Performance issue on relatively small file

[Porges]

Describe the bug

Parsing the file located here with yaml.parse(str, {merge:true}) takes a very long time. Could there be something non-linear in the length of the file?

Currently it's under 500k:

$ wc bibliography.yaml
 18610  48360 489877 bibliography.yaml

To Reproduce
Steps to reproduce the behaviour.

const yaml = require('yaml');
const fs = require('fs');

fs.readFile("bibliography.yaml", 'utf8', (_, data) => {
    console.time('yaml-parse');
    const loaded = yaml.parse(data, {merge: true});
    console.timeEnd('yaml-parse');
});

Output:

yaml-parse: 10.501s

Expected behaviour
A clear and concise description of what you expected to happen.

By comparison, doing the same thing with js-yaml takes only:

const yaml = require('js-yaml');
const fs = require('fs');

fs.readFile("bibliography.yaml", 'utf8', (_, data) => {
    console.time('yaml-load');
    const loaded = yaml.load(data);
    console.timeEnd('yaml-load');
});

Output:

yaml-load: 125.814ms

Versions (please complete the following information):

• Environment: Node v18.17.1
• yaml: 2.4.1

Additional context
Add any other context about the problem here.

[eemeli]

Interesting. Thank you for sharing the file that's demonstrating this! Looks like the slowdown is during the document -> JS conversion. Probably due to the alias resolution?

I'll see when I can find time to dig into this properly; might take a while.

[rejetto]

loading a 3.7MB file of a simple single-level dictionary was taking 77 seconds on my machine fast mac (m1 max).
i unexpectedly solved it by reading the file line by line, and parsing each line. Now it's 3 seconds, 25x difference. 👀
of course this is not a solution unless you are in my same situation, but i wanted to share my experience, as it can shed some light on the problem.

[eemeli]

@rejetto Do you mean parsing each line as a separate YAML document?

[rejetto]

yes, invoking parse on the single line.
It's weird, and i don't have time to dig it more, but since it's hard to expect i thought good to share this information.
my dictionary is made of a file path for the key and a number for the value.