xushiyan commented on code in PR #6256: URL: https://github.com/apache/hudi/pull/6256#discussion_r964188068
########## rfc/rfc-51/rfc-51.md: ########## @@ -148,20 +152,46 @@ hudi_cdc_table/ Under a partition directory, the `.log` file with `CDCBlock` above will keep the changing data we have to materialize. -There is an option to control what data is written to `CDCBlock`, that is `hoodie.table.cdc.supplemental.logging`. See the description of this config above. +#### Persisting CDC in MOR: Write-on-indexing vs Write-on-compaction + +2 design choices on when to persist CDC in MOR tables: + +Write-on-indexing allows CDC info to be persisted at the earliest, however, in case of Flink writer or Bucket +indexing, `op` (I/U/D) data is not available at indexing. + +Write-on-compaction can always persist CDC info and achieve standardization of implementation logic across engines, +however, some delays are added to the CDC query results. Based on the business requirements, Log Compaction (RFC-48) or +scheduling more frequent compaction can be used to minimize the latency. -Spark DataSource example: +The semantics we propose to establish are: when base files are written, the corresponding CDC data is also persisted. + +- For Spark + - inserts are written to base files: the CDC data `op=I` will be persisted + - updates/deletes that written to log files are compacted into base files: the CDC data `op=U|D` will be persisted +- For Flink + - inserts/updates/deletes that written to log files are compacted into base files: the CDC data `op=I|U|D` will be + persisted + +In summary, we propose CDC data to be persisted synchronously upon base files generation. It is therefore +write-on-indexing for Spark inserts (non-bucket index) and write-on-compaction for everything else. + +Note that it may also be necessary to provide capabilities for asynchronously persisting CDC data, in terms of a +separate table service like `ChangeTrackingService`, which can be scheduled to fine-tune the CDC-persisting timings. Review Comment: updated. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: commits-unsubscr...@hudi.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
