We never closed the loop on this :) I have one suggestion to keep the explanation format agnostic, please take a look! https://github.com/apache/iceberg/pull/16446#pullrequestreview-4472647904 I'm also happy to merge the PR as is. The most important part is to change the result type from `int` -> `date`
Best, Kevin Liu On Fri, May 22, 2026 at 9:00 PM Gang Wu <[email protected]> wrote: > 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 > >>>>> > > > > > >> > >>>>> > > > > > > > >>>>> > > > > > > >>>>> > > > > > >>>>> > > > > >>>>> > >
