Hi Jan, I think we still share the same understanding. Just to clarify: when I referred to late binding as “similar” to the proposal, I was acknowledging the distinction between view-level and table-level resolution. But as you noted, both follow a late binding model.
That said, this still raises an interesting question and a potential gap: if default-catalog is only defined at query time, how should resolution work during view creation? For example, if we want to validate that the tables referenced in the view exist, how can we do that when default-catalog isn't defined, since the view hasn't been created or loaded yet? Thanks, Walaa. On Thu, Apr 24, 2025 at 7:02 AM Jan Kaul <jank...@mailbox.org.invalid> wrote: > Yes, I have the same understanding. The view catalog is resolved at query > time. > > As you mentioned before, it's good to distinguish between the physical > catalog and it's reference used in SQL statements. The important part is > that the physical catalog of the view and the tables referenced in it's > definition stay consistent. You could create a view in a given physical > catalog by referring to it as "catalogA", as in your first point. If you > then, given a different setup, refer to the same physical catalog as > "catalogB" in another session/environment, the behavior should still work. > > I would however rephrase your last point. Late binding applies to the view > catalog name and by extension to all partial table references when no > "default-catalog" is present. Resolving the view catalog name at query time > is not opposed to storing the view metadata in a catalog. > > Or maybe I don't entirely understand what you mean. > > Thanks > > Jan > On 4/24/25 00:32, Walaa Eldin Moustafa wrote: > > Hi Jan, > > > The view is executed when it's being referenced in a SQL statement. That > statement contains the information for the query engine to resolve the > catalog of the view. > > If I’m understanding correctly, that means: > > * If the view is queried as SELECT * FROM catalogA.namespace.view, then > catalogA is considered the view’s catalog. > > * If the same view is later queried as SELECT * FROM > catalogB.namespace.view (after renaming catalogA to catalogB, and keeping > everything else the same), then catalogB becomes the view’s catalog. > > Is that interpretation correct? If so, it sounds to me like the catalog is > resolved at query time, based on how the view is referenced, not from any > stored metadata. That would imply some sort of a late binding behavior > (similar to the proposal), as opposed to using some catalog that "stores" > the view definition. > > Thanks, > Walaa > > On Tue, Apr 22, 2025 at 11:01 AM Jan Kaul <jank...@mailbox.org.invalid> > <jank...@mailbox.org.invalid> wrote: > >> Hi Walaa, >> >> Thanks for clarifying the aspects of non-determinism. Let me try to >> address your questions. >> >> 1. This is my interpretation of the current spec: The view is executed >> when it's being referenced in a SQL statement. That statement contains the >> information for the query engine to resolve the catalog of the view. The >> query engine then uses that information to fetch the view metadata from the >> catalog. It also needs to temporarily keep track of which catalog it used >> to fetch the view metadata. It can then use that information to resolve the >> table references in the views SQL definition in case no default catalog is >> specified. >> >> 2. The important part is that the catalog can be referenced at execution >> time. As long as that's the case I would assume the view can be created in >> any catalog. >> >> >> I think your point is really valuable because the current specification >> can lead to some unintuitive behavior. For example for the following >> statement: >> >> CREATE VIEW catalogA.sales.monthly_orders AS SELECT * from sales.orders; >> >> If the session default catalog is not "catalogA", the "sales.orders" in >> the view query would not be the same as just referencing "sales.orders" in >> a normal SQL statement. This is because without a "default-catalog", the >> catalog name of "sales.orders" would default to "catalogA". >> >> >> However, I like the current design of the view spec, because it has the >> "closure" property. Because of the fact that the "view catalog" has to be >> known when executing a view, all the information required to resolve the >> table identifiers is contained in the view metadata (and the "view >> catalog"). I think that if you make the identifier resolution dependent on >> external parameters, it hinders portability. >> >> Thanks, >> >> Jan >> On 4/22/25 18:36, Walaa