Docusaurus leaks memory on i18n site builds

[slorber]

When building a Docusaurus site with multiple locales, the memory keeps increasing.

What happens, in pseudo-code:

async function buildSite() {
  await buildLocale("en"); // +20mb
  await buildLocale("fr"); // +20mb
  await buildLocale("ja"); // +20mb
  await buildLocale("es"); // +20mb
}

This can be seen on our website, but also our init template (much smaller leak though).

In #10599 we solved an important leak, but we still leak memory and should investigate so that it's possible to build a Docusaurus site in thousands of locales without having to increase the heap size.

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Repro

yarn install

yarn clear:website

NODE_OPTIONS="--max-old-space-size=250 --expose-gc" DOCUSAURUS_PERF_LOGGER=true yarn build:website:fast --locale en --locale fr --locale ja --locale es

The logs show memory increasing after each locale despite calling globalThis.gc?.() before measures.

[PERF] Build > en - 20.90 seconds! - (58mb -> 144mb)
[PERF] Build > fr - 30.94 seconds! - (144mb -> 162mb)
[PERF] Build > ja - 32.49 seconds! - (162mb -> 180mb)
[PERF] Build > es - 33.00 seconds! - (180mb -> 197mb)
[PERF] Build - 117.36 seconds! - (58mb -> 197mb)

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Heap dumps

Heap dumps can be taken after each locale build with little edits in packages/docusaurus/src/commands/build/build.ts

async function runBuildLocaleTask(params: BuildLocaleParams) {
  await buildLocale(params);

  globalThis.gc?.();
  require('v8').writeHeapSnapshot(
    `docusaurus-heap-${Date.now()}-${params.locale}.heapsnapshot`,
  );
}

Access upon request: https://drive.google.com/drive/folders/11JrI_sgw_uwtGBAza52AEyVpiH33Qyq8?usp=sharing

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Edit: from this discussion, we can assume that the memory leak grows with the number of MDX docs:
#9211 (reply in thread)

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Edit: these articles presents interesting ways to run memory leak tests:

• https://joyeecheung.github.io/blog/2024/03/17/memory-leak-testing-v8-node-js-1/
• https://joyeecheung.github.io/blog/2024/03/17/memory-leak-testing-v8-node-js-2/
• https://joyeecheung.github.io/blog/2024/03/17/memory-leak-testing-v8-node-js-3/