plots_repro.md

Plots.jl precompile issue

• Create LocalPreferences.toml with

  [PrecompileTools]
  precompile_workloads = false

• Install Plots + HTTP.
• Run julia +1.10 --project --trace-compile=plots_compile.jl
• Run the following:

julia> @time using Plots
  0.740981 seconds (768.54 k allocations: 57.182 MiB, 0.84% gc time, 6.02% compilation time)

julia> @time @eval (p = Plots.plot(rand(10), rand(10)); display(p));
  3.452190 seconds (20.40 M allocations: 1.374 GiB, 7.79% gc time, 92.98% compilation time: <1% of which was recompilation)

Make sure the TTFP is slow so to ensure that the precompile workload disabling was effective (cf JuliaLang/PrecompileTools.jl#62). This should generate a plots_compile.jl with ~ 504 statements.

---

Import precompile file:

• Start julia: julia +1.10 --project --trace-compile=plots_compile_after_include.jl
• Run the following:

julia> using Plots, HTTP

julia> for mod in Base.loaded_modules_order
           if !(nameof(mod) in (:Main, :Core, :Base))
               Core.eval(@__MODULE__, :(const $(Symbol(mod)) = $mod))
           end
       end

julia> @time include("plots_compile.jl")
  3.429380 seconds (20.86 M allocations: 1.405 GiB, 8.20% gc time, 97.42% compilation time)
true

julia> g() = rand()

julia> g()

julia> @time @eval (p = Plots.plot(rand(10), rand(10)); display(p));
  0.292021 seconds (141.86 k allocations: 9.912 MiB, 22.93% compilation time)

• Open up the plots_compile_after_include.jl and find the precompile(Tuple{typeof(Base.rand), Int64}) call and delete everything above it, resulting file will have ~18 signatures.

---

Now run: julia +1.10 --project

julia> using Plots, HTTP

julia> for mod in Base.loaded_modules_order
           if !(nameof(mod) in (:Main, :Core, :Base))
               Core.eval(@__MODULE__, :(const $(Symbol(mod)) = $mod))
           end
       end

julia> @time include("plots_compile.jl")
  3.767446 seconds (20.67 M allocations: 1.392 GiB, 8.30% gc time, 97.37% compilation time)
true

julia> @time include("plots_compile_after_include.jl")
  0.053578 seconds (128.33 k allocations: 8.950 MiB, 91.61% compilation time)
true

julia> @time @eval (p = Plots.plot(rand(10), rand(10)); display(p));
  0.237858 seconds (16.35 k allocations: 1.159 MiB, 2.42% compilation time)

Note the low compilation time on the plot call compared to earlier. Also, note how including the full plots_compile.jl twice does not work:

julia> using Plots, HTTP

julia> for mod in Base.loaded_modules_order
           if !(nameof(mod) in (:Main, :Core, :Base))
               Core.eval(@__MODULE__, :(const $(Symbol(mod)) = $mod))
           end
       end

julia> @time include("plots_compile.jl")
  3.697584 seconds (20.67 M allocations: 1.392 GiB, 8.27% gc time, 97.31% compilation time)
true

julia> @time include("plots_compile.jl")
  0.093587 seconds (78.69 k allocations: 4.360 MiB)
true

julia> @time @eval (p = Plots.plot(rand(10), rand(10)); display(p));
  0.298213 seconds (142.06 k allocations: 9.929 MiB, 21.79% compilation time)

Open questions:

• Why does replaying the precompile file not remove virtually all compilation time?
• Why is it required to only execute a part of the precompile statements twice to remove the compilation time? What is it about the earlier ones that causes the latter ones to not be effective?
• Is there something special about the signatures of the functions that fail to cache?