[GitHub] [iceberg] dixingxing0 edited a comment on pull request #2109: Flink: store watermark as iceberg table's property

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dixingxing0 edited a comment on pull request #2109:
URL: https://github.com/apache/iceberg/pull/2109#issuecomment-762686286


   > @dixingxing0 can you describe the motivation of checkpointing the watermarks in Flink state?
   > 
   > Ryan described our use of watermarks in snapshot metadata. They are used to indicate the data completeness on the ingestion path so that downstream batch consumer jobs can be triggered when data is complete for a window (like hourly).
   
   Thanks @stevenzwu, about the watermark state, i am just according to the current restore behavior:
   ```java
         NavigableMap<Long, byte[]> uncommittedDataFiles = Maps
             .newTreeMap(checkpointsState.get().iterator().next())
             .tailMap(maxCommittedCheckpointId, false);
         if (!uncommittedDataFiles.isEmpty()) {
           **// Committed all uncommitted data files from the old flink job to iceberg table.**
           long maxUncommittedCheckpointId = uncommittedDataFiles.lastKey();
           commitUpToCheckpoint(uncommittedDataFiles, restoredFlinkJobId, maxUncommittedCheckpointId);
         }
   ```
   Since flink will commit last uncommitted checkpoint, i think we should also store the right watermark for that checkpoint.
   
   Our use case is exactly same as you and @rdblue described, except we don't have multi writers 😄 .


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