tustvold commented on code in PR #37877:
URL: https://github.com/apache/arrow/pull/37877#discussion_r1343253323
##########
docs/source/format/Columnar.rst:
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@@ -487,6 +499,102 @@ will be represented as follows: ::
|-------------------------------|-----------------------|
| 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 | unspecified (padding) |
+ListView Layout
+~~~~~~~~~~~~~~~
+
+The ListView layout is defined by three buffers: a validity bitmap, an offsets
+buffer, and an additional sizes buffer. Sizes and offsets have the identical
bit
+width and both 32-bit and 64-bit signed integer options are supported.
+
+As in the List layout, the offsets encode the start position of each slot in
the
+child array. In contrast to the List layout, list lengths are stored explicitly
+in the sizes buffer instead of inferred. This allows offsets to be out of
order.
+Elements of the child array do not have to be stored in the same order they
+logically appear in the list elements of the parent array.
+
+When a value is null, the corresponding offset and size can have arbitrary
+values. When size is 0, the corresponding offset can have an arbitrary value.
+If choosing a value is possible, we recommend setting offsets and sizes to 0 in
Review Comment:
Agreed, many kernels in arrow-rs do still handle the null mask, or some
similar mask derived from the inputs, but make use CLZ tricks to iterate it
efficiently. This in turn requires providing an API for value access, that
doesn't itself then check the null mask, and in order for this to be safe we
need the invariants to hold for non-null values :smile:
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