Hi Antoine, Thank you for the quick response and for clarifying the use case!
I agree that it would be more accurate to write the Arrow Time type to Parquet with `isAdjustedToUTC=false`. My understanding is that this is not the default behavior due to the requirements specified by the Parquet Compatibility Guidelines regarding the deprecation of TIME_MILLIS and TIME_MICROS[1]. At least, that was my takeaway from this discussion[2], but please correct me if I'm wrong. Given this context, it seems adding a flag to the Arrow Parquet writer to let users control the `isAdjustedToUTC` value would be a reasonable enhancement. Thanks again! Best, Sarah [1] https://github.com/apache/parquet-format/blob/master/LogicalTypes.md#deprecated-time-convertedtype [2] https://github.com/apache/arrow/issues/41476#issuecomment-2088094499 ________________________________________ From: Antoine Pitrou <anto...@python.org> Sent: Thursday, August 21, 2025 5:55 AM To: d...@parquet.incubator.apache.org <d...@parquet.incubator.apache.org> Subject: Re: Purpose of the isAdjustedToUTC TIME parameter Hi Sarah, Thanks for bringing this to our attention. I had missed the Arrow PR. As for the Parquet spec, the purpose of the `isAdjustedToUTC` flag seems clear: * if `isAdjustedToUTC` is true, the TIME value is expressed in reference to midnight in the UTC timezone * if `isAdjustedToUTC` is false, the TIME value is expressed in reference to midnight in an unknown timezone (presumably the "local timezone" where the measurements were made) As for the Arrow behavior, the Arrow Time type actually doesn't reference UTC. So, as I've argued on the PR, the Arrow Time type should probably be written to Parquet with `isAdjustedToUTC=false`. Regards Antoine. On Wed, 20 Aug 2025 14:18:59 +0000 Sarah Gilmore <sgilm...@mathworks.com.INVALID> wrote: > Hi all, > I recently opened a pull request[1] in the apache/arrow project to extend the > Arrow Parquet writer to support writing TIME data with isAdjustedToUTC=false. > For your reference, the Arrow Parquet writer defaults to exporting Arrow time > data as Parquet TIME data with isAdjustedToUTC=true, even though Arrow time > types are timezone-agnostic, in order to follow the Parquet Compatibility > Guidelines[2] regarding the deprecation of ConvertedTypes TIME_MILLIS and > TIME_MICROS. > However, progress on this pull request has stalled because the Arrow > community is confused about the purpose of the isAdjustedToUTC parameter[3], > and some members think the best strategy moving forward would be to deprecate > it[4]. > Could the Parquet community provide some background about why the TIME type > is parameterized on isAdjustedToUTC? Are there plans to deprecate this > parameter in the future? > Any information the community can provide would be much appreciated, because > it will help the Arrow community decide whether it makes sense to add a flag > for controlling this parameter to the Arrow Parquet writer. > I appreciate the community's time and thoughts on this issue. > Thank you! > Best, > Sarah Gilmore > [1] https://github.com/apache/arrow/pull/47316 > [2] > https://github.com/apache/parquet-format/blob/master/LogicalTypes.md#deprecated-time-convertedtype > [3] https://github.com/apache/arrow/pull/43268#discussion_r1686692052 > [4] https://github.com/apache/arrow/pull/47316#issuecomment-3190380012 > >
