Storybook >10 seconds to launch, slowed down by merge in transformStoriesRawToStoriesHash

[koop-stripe]

Describe the bug
Storybook takes 10-15 seconds to launch in production. Most of the time (7-10 seconds) is spent in transformStoriesRawToStoriesHash repeatedly calling merge.

Screenshots of both are provided below. This only occurs for us when building for production. We have 505 stories in our storybook.

To Reproduce
Steps to reproduce the behavior:

1. Build storybook for production build-storybook --docs -c .storybook -o .storybook-dist
2. Start the server, load a page in your browser.
3. Wait 10-15 seconds until the page loads.

Update: I've since confirmed that this also occurs in development mode.

Expected behavior
Don't wait 10-15 seconds. 😛

Screenshots
Full performance view:

Zoomed in on baseMerge calls:

System:
System:
OS: macOS 10.15.4
CPU: (8) x64 Intel(R) Core(TM) i7-7920HQ CPU @ 3.10GHz
Binaries:
Node: 10.16.0 - ~/.nodenv/versions/10.16.0/bin/node
Yarn: 1.19.1 - ~/.yarn/bin/yarn
npm: 6.9.0 - ~/.nodenv/versions/10.16.0/bin/npm
Browsers:
Chrome: 83.0.4103.116
Firefox: 78.0.1
Safari: 13.1
npmPackages:
@storybook/addon-docs: 6.0.0-rc.5 => 6.0.0-rc.5
@storybook/react: 6.0.0-rc.5 => 6.0.0-rc.5

[blaine-stripe]

@shilman Your PR helped a bunch, especially around the stories hash, but it seems that 7 seconds are still being spent in configure on page load.

[shilman]

Egads!! I just released https://github.com/storybookjs/storybook/releases/tag/v6.0.0-rc.16 containing PR #11707 that references this issue. Upgrade today to try it out!

You can find this prerelease on the @next NPM tag.

Closing this issue. Please re-open if you think there's still more to do.

[shilman]

Yippee!! I just released https://github.com/storybookjs/storybook/releases/tag/v6.0.0-rc.20 containing PR #11740 that references this issue. Upgrade today to try it out!

You can find this prerelease on the @next NPM tag.

Closing this issue. Please re-open if you think there's still more to do.