Eldin Moustafa wrote: >> >> Hi Jan, >> >> Thanks for the thoughtful feedback. >> >> I think it’s important we clarify a key point before going deeper: >> >> Non-determinism is not caused by session fallback behavior—it’s a >> *fundamental >> limitation of using table identifiers* alone, regardless of whether we >> use the current rule, the proposed fallback to the session’s default >> catalog, or even early vs. late binding. >> >> The same fully qualified identifier (e.g., catalogA.namespace.table) can >> resolve to different objects depending solely on engine-specific routing >> logic or catalog aliases. So determinism isn’t guaranteed just because an >> identifier is "fully qualified." The only reliable anchor for identity is >> the UUID. That’s why the proposed use of UUIDs is not just a hardening >> strategy. It’s the actual fix for correctness. >> >> To move the conversation forward, could you help clarify two things in >> the context of the current spec: >> >> * Where in the metadata is the “view catalog” stored, so that an engine >> knows to fall back to it if default-catalog is null? >> >> * Are we even allowed to create views in the session's default catalog >> (i.e., without specifying a catalog) in the current Iceberg spec? >> >> These questions are important because if we can’t unambiguously recover >> the "view catalog" from metadata, then defaulting to it is problematic. And >> if views can't be created in the default catalog, then the fallback rule >> doesn’t generalize. >> >> Thanks, >> Walaa. >> >> On Tue, Apr 22, 2025 at 3:14 AM Jan Kaul <jank...@mailbox.org.invalid> >> <jank...@mailbox.org.invalid> wrote: >> >>> Hi Walaa, >>> >>> thank you for your proposal. If I understood correctly, you proposal is >>> composed of three parts: >>> >>> - session default catalog as fallback for "default-catalog" >>> >>> - session default namespace as fallback for "default-namepace" >>> >>> - Late binding + UUID validation >>> >>> I have some comments regarding these points. >>> >>> >>> 1. Session default catalog as fallback for "default-catalog" >>> >>> Introducing a behavior that depends on the current session setup is in >>> my opinion the definition of "non-determinism". You could be running the >>> same query-engine and catalog-setup on different days, with different >>> default session catalogs (which is rather common), and would be getting >>> different results. >>> >>> Whereas with the current behavior, the view always produces the same >>> results. The current behavior has some rough edges in very niche use cases >>> but I think is solid for most uses cases. >>> 2. Session default namespace as fallback for "default-namespace" >>> >>> Similar to the above. >>> 3. Late binding + UUID validation >>> >>> If I understand it correctly, the current implementation already uses >>> late binding. >>> >>> Generally, having UUID validation makes the setup more robust. Which is >>> great. However, having UUID validation still requires us to have a portable >>> table identifier specification. Even if we have the UUIDs of the referenced >>> tables from the view, there simply isn't an interface that let's us use >>> those UUIDs. The catalog interface is defined in terms of table identifiers. >>> >>> So we always require a working catalog setup and suiting table >>> identifiers to obtain the table metadata. We can use the UUIDs to verify if >>> we loaded the correct table. But this can only be done after we used some >>> identifier. Which means there is no way of using UUIDs without a >>> functioning catalog/identifier setup. >>> >>> >>> In conclusion, I prefer the current behavior for "default-catalog" >>> because it is more deterministic in my opinion. And I think the current >>> spec does a good job for multi-engine table identifier resolution. I see >>> the UUID validation more of an additional hardening strategy. >>> >>> Thanks >>> >>> Jan >>> On 4/21/25 17:38, Walaa Eldin Moustafa wrote: >>> >>> Thanks Renjie! >>> >>> The existing spec has some guidance on resolving catalogs on the fly >>> already (to address the case of view text with table identifiers missing >>> the catalog part). The guidance is to use the catalog where the view is >>> stored. But I find this rule hard to interpret or use. The catalog itself >>> is a logical construct—such as a federated catalog that delegates to >>> multiple physical backends (e.g., HMS and REST). In such cases, the catalog >>> (e.g., `my_catalog` in `my_catalog.namespace1.table1`) doesn’t physically >>> store the tables; it only routes requests to underlying stores. Therefore, >>> defaulting identifier resolution based on the catalog where the view is >>> "stored" doesn’t align with how catalogs actually behave in practice. >>> >>> Thanks, >>> Walaa. >>> >>> On Sun, Apr 20, 2025 at 11:17 PM Renjie Liu <liurenjie2...