Hello Walaa, Thanks for starting this discussion.
I think we should decouple at least the MV Spec from the proposal to change the current behavior of view resolution. We can continue having the discussion if the current view spec needs to be changed or not. Based on the decision at a later point if required we can update the view resolution rule. Thanks, Rishabh On Mon, Apr 28, 2025 at 3:22 PM Walaa Eldin Moustafa <wa.moust...@gmail.com> wrote: > Correction of typo: both engines seem to set default-catalog to the view > catalog if it is defined, or to null if the view catalog is not defined. > > On Mon, Apr 28, 2025 at 3:06 PM Walaa Eldin Moustafa < > wa.moust...@gmail.com> wrote: > >> Hi Dan, >> >> Thanks again for your response. >> >> I agree that catalog renaming is an environmental event, but it's a real >> one that happens frequently in practice. >> Saying that the Iceberg spec cannot accommodate something as common as >> catalog renaming feels very restrictive, and could make the spec less >> practical, even unusable, for real-world deployments. >> I’m sharing this from the perspective of a large data lake environment >> where views are heavily deployed and operationalized. >> >> Further, it's worth noting that the table spec is resilient to catalog >> renaming, but the view spec is not. If we have an opportunity to make the >> view spec similarly resilient, I wonder why not? >> Both specifications are deterministic in their definition, but one is >> more fragile to environmental changes than the other. Improving resilience >> does not sacrifice determinism. It simply makes views safer and more >> portable over time. >> >> Separately, given that there is no SQL construct today to explicitly set >> default-catalog at creation time, what is the intuition behind how engines >> like Spark and Trino currently assign default-catalog? >> Today, both engines seem to set default-catalog to null if the view >> catalog is defined, or to the view catalog if not. >> What was the intended thought process behind this behavior? >> >> Thanks, >> Walaa >> >> On Mon, Apr 28, 2025 at 1:33 PM Daniel Weeks <dwe...@apache.org> wrote: >> >>> Walaa, >>> >>> > tables inside views remain reachable after a catalog rename >>> >>> This problem stems from the exact environmental/configuration issue that >>> we should not be trying to address. I don't think we would expect >>> references to survive a catalog rename. That's not something covered by >>> the spec and needs to be handled separately as a platform-level migration >>> specific to the affected environment. >>> >>> The identifier resolution logic is clear and deterministic. It should >>> not matter whether an engine resolves and encodes the default-catalog or >>> leaves it to the resolution rules. >>> >>> The issue isn't with how the spec is defined, but rather view behavior >>> when you start altering the environment around it, which isn't something we >>> should be trying to define here. >>> >>> -Dan >>> >>> On Mon, Apr 28, 2025 at 12:17 PM Walaa Eldin Moustafa < >>> wa.moust...@gmail.com> wrote: >>> >>>> Hi Dan, >>>> >>>> Thanks for chiming in. >>>> >>>> I believe the issues we’re seeing now go beyond just catalog naming >>>> consistency. The behavior around default-catalog itself introduces >>>> resolution inconsistencies even when catalog names are consistent. >>>> For example: >>>> >>>> * When default-catalog is set to null, tables inside views remain >>>> reachable after a catalog rename. But if it is set to a non-null value, >>>> table references will break. >>>> >>>> * default-catalog causes table references inside views to be early >>>> bound (i.e., bound at view creation time, especially when using a non-null >>>> value), while table references inside standalone queries are late bound >>>> (bound at query time). This creates inconsistencies when resolving