+1 for using file sequence number. This work has been discussed for a long time but never got picked up, would be great if someone can drive it to completion.
-Jack On Wed, Apr 26, 2023 at 12:03 PM Anton Okolnychyi <aokolnyc...@apple.com.invalid> wrote: > Will a clock skew cause any issues w.r.t. relying on the snapshot commit > time? I think we allow a mismatch up to a minute in TableMetadata. > > We also planned to expose file sequence number (different from data > sequence number). I believe you could lookup snapshot using that info. > > https://iceberg.apache.org/spec/#manifest-entry-fields > > - Anton > > On Apr 26, 2023, at 11:52 AM, Steven Wu <stevenz...@gmail.com> wrote: > > piggyback on this thread since we are discussing exposing more metadata in > ContentFile or FileScanTask. Flink source watermark alignment can > potentially leverage the snapshot timestamp (when data files are > committed/appended to the table). Is it reasonable to expose some snapshot > metadata in the FileScanTask? > > This can help the Flink job to ensure two (or more) sources are proceeding > at similar paces. Some use cases may require column stats (min-max values) > for the watermark alignment. Some use cases can leverage snapshot > timestamps for the alignment purpose. > > On Wed, Apr 26, 2023 at 11:15 AM Anton Okolnychyi < > aokolnyc...@apple.com.invalid> wrote: > >> My initial thinking is that exposing sequence numbers on ContentFile is >> preferable (we would get it for free in scan tasks). That said, I’ll need >> to see how complicated the implementation would be. Exposing it on >> ContentScanTask is a viable alternative. However, we already have a >> precedent for assigning specId in InheritableMetadata. >> >> - Anton >> >> On Apr 26, 2023, at 10:41 AM, Ryan Blue <b...@tabular.io> wrote: >> >> Exposing sequence number makes sense for use cases like this. I also like >> the idea of exposing it through FileScanTask. That might be easier than >> trying to add it to ContentFile. >> >> Anton, what do you think about adding it to FileScanTask? >> >> On Wed, Apr 26, 2023 at 7:50 AM Anton Okolnychyi < >> aokolnyc...@apple.com.invalid> wrote: >> >>> It is actually my bad not following up on that after #5913 and #6002. >>> I’ll take a look at #5760 referenced below by the end of this week. >>> >>> The plan was to expose sequence numbers on ContentFile. It is needed in >>> a number of use cases. >>> >>> - Anton >>> >>> On Apr 26, 2023, at 4:55 AM, Gabor Kaszab <gaborkas...@apache.org> >>> wrote: >>> >>> Hey Iceberg Community, >>> >>> I know there has been a discussion previously about exposing the >>> sequence number on a ContentFile level, but if I'm not mistaken that >>> conversation didn't end with a consensus. I found some relevant PRs that >>> has been open for a while: >>> https://github.com/apache/iceberg/pull/5760 >>> https://github.com/apache/iceberg/pull/4769 (merged into the above PR) >>> >>> The reason I bring this topic up is that we started investigating >>> recently how to add read support for equality deletes to Impala. >>> Apparently, implementation-wise we could save a lot of hassle if sequence >>> numbers were exposed on a file level through the API, preferably somewhere >>> around calling planFiles(). We could then have a virtual 'SEQUENCE_NUMBER' >>> when scanning the data and delete files (separate scanners) and could >>> easily filter the rows in the JOIN node that joins the rows from the data >>> files with the ones from the delete files. (wouldn't go into more depth atm) >>> >>> With this mail I'd like to revive this conversation with the hope of >>> eventually coming to a solution that satisfies all participants. I've been >>> thinking of implementation choices we have to somehow provide sequence >>> numbers for the files: >>> - Extending ContentFile with sequence number: I checked the above PRs >>> and IIUC the issue with this approach is that ContentFile is meant to be >>> immutable and by the time they are created we don't have sequence numbers >>> to populate the ContentFile object. >>> - Extend FileScanTask with the file-level sequence numbers so after >>> calling planFiles() we could retrieve these numbers via a new API call on >>> the FileScanTask. >>> >>> There might be many other ways to implement this and I'd love to hear >>> what people think and would be great to find a way that would help us out >>> on Impala. >>> >>> Cheers, >>> Gabor >>> >>> >>> >>> >> >> -- >> Ryan Blue >> Tabular >> >> >> >