@gmail.com> >>> wrote: >>> >>>> Hi, Walaa: >>>> >>>> Thanks for the proposal. >>>> >>>> I've reviewed the doc, but in general I have some concerns with >>>> resolving catalog names on the fly with query engine defined catalog names. >>>> This introduces some flexibility at first glance, but also makes >>>> misconfiguration difficult to explain. >>>> >>>> But I agree with one part that we should store resolved table uuid in >>>> view metadata, as table/view renaming may introduce errors that's difficult >>>> to understand for user. >>>> >>>> On Sat, Apr 19, 2025 at 3:02 AM Walaa Eldin Moustafa < >>>> wa.moust...@gmail.com> wrote: >>>> >>>>> Hi Everyone, >>>>> >>>>> Looking forward to keeping up the momentum and closing out the MV spec >>>>> as well. I’m hoping we can proceed to a vote next week. >>>>> >>>>> Here is a summary in case that helps. The proposal outlines a strategy >>>>> for handling table identifiers in Iceberg view metadata, with the goal of >>>>> ensuring correctness, portability, and engine compatibility. It recommends >>>>> resolving table identifiers at read time (late binding) rather than >>>>> creation time, and introduces UUID-based validation to maintain identity >>>>> guarantees across engines, or sessions. It also revises how >>>>> default-catalog >>>>> and default-namespace are handled (defaulting both to the session context >>>>> if not explicitly set) to better align with engine behavior and improve >>>>> cross-engine interoperability. >>>>> >>>>> Please let me know your thoughts. >>>>> >>>>> Thanks, >>>>> Walaa. >>>>> >>>>> >>>>> >>>>> On Wed, Apr 16, 2025 at 2:03 PM Walaa Eldin Moustafa < >>>>> wa.moust...@gmail.com> wrote: >>>>> >>>>>> Thanks Eduard and Sung! I have addressed the comments. >>>>>> >>>>>> One key point to keep in mind is that catalog names in the spec refer >>>>>> to logical catalogs—i.e., the first part of a three-part identifier. >>>>>> These >>>>>> correspond to Spark's DataSourceV2 catalogs, Trino connectors, and >>>>>> similar >>>>>> constructs. This is a level of abstraction above physical catalogs, which >>>>>> are not referenced or used in the view spec. The reason is that table >>>>>> identifiers in the view definition/text itself refer to logical catalogs, >>>>>> not physical ones (since they interface directly with the engine and not >>>>>> a >>>>>> specific metastore). >>>>>> >>>>>> Thanks, >>>>>> Walaa. >>>>>> >>>>>> >>>>>> On Wed, Apr 16, 2025 at 6:15 AM Sung Yun <sungwy...@gmail.com> wrote: >>>>>> >>>>>>> Thank you Walaa for the proposal. I think view portability is a very >>>>>>> important topic for us to continue discussing as it relies on many >>>>>>> assumptions within the data ecosystem for it to function like you've >>>>>>> highlighted well in the document. >>>>>>> >>>>>>> I've added a few comments around how this may impact the permission >>>>>>> questions the engines will be asking, and whether that is the desired >>>>>>> behavior. >>>>>>> >>>>>>> Sung >>>>>>> >>>>>>> On Wed, Apr 16, 2025 at 7:32 AM Eduard Tudenhöfner < >>>>>>> etudenhoef...@apache.org> wrote: >>>>>>> >>>>>>>> Thanks Walaa for tackling this problem. I've added a few comments >>>>>>>> to get a better understanding of how this will look like in the actual >>>>>>>> implementation. >>>>>>>> >>>>>>>> Eduard >>>>>>>> >>>>>>>> On Tue, Apr 15, 2025 at 7:09 PM Walaa Eldin Moustafa < >>>>>>>> wa.moust...@gmail.com> wrote: >>>>>>>> >>>>>>>>> Hi Everyone, >>>>>>>>> >>>>>>>>> Starting this thread to resume our discussion on how to reference >>>>>>>>> table identifiers from Iceberg metadata, a key aspect of the view >>>>>>>>> specification, particularly in relation to the MV (materialized view) >>>>>>>>> extensions. >>>>>>>>> >>>>>>>>> I had the chance to speak offline with a few community members to >>>>>>>>> better understand how the current spec is being interpreted. Those >>>>>>>>> conversations served as inputs to a new proposal on how table >>>>>>>>> identifier >>>>>>>>> references could be represented in metadata. >>>>>>>>> >>>>>>>>> You can find the proposal here [1]. I look forward to your >>>>>>>>> feedback and working together to move this forward so we can finalize >>>>>>>>> the >>>>>>>>> MV spec as well. >>>>>>>>> >>>>>>>>> [1] >>>>>>>>> https://docs.google.com/document/d/1-I2v_OqBgJi_8HVaeH1u2jowghmXoB8XaJLzPBa_Hg8/edit?tab=t.0 >>>>>>>>> >>>>>>>>> Thanks, >>>>>>>>> Walaa. >>>>>>>>> >>>>>>>>