the same >>>> table name inside and outside views, even within the same job. >>>> >>>> * It causes Spark's and Trino behavior to drift from the spec. There is >>>> no way to fully align Spark's behavior without making invasive changes to >>>> the Spark SQL grammar and the View DataSource API (specifically on the >>>> CREATE side). This challenge would extend to other engines too. Both Spark >>>> and Trino set this field based on a heuristic in today's implementation. >>>> >>>> * With view nesting (views depending on views), these inconsistencies >>>> amplify further, forcing users and engines to reason about catalog >>>> resolution at every level in the view tree. >>>> >>>> * It will be difficult to migrate Hive views to Iceberg with that >>>> model. Migrated Hive views will have to unfollow that spec. >>>> >>>> How would you suggest approaching the engine-level changes required to >>>> support the current default-catalog field? >>>> Also, do you believe the Spark and Trino communities would align around >>>> having table resolution behave inconsistently between queries and views, or >>>> inconsistency between Iceberg and other types of views? >>>> >>>> Thanks, >>>> Walaa >>>> >>>> >>>> On Mon, Apr 28, 2025 at 11:34 AM Daniel Weeks <dwe...@apache.org> >>>> wrote: >>>> >>>>> I would agree with Jan's summary of why 'default-catalog' was >>>>> introduced, but I think we need to step back and align on what we are >>>>> really attempting to support in the spec. >>>>> >>>>> The issues we're discussing largely stem from using multiple engines >>>>> with cross catalog references and configurations where catalog names are >>>>> not aligned. If we have multiple engines that all have the same catalog >>>>> names/configurations, the current spec implementation is well defined for >>>>> table resolution even across catalogs. The 'default-catalog' (and >>>>> namespace equivalent) was intended to address the resolution within the >>>>> context of the sql text, not to address catalog/naming inconsistencies. >>>>> >>>>> I feel like we're trying to adapt the original intent to address the >>>>> catalog naming/configuration and would argue that we shouldn't attempt to >>>>> do that as part of the spec. Inconsistently named catalogs are a reality, >>>>> but we should consider that a configuration/environmental issue, not >>>>> something to solve for in the spec. >>>>> >>>>> We should support and advocate for consistency in catalog naming and >>>>> define the spec along those lines. The fact is that with all of the >>>>> recent >>>>> work that's gone into making catalogs pluggable, it makes more sense to >>>>> just register catalog configuration with consistent names (even if you >>>>> have >>>>> to duplicate the configuration for supporting existing readers/writers). >>>>> I >>>>> think it's better to provide a path toward consistency than to normalize >>>>> complicated schemes to workaround the issues caused by >>>>> environmental/configuration inconsistencies. >>>>> >>>>> If the goal is to create clever ways to hack the late binding >>>>> resolution to swap in different catalogs or make references contextual, I >>>>> feel like that is something we should strongly discourage as it leads to >>>>> confusion about what is resolved as part of the query. >>>>> >>>>> At this point, I don't see a good argument to add >>>>> additional configuration or change the resolution behaviors. >>>>> >>>>> -Dan >>>>> >>>>> >>>>> >>>>> On Mon, Apr 28, 2025 at 12:40 AM Jan Kaul <jank...