Au-Miner commented on code in PR #28294:
URL: https://github.com/apache/flink/pull/28294#discussion_r3360187912
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docs/content/docs/dev/table/tuning.md:
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@@ -431,12 +431,19 @@ Delta joins are continuously evolving, and supports the
following features curre
2. Support for **CDC** tables without **DELETE operations** as source tables.
3. Support for **projection** and **filter** operations between the source and
the delta join.
4. Support for **caching** within the delta join operator.
+5. Support for **cascaded delta joins** — eligible join nodes in a query are
sequentially converted into delta join nodes from source to sink.
+6. Support for **lookup join** after a delta join.
+7. Support for **non-deterministic functions** in projections and filters
between the delta join and downstream operators.
However, Delta Joins also have several **limitations**. Jobs containing any of
the following conditions cannot be optimized into a delta join:
1. The **index key** of the table must be included in the join’s **equivalence
conditions**.
2. Only **INNER JOIN** is currently supported.
3. The **downstream operator** must be able to handle **duplicate changes**,
such as a sink operating in **UPSERT mode** without `upsertMaterialize`.
-4. When consuming a **CDC stream**, the **join key** must be part of the
**primary key**.
-5. When consuming a **CDC stream**, all **filters** must be applied on the
**upsert key**.
-6. **Non-deterministic functions** are not allowed in filters or projections.
\ No newline at end of file
+4. When consuming a **CDC stream**, the **join key** must be part of the
**upsert key**<sup>[1]</sup>.
+5. When consuming a **CDC stream**, all **filters** must be applied on the
**upsert key**<sup>[1]</sup>.
+6. **Non-deterministic functions** are not allowed in projections or filters
between the source and the delta join.
+
+{{< hint info >}}
+[1] Flink supports defining a table-level **immutable columns** constraint to
enrich the upsert key, enabling delta join optimization in more scenarios. The
immutable columns constraint declares that certain columns, once set for a
given primary key, cannot be modified. The immutable columns are combined with
the primary key to form a new upsert key that is propagated to downstream
operators. This information is provided by the external storage system. [Apache
Fluss(Incubating)](https://fluss.apache.org/) is planning to support
table-level immutable columns constraint in the future.
Review Comment:
nits: [Apache Fluss(Incubating)] -> [Apache Fluss (Incubating)]
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