Hi Andrei Thanks for starting this thread after our discussion during Lakehouse Day/CommunityOverCode in Glasgow.
I'm +1 to option B (labels as a read-only projection over tags). Tags already have definitions, allowed values, inheritance and reverse lookup, and both models are keyed by Iceberg field-id. A separate labels entity would give us two source of truth to reconcile, with no benefit imho. The tag work isn't merged yet, so it's cheap (good timing :)) to reserve what the consumer role needs. Postponing this later would be much more painful. I would keep the actual federation impl out of the first tag PR. About collisions, "native wins" is reasonable. Polaris is the asserting catalog at the point of access, so I'm fine with that rule. I have a few questions: - We have to be careful that tag-definition visibility (permission) doesn't leak through labels. Do we plan to see labels on loadTable/loadView relying on the table read privileges? Or do we want specific privileges for label/tag? - Resolving tags with inheritence on every loadTable can be significant for performence. What are your thoughts about that? Opt caching? - Do we want to have label emitted by default, or do you want to guate by catalog configuration (polaris.label.enabled=on)? Thanks! Regards JB On Sun, Oct 11, 2026 at 11:26 AM Andrei Tserakhau via dev < [email protected]> wrote: > Hi all, > > Now that the IRC "labels" field has merged in Iceberg Spec ([0]) and the > Polaris Tag work is close ([1]), I'd like to open a thread on how Polaris > should support labels. > > There are two ways Polaris could do labels: > > A) Labels as a separate entity - their own definitions/store, parallel to > Tags. > B) Labels as a projection over Tags - read-only IRC view / projection of > the existing tag model. > > I propose B. Tags already are the structured model: definitions, > assignments, allowed values, inheritance, reverse lookup. IRC labels are > designed as the flat read surface of such models (object-level key/values > plus per-field labels by field-id). A separate labels entity would > duplicate the tag model and create two sources of truth to reconcile; a > projection keeps one model with two surfaces, a structured authoring API > and an interoperable flat read field. Column identity already lines up: > Tags use the Iceberg field-id, and IRC labels fields are keyed by field-id. > > Given B, a Polaris catalog plays two roles: > > 1. Producer. Polaris resolves a target's effective tags (inheritance > applied, closest-wins) and projects them into IRC labels on > loadTable/loadView. The Tag API stays the authoring/management surface and > labels is the read projection for IRC compliant engines. > > 2. Consumer. When Polaris federates a foreign IRC catalog, it reads that > catalog's labels and stores them as tags owned by the source catalog: > read-only in Polaris and clearly marked as foreign. A Polaris user cannot > edit them (they change only when Polaris re-syncs from the source) and they > stay separate from Polaris's own natively-authored tags. That is how a > foreign catalog's metadata becomes usable in Polaris without pretending it > is local. > > Mostly I'd like the community read on whether projection-over-tags feels > right, and whether the producer/consumer split is worth keeping in mind in > the Tag design so the contract leaves room for it. Would like to hear if > this framing is wrong, or where a separate entity would actually serve > better. > > Thanks, > Andrei > > [0] IRC Labels spec PR - https://github.com/apache/iceberg/pull/15750 > [1] Tags discussion thread - > https://lists.apache.org/thread/28h8bvg3pwwmpob2p4gcrpfs1x5cgkmn >