@mailbox.org.invalid> >>>>> wrote: >>>>> >>>>>> I think the intention with the "default-catalog" was that every query >>>>>> engine uses it to store its session default catalog at the time of >>>>>> creating >>>>>> the view. This way the view could be reused in another session. The idea >>>>>> was not to introduce an additional SQL syntax to set the default-catalog. >>>>>> >>>>>> Generally we have different environments we want to support with the >>>>>> view spec: >>>>>> >>>>>> 1. Consistent catalog naming >>>>>> >>>>>> When the environment supports it, using consistent catalog names can >>>>>> have a great benefit for multi-catalog, multi-engine setups. With >>>>>> consistent catalog names, using the "default-catalog" field works without >>>>>> any issues. >>>>>> >>>>>> 2. Inconsistent catalog naming >>>>>> >>>>>> This can be the case when different query engines refer to the same >>>>>> physical catalog by different names. This often happens because different >>>>>> query engines use different strategies to setup the catalogs. If catalogs >>>>>> have inconsistent naming, using the "default-catalog" field does not work >>>>>> because it is not guaranteed that the catalog name can be resolved with >>>>>> another engine. Using the "view catalog" as a fallback is a better >>>>>> solution >>>>>> for this use case, as it avoids catalog names altogether. It is however >>>>>> limited to table references in the same catalog. >>>>>> >>>>>> >>>>>> What do you think of introducing a view property that specifies if >>>>>> the "default-catalog" or the "view catalog" should be used? This way, you >>>>>> could use the "default-catalog" in environments where you can guarantee >>>>>> consistent naming, but you would be able to directly fallback to the >>>>>> "view-catalog" when you don't have consistent naming. The query engines >>>>>> could set the default for this view property at creation time. Spark for >>>>>> example could set it to automatically use the "view catalog". >>>>>> >>>>>> Thanks >>>>>> >>>>>> Jan >>>>>> >>>>>> >>>>>> On 4/26/25 05:33, Walaa Eldin Moustafa wrote: >>>>>> >>>>>> To help folks catch up on the latest discussions and interpretation >>>>>> of the spec, I have summarized everything we discussed so far at the top >>>>>> of >>>>>> the proposal document (here >>>>>> <https://docs.google.com/document/d/1-I2v_OqBgJi_8HVaeH1u2jowghmXoB8XaJLzPBa_Hg8/edit?tab=t.0>). >>>>>> I have slightly updated the proposal to be in sync with the new >>>>>> interpretation to avoid confusion. In summary: >>>>>> >>>>>> * Remove default-catalog and default-namespace fields from the view >>>>>> spec completely. >>>>>> >>>>>> * Hence, we do not attempt to define separate view-level default >>>>>> catalogs or namespaces. >>>>>> >>>>>> Instead: >>>>>> >>>>>> * If a table identifier inside a view lacks a catalog qualifier, >>>>>> engines should resolve it using the current engine catalog at query time. >>>>>> >>>>>> * Reference table identifiers in the metadata exactly as they appear >>>>>> in the view SQL text. >>>>>> >>>>>> * If an identifier lacks the catalog part at creation, it should >>>>>> still lack a catalog in the stored metadata. >>>>>> >>>>>> * Store UUIDs alongside table identifiers whenever possible. >>>>>> >>>>>> Thanks, >>>>>> Walaa. >>>>>> >>>>>> >>>>>> On Fri, Apr 25, 2025 at 5:18 PM Walaa Eldin Moustafa < >>>>>> wa.moust...@gmail.com> wrote: >>>>>> >>>>>>> Thanks for the contribution Benny! +1 to the confusion the fallback >>>>>>> creates. Also just to be clear, at this point and after clarifying the >>>>>>> current spec intentions, I am convinced that we should remove the >>>>>>> default >>>>>>> catalog and default namespace fields altogether. >>>>>>> >>>>>>> Thanks, >>>>>>> Walaa. >>>>>>> >>>>>>> On Fri, Apr 25, 2025 at 5:13 PM Benny Chow <btc...