paleolimbot commented on code in PR #48002: URL: https://github.com/apache/arrow/pull/48002#discussion_r2546854150
########## docs/source/format/CanonicalExtensions.rst: ########## @@ -544,6 +544,49 @@ Primitive Type Mappings | UUID extension type | UUID | +----------------------+------------------------+ +.. _timestamp_with_offset_extension: + +Timestamp With Offset +============= +This type represents a timestamp column that stores potentially different timezone offsets per value. The timestamp is stored in UTC alongside the original timezone offset in minutes. +This extension type is intended to be compatible with ANSI SQL's ``TIMESTAMP WITH TIME ZONE``, which is supported by multiple database engines. + +* Extension name: ``arrow.timestamp_with_offset``. + +* The storage type of the extension is a ``Struct`` with 2 fields, in order: + + * ``timestamp``: a preferably non-nullable ``Timestamp(time_unit, "UTC")``, where ``time_unit`` is any Arrow ``TimeUnit`` (s, ms, us or ns). + + * ``offset_minutes``: a preferably non-nullable signed 16-bit integer (``Int16``) representing the offset in minutes from the UTC timezone. Negative offsets represent time zones west of UTC, while positive offsets represent east. Offsets range from -779 (-12:59) to +780 (+13:00). + +* Extension type parameters: + + * ``time_unit``: the time-unit of each of the stored UTC timestamps. + +* Description of the serialization: + + Extension metadata is an empty string. + +.. note:: + + It is also *permissible* for the ``offset_minutes`` field to be dictionary-encoded or run-end-encoded. + +.. note:: + + It is also *permissible* for ``timestamp`` and ``offset_minutes`` to be nullable, but not recommended. + + If ``timestamp`` is nullable and a value is found to be null, then the whole ``TimestampWithOffset`` value should be interpreted as null. One way of achieving this is to drop ``timestamp``'s validity buffer (V1) and replace the top-level struct's validity buffer (V2) with the result of ``V1 AND V2``. + + If ``offset_minutes`` is nullable and a value is found to be null, then this value should be interpreted as if the offset value were were zero. Review Comment: > Why not mandate that struct fields are always non-null +1. I had the same worry when we decided to make all of GeoArrow's native memory layouts have non-nullable children...the language in GeoArrow is that children must not contain nulls. When producing, all the implementations explicitly mark fields as non-nullable. When consuming, they check for a zero null count. Specifying anything about the specific arrangement of buffers I think is out of scope for an extension type definition (if we want to do this, somebody has to make sure it can be done in places like DuckDB, JavaScript, and Julia that might not offer the same level of control over buffer creation). -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
