FWIW, iceberg-cpp also produces a date type for the day transform so we are happy with the consensus here.
On Sat, May 23, 2026 at 12:14 AM Kevin Liu <[email protected]> wrote: > > Good to know about the Avro spec behavior, thanks Ryan. > > And thank you Andrei for driving the spec clarification. I'll comment on the > PR. I don't think we need a vote since this is a clarification and not a > change. > > On Thu, May 21, 2026 at 1:42 PM Andrei Tserakhau via dev > <[email protected]> wrote: >> >> Thanks Kevin, Fokko, and Ryan, looks like we've converged. >> >> Summary of where this lands: >> >> - Result type for day becomes date, matching Java/PyIceberg/Rust's >> default behavior and the Avro types table in Appendix A. >> - Reader tolerance for historical plain-int manifests is inherited >> from the Avro spec itself (thanks Ryan for surfacing that saves >> us an Iceberg-side MUST clause). >> - A short note is added under the partition transforms table >> capturing the historical context, so this doesn't get re-litigated >> the next time someone reads the spec without the back-story. >> >> PR is updated accordingly: https://github.com/apache/iceberg/pull/16446 >> >> Fokko, Kevin, Ryan -- would appreciate a look when you have a moment. >> Happy to iterate further on the note wording if anything reads off. >> >> For iceberg-go, I'll follow up with the writer + reader alignment >> (PR #915 in iceberg-go is already in flight) once the spec change >> lands. >> >> Best, >> Andrei >> >> On Thu, May 21, 2026 at 9:41 PM Ryan Blue <[email protected]> wrote: >>> >>> Ugh, I think I sent from the wrong email address and my reply didn't go >>> through. >>> >>> Other people have covered the same things here, except for one point: the >>> Avro spec states that readers that don't support an annotation are required >>> to ignore it. So the behavior to read either date or int correctly is >>> inherited from the Avro spec. >>> >>> Ryan >>> >>> On Thu, May 21, 2026 at 10:17 AM Kevin Liu <[email protected]> wrote: >>>> >>>> I wasn’t aware of the previous back-and-forth changes to this line in the >>>> spec. Thanks for the extra context! >>>> >>>> A couple of points I want to align on: >>>> 1. All implementations except Go, including Java, Python, and Rust, write >>>> the day transform result as an Iceberg date type. That maps to the Avro >>>> date type and is serialized as { "type": "int", "logicalType": "date" }. >>>> 2. The Go implementation writes the day transform result an Iceberg int >>>> type. That maps to the Avro int type and is serialized as { "type": "int" >>>> }. >>>> 3. Java, Python, and Rust can read Avro manifest partition values as >>>> either an Avro int type or an Avro date type. >>>> 4. The Go implementation can currently read Avro manifest partition values >>>> only as an Avro int type. This is the original issue that sparked this >>>> conversation. >>>> >>>> Since the spec has gone back and forth between writing this as an Iceberg >>>> int and an Iceberg date, I think readers must accept both. We can include >>>> that as an implementation note. >>>> >>>> I support changing the spec back to date so it matches the default >>>> behavior for day partition values in our implementations. Go is also >>>> making the change to write date instead of int. >>>> The other approach, updating all implementations to match the current >>>> spec, would be a lot of work for little value. >>>> >>>> Hopefully this is the last time we make this change to the spec :) >>>> Would love to hear from others. >>>> >>>> Best, >>>> Kevin Liu >>>> >>>> On Wed, May 20, 2026 at 10:39 AM Fokko Driesprong <[email protected]> wrote: >>>>> >>>>> > It wouldn't be the first time we've retroactively updated the spec when >>>>> > finding inconsistencies with the current implementations :P >>>>> >>>>> I think generally we try to avoid this, but in this case it was changed >>>>> to few times :P Maybe we should revert the spec change: >>>>> >>>>> https://github.com/apache/iceberg/pull/5980/changes#diff-36347a47c3bf67ea2ef6309ea96201814032d21bb5f162dfae4045508c15588a >>>>> >>>>> Curious to hear what other think. >>>>> >>>>> Kind regards, >>>>> Fokko >>>>> >>>>> >>>>> On 2026/05/20 17:24:22 Matt Topol wrote: >>>>> > It wouldn't be the first time we've retroactively updated the spec >>>>> > when finding inconsistencies with the current implementations :P >>>>> > >>>>> > Particularly, in this case even the "reference implementation" (i.e. >>>>> > Java) is technically not spec-compliant since the spec says that it >>>>> > should be an "int", not an Avro "date" type. If all the >>>>> > implementations currently write a "date" type, then it's silly to have >>>>> > to say that every implementation is violating the spec. >>>>> > >>>>> > If we want the spec to say it should be an int, but tolerate reading >>>>> > an Avro "date" type, that's fine. But that would mean we should update >>>>> > Java, Rust, and PyIceberg to all write plain "int" and no longer write >>>>> > the "date" type, again: it would be silly to say that the reference >>>>> > implementation and 2 other implementations are not following the spec. >>>>> > :P >>>>> > >>>>> > I agree that it would be a big change for little value to update the >>>>> > implementations, so my opinion is that the spec should be updated to >>>>> > either say that "either" is allowed to be written, or that "date" >>>>> > should be written but "int" should be allowed to be read. >>>>> > >>>>> > --Matt >>>>> > >>>>> > On Wed, May 20, 2026 at 1:05 PM Fokko Driesprong <[email protected]> >>>>> > wrote: >>>>> > > >>>>> > > Thanks for the quick PR Andrei. >>>>> > > >>>>> > > The problem is that the note conflicts with the Avro/Iceberg types >>>>> > > table: https://iceberg.apache.org/spec/#avro >>>>> > > >>>>> > > I don't think we want to update the implementations as I agree that >>>>> > > it would be a big change for little value. At the same time, I don't >>>>> > > think we can retroactively update the spec. Maybe an implementation >>>>> > > note would be a better solution to halt the tradition? >>>>> > > >>>>> > > Kind regards, >>>>> > > Fokko >>>>> > > >>>>> > > >>>>> > > On 2026/05/20 16:49:29 Andrei Tserakhau via dev wrote: >>>>> > > > Thanks Fokko, the historical context! >>>>> > > > >>>>> > > > Quick check that we're aligned, since I think we may be closer than >>>>> > > > it reads: >>>>> > > > >>>>> > > > My PR leaves the result type table as `int` -- no change to the >>>>> > > > transform table, no impact on hour/month/etc., no change to the >>>>> > > > type model. >>>>> > > > >>>>> > > > What the PR clarifies is the Avro encoding used when serializing a >>>>> > > > `day` partition field into a manifest. Empirically today, Java, >>>>> > > > PyIceberg, and Rust all write `{ "type": "int", "logicalType": >>>>> > > > "date" }` >>>>> > > > there (TypeToSchema in Java, DayTransform.result_type in PyIceberg, >>>>> > > > Transform::Day.result_type in Rust all produce a Date). Only >>>>> > > > iceberg-go produces plain Avro `int`. The PR codifies the de facto >>>>> > > > writer behavior as SHOULD and makes reader tolerance MUST. >>>>> > > > >>>>> > > > If your "stick with int" also covers the Avro annotation, then we'd >>>>> > > > effectively be reverting three writers and orphaning every existing >>>>> > > > manifest, which I don't think decent path, it's quite a big change >>>>> > > > for small benefits. >>>>> > > > >>>>> > > > Either way, super happy to adjust the spec adjustment, the goal is >>>>> > > > to >>>>> > > > stop this tradition of re-litigating issue every year, by misreading >>>>> > > > this part of the spec. >>>>> > > > >>>>> > > > Best, >>>>> > > > Andrei >>>>> > > > >>>>> > > > On Wed, May 20, 2026 at 6:37 PM Fokko Driesprong <[email protected]> >>>>> > > > wrote: >>>>> > > > >>>>> > > > > Thanks for briging this up Kevin, a gift that keeps on giving :) >>>>> > > > > https://github.com/apache/iceberg/issues/10616#issuecomment-2200191427 >>>>> > > > > >>>>> > > > > 1. I think we should stick with the int type as defined in the >>>>> > > > > spec. >>>>> > > > > 2. It feels to me that some readers are more permissive here than >>>>> > > > > others. >>>>> > > > > I believe some allow reading date as an int without throwing. >>>>> > > > > Practically, >>>>> > > > > readers should read both. >>>>> > > > > 3. Unfortunally, I think this is water under the bridge. As shown >>>>> > > > > above in >>>>> > > > > the GitHub Issue, we went back and forth, so I don't see a lot of >>>>> > > > > value in >>>>> > > > > switching this to date. All OSS implementations handle this as an >>>>> > > > > int >>>>> > > > > internally, and this also aligns with hour/month/etc. >>>>> > > > > >>>>> > > > > Hope this historical context helps. >>>>> > > > > >>>>> > > > > Kind regards, >>>>> > > > > Fokko >>>>> > > > > >>>>> > > > > >>>>> > > > > On 2026/05/20 16:33:51 Andrei Tserakhau via dev wrote: >>>>> > > > > > Here is a fast follow with a PR: >>>>> > > > > > https://github.com/apache/iceberg/pull/16446 >>>>> > > > > > >>>>> > > > > > Best, >>>>> > > > > > Andrei >>>>> > > > > > >>>>> > > > > > On