

`replacePermalink` ran its token regex and allocated a replace callback on every call. Sites only have a handful of permalink patterns, so each pattern is now split into literal and token parts once (bounded cache) and calls just concatenate the parts. 300k posts: `/:slug/` 32ms -> 4ms, `/:primary_tag/:slug/` 50ms -> 7ms, `/:year/:month/:day/:slug/` 185ms -> 109ms. Output is unchanged. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

The root URL, subdirectory regex and trailing-slash caches each had their own Map with clear-when-full eviction. They now share a small `memoize` helper backed by lru-cache, so frequently used entries are never evicted by a burst of unique inputs. Errors thrown by the memoized function are not cached. `parseRootUrl.clearCache()` is now `parseRootUrl.clear()`. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

- only Dates and timestamps use the cached `Intl.DateTimeFormat`, all strings go through moment. Drops the ISO-with-offset regex; Ghost passes `published_at` as a Date - the formatter and compiled permalink caches use the shared memoize helper, unsupported timezones throw and fall back to moment rather than being cached as `null` - dropped the en-CA output guard, the equivalence tests catch any change to the format - the Intl path is only used for timezones moment knows (Intl accepts some, e.g. `+01:00`, that moment treats as UTC) and when the active moment locale doesn't rewrite digits (e.g. `ar`), so output is unchanged for both Output is unchanged, still identical to 5.3.0 for every Intl timezone and every year from 1900 to 2100, and for every moment locale. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

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Inline comments:
Review comments at @packages/url-utils/package.json:
- Line 42: Update the package metadata for @tryghost/url-utils to declare the
Node engine range required by lru-cache@^11.0.0, or select an lru-cache version
compatible with the package’s existing supported Node versions.

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📒 Files selected for processing (23)

packages/url-utils/README.md
packages/url-utils/package.json
packages/url-utils/src/UrlUtils.ts
packages/url-utils/src/utils/absolute-to-relative.ts
packages/url-utils/src/utils/deduplicate-subdirectory.ts
packages/url-utils/src/utils/index.ts
packages/url-utils/src/utils/memoize.ts
packages/url-utils/src/utils/parse-root-url.ts
packages/url-utils/src/utils/plaintext-absolute-to-transform-ready.ts
packages/url-utils/src/utils/relative-to-absolute.ts
packages/url-utils/src/utils/relative-to-transform-ready.ts
packages/url-utils/src/utils/replace-permalink.ts
packages/url-utils/src/utils/strip-subdirectory-from-path.ts
packages/url-utils/src/utils/transform-ready-to-absolute.ts
packages/url-utils/src/utils/transform-ready-to-relative.ts
packages/url-utils/test/unit/url-utils.test.js
packages/url-utils/test/unit/utils/deduplicate-subdirectory.test.js
packages/url-utils/test/unit/utils/memoize.test.js
packages/url-utils/test/unit/utils/parse-root-url.test.js
packages/url-utils/test/unit/utils/replace-permalink-equivalence.test.js
packages/url-utils/test/unit/utils/transform-ready-to-absolute-equivalence.test.js
packages/url-utils/test/utils/legacy/replace-permalink.js
packages/url-utils/test/utils/legacy/transform-ready-to-absolute.js

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acburdine force-pushed the claude/url-utils-performance-fixes-0c4102 branch from 4433872 to 9e3f5ff Compare October 2, 2026 15:34

acburdine force-pushed the claude/url-utils-performance-fixes-0c4102 branch 4 times, most recently from 042e9be to 55fe49b Compare October 2, 2026 16:04

acburdine mentioned this pull request Oct 2, 2026

Stopped Renovate pinning runtime dependencies #1096

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acburdine force-pushed the claude/url-utils-performance-fixes-0c4102 branch 5 times, most recently from 65577ea to 43f6137 Compare October 2, 2026 16:30

acburdine marked this pull request as ready for review October 2, 2026 16:34

acburdine and others added 5 commits October 2, 2026 12:39

acburdine force-pushed the claude/url-utils-performance-fixes-0c4102 branch from 43f6137 to be8abbe Compare October 2, 2026 16:39

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acburdine merged commit 3b28b0f into main Oct 2, 2026
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acburdine deleted the claude/url-utils-performance-fixes-0c4102 branch October 2, 2026 17:00

This was referenced Oct 2, 2026

Updated @tryghost/url-utils to 5.4.0 and froze url getters TryGhost/Ghost#31293

Merged

Replaced moment-timezone with luxon in url-utils #1097

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Improved url-utils performance for sitemap-scale workloads - #1095

Improved url-utils performance for sitemap-scale workloads#1095
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