[Performance] Writing templates is slow because of unbounded concurrency

[shivjm]

trafficstars

Operating system

Windows 10

Eleventy

3.0.0-alpha.9

Describe the bug

This use of Promises:

https://github.com/11ty/eleventy/blob/9c3a7619a429f26cc2b449d65209be6d6a23828e/src/Template.js#L751

Means that almost all templates are written at the same time to the disk, which dramatically slows down individual writes. I added a console.time around the write to show this and recorded the output. You can see that some files take a full 15 seconds to write, and the total time for ‘Template Write’ is 15,885ms or nearly 16 seconds with 926 files.

For the sake of testing, I changed just that line to use fs.writeFileSync instead of await writeFile. Here’s the output. The time for ‘Template Write’ dropped to 232ms, with each individual file taking under a millisecond.

Reproduction steps

1. Create multiple template files.
2. Run Eleventy.

Expected behavior

Files are written sequentially or with bounded concurrency.

Reproduction URL

No response

Screenshots

No response

[shivjm]

I think fixing this would also fix #2627.

[zachleat]

Shipping your PR with 3.0.0-alpha.11