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if Hive Sync is enabled in the deltastreamer tool or datasource, the dataset is available in Hive as a couple of tables, that can now be read using HiveQL, Presto or SparkSQL. See here for more.

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When issuing an `upsert` operation on a dataset and the batch of records provided contains multiple entries for a given key, then all of them are reduced into a single final value by repeatedly calling payload class's preCombine() method . By default, we pick the record with the greatest value (determined by calling .compareTo()) giving latest-write-wins style semantics.

For an insert or bulk_insert operation, no such pre-combining is performed. Thus, if your input contains duplicates, the dataset would also contain duplicates. If you don't want duplicate records either issue an upsert or consider specifying option to de-duplicate input in either datasource or deltastreamer.

Can I implement my own logic for how input records are merged with record on storage

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GDPR has made deletes a must-have tool in everyone's data management toolbox. Hudi supports both soft and hard deletes. For details on how to actually perform them, see here.

How do I migrate my data to Hudi

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