How mongoose handle async parallel changes?

Question

I'm working with nodejs and mongodb (using mongoose pkg).

I've an async function which updates a document. I'm running that function 10 times with different parameter in parallel. My question is that will mongoose/mongodb auto fetch the document again before saving if it's already saved before. Or will it throw an error?

Here's my code

const crawlSitemap = async (projectId) => {
  try {
    const project = await Project.findById(projectId);
    const browser = await puppeteer.launch({ headless: "new" });

    const crawl = (sitemap) => async () => {
      const page = await browser.newPage();
      page.setDefaultNavigationTimeout(120 * 1000);
      console.log(sitemap.url);
      if (!validator.isURL(sitemap.url) || sitemap.crawlStatus !== "queued")
        return;
      await page.goto(sitemap.url, { waitUntil: "networkidle0" });
      await page.evaluate(() => {
        const scripts = document.querySelectorAll("script");
        scripts.forEach((script) => script.remove());

        const images = document.querySelectorAll("img");
        images.forEach((img) => img.remove());

        const styles = document.querySelectorAll(
          'link[rel="stylesheet"], style'
        );
        styles.forEach((style) => style.remove());
      });
      const textContent = await page.evaluate(() => document.body.textContent);
      await page.close();

      await promisify(fs.writeFile)(
        path.join(__dirname, `tmp/${sitemap.url.replaceAll("/", "-")}.txt`),
        textContent,
        "utf-8"
      );
      sitemap.crawlStatus = "ok";
      await project.save();
    };

    await parallelLimit(project.sitemap.map(crawl), 10);

    await browser.close();
  } catch (error) {
    console.log(error);
  }
};

Answer 1

Mongoose isn't designed to call save in parallel multiple times on the same instance.

You can try instead findOneAndUpdate every time you'd like to change sitemap status:

const crawl = (sitemap) => async () => {
      const page = await browser.newPage();

      // ...

      // Instead of this:
      //
      // sitemap.crawlStatus = "ok";
      // await project.save();

      // Do this:
      await Project.findOneAndUpdate(
        {
          _id: project.
          'sitemap.url': sitemap.url
        },
        {
          'sitemap.$.crawlStatus': 'ok'
        }
      );  
    };