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Hang in GC with groupby #288

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krynju opened this issue Oct 13, 2021 · 0 comments
Closed

Hang in GC with groupby #288

krynju opened this issue Oct 13, 2021 · 0 comments

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@krynju
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krynju commented Oct 13, 2021

julia -t16 - many threads

using Dagger
nt = (a=rand(Int, 100_000_000).%1000,)
d = DTable(nt, 1_000_000)
Dagger.groupby(d, :a)
Dagger.groupby(d, :a)
Dagger.groupby(d, :a)
Dagger.groupby(d, :a)

observations:

  • multiple threads (usually 3-4) actively waiting (pinned 100%) on a gc_safepoint (they want to run gc)
  • one thread stuck in gc - gdb observations - constantly switch between enable_finalizers/disable_finalizers
  • never ends, stuck forever
  • happens on both windows, linux
  • only heavily multithreaded, low thread count doesn't seem to trigget it that much
  • disabling GC for the groupby results in a pass

ideas:

  • absolutely none
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