Taking TTFX seriously: Can we make common packages faster to load and use

General Usage Performance
29

Can we hack together some list of best practices, which could become a page in the docs? Turning the initial list into instructions or alternatively a “debug guide”:

How to write packages with good startup times

  1. Write type stable code whose return types can be inferred
  2. Avoid using Requires.jl, because enclosed code cannot be precompiled
  3. If possible, put widely used calls into a let block in the package main source file
  4. Use precompile for functions with side effects, avoid it for functions without.
  5. Avoid unnecessary dependencies
  6. Use ProfileView.@profview using YourPackage to visualize the loading process.
  7. …

i copied the list over here, where you can freely edit it and make corrections, if necessary, as I’m by no means an authority in this topic. Maybe we can turn this into a PR?

Regarding the last point: I just @profviewed one of my packages and the output is really hard to interpret. Are there any specific things to look out for? Currently, most of the time is spent in task.jl, poptask (80%) and loading.jl, _tryrequire_from_serialized (20%) - which tells me nothing, does it?

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