@gmail.com> wrote: >>>>>>> >>>>>>>> I'd like to contribute my opinions on this: >>>>>>>> >>>>>>>> - I don't particularly like the current behavior of "default to the >>>>>>>> view's catalog when default-catalog is not set". Fundamentally, I >>>>>>>> believe >>>>>>>> the intent of default-catalog and default-namespace is there to help >>>>>>>> users >>>>>>>> write more concise SQL. >>>>>>>> - spark session catalog is engine specific and I don't think we >>>>>>>> should design something that says first use this catalog, then that >>>>>>>> catalog.. or that catalog. For example, resolving identifiers using >>>>>>>> default-catalog -> view's catalog -> session catalog is not good. >>>>>>>> - We gotta support non-Iceberg tables otherwise I see no value in >>>>>>>> putting views in the catalog to share with other engines >>>>>>>> - Interoperability between different engine types is very hard due >>>>>>>> to dialect issues... so I think we should focus on supporting different >>>>>>>> clusters of the same engine type on a shared catalog. For example, AI >>>>>>>> and >>>>>>>> BI clusters on Spark sharing the same views in a REST catalog. >>>>>>>> >>>>>>>> Coincidentally, I think the ultimate solution is along the lines of >>>>>>>> something Russell proposed last year: >>>>>>>> >>>>>>>> https://lists.apache.org/thread/hoskfx8y3kvrcww52l4w9dxghp3pnlm7 >>>>>>>> >>>>>>>> We've been looking at this interoperable identifier problem through >>>>>>>> the lens of catalog resolution but maybe the right approach is really >>>>>>>> about >>>>>>>> templating. >>>>>>>> >>>>>>>> I would extend Russell's idea to allow identifiers in a view to >>>>>>>> span catalogs to support non-Iceberg tables. Also, the >>>>>>>> default-catalog >>>>>>>> property could be templated as well. >>>>>>>> >>>>>>>> Thoughts? >>>>>>>> Benny >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> On Fri, Apr 25, 2025 at 4:02 PM Walaa Eldin Moustafa < >>>>>>>> wa.moust...@gmail.com> wrote: >>>>>>>> >>>>>>>>> Thanks Steven! How do you recommend making Spark implementation >>>>>>>>> conform to the spec? Do we need Spark SQL extensions and/or Spark >>>>>>>>> catalog >>>>>>>>> APIs for that? >>>>>>>>> >>>>>>>>> How do you recommend reconciling the inconsistencies I shared >>>>>>>>> regarding many resolution methods not consistently being followed in >>>>>>>>> different scenarios (view vs child table resolution, query vs view >>>>>>>>> resolution)? Note these occur when the default catalog is set to a >>>>>>>>> non-null >>>>>>>>> value. If it helps, I can share concrete examples. >>>>>>>>> >>>>>>>>> Thanks, >>>>>>>>> Walaa. >>>>>>>>> >>>>>>>>> On Fri, Apr 25, 2025 at 3:52 PM Steven Wu <stevenz...@gmail.com> >>>>>>>>> wrote: >>>>>>>>> >>>>>>>>>> The core issue is on the fall back behavior when >>>>>>>>>> `default-catalog` is >>>>>>>>>> not defined. Current view spec says the fallback should be the >>>>>>>>>> catalog >>>>>>>>>> where the view is defined. It doesn't really matter what the >>>>>>>>>> catalog >>>>>>>>>> is named (catalogX) by the read engine. >>>>>>>>>> - If a view refers to the tables in the same catalog, this is a >>>>>>>>>> non-ambiguous and reasonable fallback behavior. >>>>>>>>>> - If a view refers to tables from another catalog, catalog names >>>>>>>>>> should be included in the reference name already. So no ambiguity >>>>>>>>>> there either. >>>>>>>>>> >>>>>>>>>> Potential inconsistent naming of catalog is a separate problem, >>>>>>>>>> which >>>>>>>>>> Iceberg view spec probably cannot solve. We can only recommend >>>>>>>>>> that >>>>>>>>>> catalog should be named consistently across usage for better >>>>>>>>>> interoperability on name references. >>>>>>>>>> >>>>>>>>>> This proposal is to change the fallback behavior to engine's >>>>>>>>>> session >>>>>>>>>> default catalog. I am not sure it is better than the current >>>>>>>>>> fallback >>>>>>>>>> behavior. >>>>>>>>>> >>>>>>>>>> > Today’s Spark behavior explicitly differs from this idea. Spark >>>>>>>>>> resolves table identifiers during view creation using the session’s >>>>>>>>>> default >>>>>>>>>> catalog, not a supplied `default-catalog`. >>>>>>>>>> >>>>>>>>>> I would argue that is a Spark implementation issue for not >>>>>>>>>> conforming >>>>>>>>>> to the spec. >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> On Fri, Apr 25, 2025 at 1:17 PM Walaa Eldin Moustafa >>>>>>>>>> <wa.moust...