felipecrv commented on code in PR #42010:
URL: https://github.com/apache/arrow/pull/42010#discussion_r1639039522
##########
cpp/src/arrow/pretty_print.cc:
##########
@@ -413,18 +414,36 @@ Status ArrayPrinter::WriteValidityBitmap(const Array&
array) {
}
}
+Result<std::shared_ptr<Array>> CopyStartEndToCPU(const Array& arr, int window)
{
+ std::shared_ptr<Array> arr_sliced;
+ if (arr.length() > (2 * window + 1)) {
+ ARROW_ASSIGN_OR_RAISE(auto arr_start,
+ arr.Slice(0, window +
1)->CopyTo(default_cpu_memory_manager()));
+ ARROW_ASSIGN_OR_RAISE(
+ auto arr_end,
+ arr.Slice(arr.length() - window -
1)->CopyTo(default_cpu_memory_manager()));
+ ARROW_ASSIGN_OR_RAISE(arr_sliced, Concatenate({arr_start, arr_end}));
+ } else {
+ ARROW_ASSIGN_OR_RAISE(arr_sliced,
arr.CopyTo(default_cpu_memory_manager()));
Review Comment:
> CopyTo just naively copies all buffers of the array in its entirety, not
actually truncating and copying only the part of the buffer that is needed?
Yes, because `MemoryManager`s work in terms of Buffers, not ranges. We
recently added a function that can copy slices to CPU, but it falls back to
full buffer copy if the source `MemoryManager` is not a CPU memory manager.
The protocols for memory movement between devices might not allow for
range-based copies (@zeroshade might know better than me), so instead expanding
the `MemoryManager` interface we should probably have a way to slice the array
where it is (device-specific) and then copy the smaller array. (?)
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