Wed, May 20, 2026 at 6:11 PM Andrei Tserakhau < >>>>> > > > > > [email protected]> wrote: >>>>> > > > > > >>>>> > > > > > > Thanks for raising this, Kevin. >>>>> > > > > > > >>>>> > > > > > > Speaking as an iceberg-go maintainer, even though Go is the >>>>> > > > > > > implementation that has to move, I'd vote: >>>>> > > > > > > >>>>> > > > > > > 1. Writers SHOULD emit { "type": "int", "logicalType": "date" >>>>> > > > > > > }. >>>>> > > > > > > 2. Readers MUST accept both plain `int` and `int` annotated >>>>> > > > > > > with >>>>> > > > > > > `logicalType: date`. >>>>> > > > > > > 3. Keep the transform result type table as-is (`int` as the >>>>> > > > > > > logical >>>>> > > > > > > Iceberg type). Don't change it to `date`. Add a separate, >>>>> > > > > > > normative >>>>> > > > > > > manifest-encoding clause so projection and >>>>> > > > > > > expression-evaluation >>>>> > > > > > > semantics that depend on the type model stay untouched. >>>>> > > > > > > >>>>> > > > > > > Reasoning: when Java, PyIceberg, and Rust all write logical >>>>> > > > > > > `date`, >>>>> > > > > > > that's the de facto wire format. Forcing them to switch to >>>>> > > > > > > plain `int` >>>>> > > > > > > to match a literal reading of the transform table would churn >>>>> > > > > > > three >>>>> > > > > > > implementations and leave every existing manifest >>>>> > > > > > > "non-conforming" >>>>> > > > > > > forever. Aligning Go with the dominant writer convention >>>>> > > > > > > costs one >>>>> > > > > > > implementation change (PR #915 already proposes it) and zero >>>>> > > > > > > historical >>>>> > > > > > > churn. >>>>> > > > > > > >>>>> > > > > > > The underlying ambiguity is that "result type" (logical >>>>> > > > > > > Iceberg type) >>>>> > > > > > > and "Avro manifest encoding" (wire format) were conflated. >>>>> > > > > > > Separating >>>>> > > > > > > them in spec text removes the ambiguity without changing the >>>>> > > > > > > type >>>>> > > > > > > system. >>>>> > > > > > > >>>>> > > > > > > Happy to drive the spec PR and then iceberg-go writer + reader >>>>> > > > > > > alignment. >>>>> > > > > > > >>>>> > > > > > > Best, >>>>> > > > > > > Andrei >>>>> > > > > > > >>>>> > > > > > > On Tue, May 19, 2026 at 5:45 PM Kevin Liu >>>>> > > > > > > <[email protected]> >>>>> > > > > wrote: >>>>> > > > > > > >>>>> > > > > > >> Hi all, >>>>> > > > > > >> >>>>> > > > > > >> I'd like to invite the community to discuss a spec ambiguity >>>>> > > > > > >> in Apache >>>>> > > > > > >> Iceberg that has caused some confusion across >>>>> > > > > > >> implementations. We've >>>>> > > > > seen >>>>> > > > > > >> this come up in Python, Rust, and now Go. >>>>> > > > > > >> >>>>> > > > > > >> The issue: the spec documents the `day` partition >>>>> > > > > > >> transform's result >>>>> > > > > type >>>>> > > > > > >> as plain `int`, but Java, PyIceberg, and Rust all write >>>>> > > > > > >> manifest >>>>> > > > > partition >>>>> > > > > > >> fields using Avro's logical `date` type. Go currently writes >>>>> > > > > > >> plain >>>>> > > > > `int`, >>>>> > > > > > >> which is the strict reading of the spec. Since both forms >>>>> > > > > > >> have the >>>>> > > > > same >>>>> > > > > > >> physical representation, the difference is only the Avro >>>>> > > > > > >> schema >>>>> > > > > annotation >>>>> > > > > > >> -- but it's worth clarifying the spec so all implementations >>>>> > > > > > >> are >>>>> > > > > aligned. >>>>> > > > > > >> >>>>> > > > > > >> The full analysis, including a breakdown of each >>>>> > > > > > >> implementation's >>>>> > > > > > >> writer/reader behavior and proposed resolution options, is >>>>> > > > > > >> here: >>>>> > > > > > >> https://github.com/apache/iceberg/issues/16414 >>>>> > > > > > >> >>>>> > > > > > >> At a high level, the questions for the community are: >>>>> > > > > > >> 1. What should implementations write: Avro `int` (plain >>>>> > > > > > >> integer) or >>>>> > > > > Avro >>>>> > > > > > >> `date` (integer with a date logical type)? >>>>> > > > > > >> 2. Should implementations be required to read both forms, or >>>>> > > > > > >> just >>>>> > > > > > >> encouraged to? >>>>> > > > > > >> 3. Should the spec's transform result type table be updated >>>>> > > > > > >> from >>>>> > > > > `int` to >>>>> > > > > > >> `date`? >>>>> > > > > > >> >>>>> > > > > > >> I'd love to hear your thoughts. Thanks! >>>>> > > > > > >> >>>>> > > > > > >> Best, >>>>> > > > > > >> Kevin Liu >>>>> > > > > > >> >>>>> > > > > > > >>>>> > > > > > >>>>> > > > > >>>>> > > > >>>>> >