@gmail.com> wrote: >>>>>>>>>> > >>>>>>>>>> > Hi Jan, >>>>>>>>>> > >>>>>>>>>> > Thanks again for continuing the discussion. I want to highlight >>>>>>>>>> a few fundamental issues around the interpretation of >>>>>>>>>> default-catalog: >>>>>>>>>> > >>>>>>>>>> > Here is the real catch: >>>>>>>>>> > >>>>>>>>>> > * default-catalog cannot logically be defined at view creation >>>>>>>>>> time. It would be circular: the view needs to exist before its >>>>>>>>>> metadata >>>>>>>>>> (and hence default-catalog) can exist. This is visible in Spark’s >>>>>>>>>> implementation, where `default-catalog` is not used. >>>>>>>>>> > >>>>>>>>>> > * Introducing a creation-time default-catalog setting would >>>>>>>>>> require extending SQL syntax and engine APIs to promote it to a >>>>>>>>>> first-class >>>>>>>>>> view concept. This would be intrusive, non-intuitive, and >>>>>>>>>> realistically >>>>>>>>>> very difficult to standardize across engines. >>>>>>>>>> > >>>>>>>>>> > * Today’s Spark behavior explicitly differs from this idea. >>>>>>>>>> Spark resolves table identifiers during view creation using the >>>>>>>>>> session’s >>>>>>>>>> default catalog, not a supplied `default-catalog`. >>>>>>>>>> > >>>>>>>>>> > * Hypothetically even if we patched in a creation-time >>>>>>>>>> default-catalog, it would create an inconsistent binding model >>>>>>>>>> between >>>>>>>>>> tables vs views (early vs late), and between tables in views and in >>>>>>>>>> queries >>>>>>>>>> (again early vs late). For example, views and tables in queries can >>>>>>>>>> withstand default catalog renames, but tables cannot when they are >>>>>>>>>> used >>>>>>>>>> inside views -- it even applies to views inside views, which makes >>>>>>>>>> this >>>>>>>>>> very hard to reason about considering nesting. >>>>>>>>>> > >>>>>>>>>> > Thanks, >>>>>>>>>> > Walaa >>>>>>>>>> > >>>>>>>>>> > On Fri, Apr 25, 2025 at 7:00 AM Jan Kaul >>>>>>>>>> <jank...@mailbox.org.invalid> <jank...@mailbox.org.invalid> >>>>>>>>>> wrote: >>>>>>>>>> >> >>>>>>>>>> >> @Walaa: >>>>>>>>>> >> >>>>>>>>>> >> I would argue that when you run a CREATE VIEW statement the >>>>>>>>>> query engine knowns which catalog the view is being created in. So >>>>>>>>>> even >>>>>>>>>> though we typically use late binding to resolve the view catalog at >>>>>>>>>> query >>>>>>>>>> time, it can also be used at creation time. >>>>>>>>>> >> >>>>>>>>>> >> The query engine would need to keep track of the "view >>>>>>>>>> catalog" where the view is going to be created in. It can use that >>>>>>>>>> catalog >>>>>>>>>> to resolve partial table identifiers if "default-catalog" is not set. >>>>>>>>>> >> >>>>>>>>>> >> It can lead to some unintuitive behavior, where partial >>>>>>>>>> identifiers in the view query resolve to a different catalog >>>>>>>>>> compared to >>>>>>>>>> using them outside of a view. >>>>>>>>>> >> >>>>>>>>>> >> 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", which is the view's catalog. >>>>>>>>>> >> >>>>>>>>>> >> Thanks, >>>>>>>>>> >> >>>>>>>>>> >> Jan >>>>>>>>>> >> >>>>>>>>>> >> On 4/25/25 04:05, Manu Zhang wrote: >>>>>>>>>> >>> >>>>>>>>>> >>> 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? >>>>>>>>>> >> >>>>>>>>>> >> I don't think this is related to view spec. How do we validate >>>>>>>>>> that a table exists without a default catalog, or do we always use >>>>>>>>>> the >>>>>>>>>> current session catalog? >>>>>>>>>> >> >>>>>>>>>> >> Thanks, >>>>>>>>>> >> Manu >>>>>>>>>> >> >>>>>>>>>> >> On Fri, Apr 25, 2025 at 5:59 AM Walaa Eldin Moustafa < >>>>>>>>>> wa.moust...@gmail.com> wrote: >>>>>>>>>> >>> >>>>>>>>>> >>> 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> <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. >>>>>>>>>> >>>>>>>>>
