issue_comments: 642953710

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https://github.com/pydata/xarray/issues/4147#issuecomment-642953710 https://api.github.com/repos/pydata/xarray/issues/4147 642953710 MDEyOklzc3VlQ29tbWVudDY0Mjk1MzcxMA== 14808389 2020-06-11T22:02:38Z 2020-06-11T22:02:38Z MEMBER

It seems that's because adding (potentially big) Dataset / DataArray objects using https://github.com/pydata/xarray/blob/4071125feedee690364272e8fde9b94866f85bc7/xarray/core/parallel.py#L39-L40 is really slow and the stacktrace from sending KeyboardInterrupt says that _iter is called (if I understand it correctly, that is iterating over all values of the DataArray / Dataset using a python loop).

Looking at the code of map_blocks, the object arrays (npargs ) is only used because of its indexing and we might be able to use a list / tuple and itertools to get the same result, but without iterating over values. Am I missing something? cc @dcherian

 
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