Basically the Unest exec plan could be made faster if we reduced some copies. Here is the basic idea in case anyone wants to do that

    // Create an array with the unnested values of the list array, given the list
    // array:
    //
    //   [1], null, [2, 3, 4], null, [5, 6]
    //
    // the result array is:
    //
    //   1, null, 2, 3, 4, null, 5, 6
    //
    let unnested_array = unnest_array(list_array)?;

This looks very much the same to me as calling list_array.values() to get access to the underlying values: https://docs.rs/arrow/latest/arrow/array/struct.GenericListArray.html#method.values

In this case the values array would be more like

[1, 2, 3, 4, 5, 6]

And the offsets of the list array would be would be like (I think):

[0, 1, 1, 3, 3, 6]

With a null mask showing the second and fourth element are null

So I was thinking you could calculate the take indices directly from the offsets / nulls without having to copy all the values out of the underlying array

Originally posted by @alamb in #6903 (comment)