Hi Gamber, Thanks for the proposal! Impala isn’t unique in needing this—I've seen similar requirements from other engines.
As others pointed out, using the “tableExists” endpoint seems like a workaround. I don't consider it a permanent way forward. We could address this by either modifying the current load table endpoint or introducing a new one, but ideally, we should avoid adding endpoints for every specific need. With that, partial metadata loading seems like a strong approach here, we will need certain agreement though. I'd suggest the community consider the use cases seriously. We need a way forward. I’m also not too concerned about using metadata file paths to verify the latest table version; clients can simply extract metadata filenames, which include the UUID. Yufei On Tue, Nov 12, 2024 at 7:46 AM Jean-Baptiste Onofré <j...@nanthrax.net> wrote: > Hi Fokko > > I like the idea, but I think it's more a workaround and could be > confusing for users :) > > Regards > JB > > On Tue, Nov 12, 2024 at 2:53 PM Fokko Driesprong <fo...@apache.org> wrote: > > > > Hey Gabor, > > > > Thanks for raising this. While reading this, my first thought is to > leverage the `tableExists` operation: > > > https://github.com/apache/iceberg/blob/e3f39972863f891481ad9f5a559ffef093976bd7/open-api/rest-catalog-open-api.yaml#L1129-L1160 > > > > This doesn't return anything today, but we could return a payload to the > latest metadata.json. > > > > Looking forward to what others think. > > > > Kind regards, > > Fokko > > > > > > > > > > Op di 12 nov 2024 om 14:33 schreef Shani Elharrar > <sh...@upsolver.com.invalid>: > >> > >> I recommend option (b), provided there is no partial metadata loading. > We implemented option (b) internally to facilitate partial metadata > loading, as we have tables with hundreds of thousands of snapshots. This > results in metadata that occupies approximately 500 MB in memory (excluding > the JsonNodes), which is a significant load for some of our services. > >> > >> Shani. > >> > >> On 12 Nov 2024, at 14:12, Gabor Kaszab <gaborkas...@apache.org> wrote: > >> > >> Hey Iceberg Community, > >> > >> Background: > >> Impala is designed in a way to cache the Iceberg table metadata > (BaseTable objects in practice) for faster access. Currently, Impala is > tightly coupled with HMS and in turn with the HiveCatalog, and in order to > keep the cached table objects up-to-date there is a notification mechanism > driven by HMS to notify Impala about any changes in the table metadata. > >> The Impala community is actively looking for ways to decouple HMS from > Impala and provide a way to use Impala without the need for HMS, and get > the Iceberg table metadata from other catalog Implementations mainly > focusing now on REST catalogs. > >> > >> Problem to solve: > >> We identified a particular missing functionality in the current REST > spec: For engines that cache table metadata currently there is no way to > check if that table metadata is up-to-date or not, and whether the engine > should reload the metadata for that table or not without getting a whole > table object from the catalog. For this I think the REST catalog (but in > fact I think this could apply to any other catalogs) should be able to > answer a question like: > >> "Hi Catalog, I have this version of this table, is it up-to-date?" > >> > >> Proposal: > >> I've been following the discussion about partial metadata loading that > could be also used to answer the above question, but I have the impression > now that the conversation stopped making any progress. > >> So instead of waiting for partial metadata loading I propose to have an > addition to the REST spec now to answer the question I raised above: > >> > >> a) boolean isLatest(TableIdentifier ident, String metadataLocation); > >> b) String metadataLocation(TableIdentifier ident); > >> > >> Any of the above 2 approaches could help engines to decide if they have > to invalidate/reload particular table metadata in the cache. I personally > would go for option a) but would be open to hear other opinions. > >> > >> I'd like to know if the community could support me extending the REST > spec with any of the 2 options. > >> > >> Regards, > >> Gabor > >> > >> >
