[GitHub] [hudi] YannByron commented on a diff in pull request #5436: [RFC-51] [HUDI-3478] Change Data Capture RFC

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YannByron commented on code in PR #5436:
URL: https://github.com/apache/hudi/pull/5436#discussion_r882254049


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rfc/rfc-51/rfc-51.md:
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+
+# RFC-50: Hudi CDC
+
+# Proposers
+
+- @Yann Byron
+
+# Approvers
+
+- @Raymond
+
+# Statue
+JIRA: [https://issues.apache.org/jira/browse/HUDI-3478](https://issues.apache.org/jira/browse/HUDI-3478)
+
+# Hudi Supports Change-Data-Capture
+
+## Abstract
+
+We want to introduce the Change-Data-Capture(CDC) capacity that make hudi can produce the changeing data by which we can know how the records is changed, to response the CDC cases.
+
+
+## Background
+
+In some use cases where hudi tables is used as streaing source, We want to be aware every records' changing in one commit exactly. In a certain commit or snapshot, which records are inserted, which records are deleted, and which records are updated. Even for the updated records, both the old value before updated and the new value after updated are needed.
+
+To implement this capacity, we have to upgrade the write and read parts. Let hudi can figure out the changing data when read. And in some cases, writing the extra data to help querying the changing data if necessary.
+
+## Scenario Definition
+
+Here use a simple case to explain the CDC.
+
+![](scenario-definition.jpg)
+
+Here we follow the debezium output format, there are four columns shown:
+- op: the operation of this record;
+- ts_ms: the timestamp;
+- source: source information such as the name of database and table. **Maybe we don't need this column in Hudi**;
+- before: the previous image before this operation;
+- after: the current image after this operation;
+
+`op` column has three enum values:
+- i: represent `insert`; when `op` is `i`, `before` is always null;
+- u: represent `update`; when `op` is `u`, both `before` and `after` don't be null;
+- d: represent `delete`; when `op` is `d`, `after` is always null;
+
+Notice:
+Here the illustration ignores all the metadata columns in `before` and `after` columns like `_hoodie_commit_time`.
+
+## Goals
+
+1. Support row-level CDC records generation and persistence;
+2. Support both MOR and COW tables;
+3. Support all the write operations;
+4. Support Spark DataFrame/SQL/Streaming Query;

Review Comment:
   The writing logic is for both flink and spark. Flink just needs to adapt the reading logic.
   But I'm not familiar with Flink. so can we involve flink developers to implement this?



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