Extreme slowdown in IndexedTable creation with CategoricalArrays

Hello, after a discussion with @piever , he suggested I open an issue with StructArrays. A recent update to CategoricalArrays has created an extreme slowdown of the IndexedTables/JuliaDB table() function. The full details of that conversation can be found on this open issue posted on JuliaDB.

The short version is (with a MWE):

using JuliaDB, BenchmarkTools, CategoricalArrays

function tabletest()
    names = fill.(["red","blue","green"], 150000) |> Base.Iterators.flatten |> collect
    loci = "loc".*string.(collect(1:1500))
    loci = fill.(loci, 300) |> Base.Iterators.flatten |> collect
    genotypes = fill((1,2), 450000)

    return table((names = names, loci = loci, genotypes = genotypes), pkey = :names)
end

function tabletest_cat()
    names = fill.(["red","blue","green"], 150000) |> Base.Iterators.flatten |> collect
    loci = "loc".*string.(collect(1:1500))
    loci = fill.(loci, 300) |> Base.Iterators.flatten |> collect
    genotypes = fill((1,2), 450000)

    return table(
            (names = categorical(names, compress = true), 
            loci = categorical(loci, compress = true), 
            genotypes = genotypes),
            pkey = :names
        )
end

julia> @benchmark tabletest()
BenchmarkTools.Trial: 
  memory estimate:  79.81 MiB
  allocs estimate:  900109
  --------------
  minimum time:     246.040 ms (7.45% GC)
  median time:      270.271 ms (12.39% GC)
  mean time:        280.085 ms (15.80% GC)
  maximum time:     436.054 ms (44.68% GC)
  --------------
  samples:          18
  evals/sample:     1

Howerver, doing @benchmark tabletest_cat() has been running for several hours and hadn't finished by the time I killed the job, which is probably not a good sign.

Start by running the provided tabletest() and tabletest_cat() benchmarks with JuliaDB, BenchmarkTools, and CategoricalArrays. Read the table() path in StructArrays and the linked JuliaDB issue to understand how categorical columns are handled. Done means categorical table creation completes without the reported extreme slowdown.