(datafusion-comet) 01/01: docs: add an FAQ page with an answer on vectorized Java/Scala UDFs (#6778)

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commit f9dd86d482d136426990186c2f1d42eef6a1ca59
Author: Andy Grove <ag...@apache.org>
AuthorDate: Thu Oct 8 15:49:12 2026 +0000

    docs: add an FAQ page with an answer on vectorized Java/Scala UDFs (#6778)
    
    * docs: add an FAQ page with an answer on vectorized Java/Scala UDFs
    
    The About section gets a Frequently Asked Questions page. Its first
    question is whether Comet plans an API for vectorized Java/Scala UDFs
    like the Rust UDF API. The answer gives what the prototype in #6697
    found: for simple functions the vectorized form saved about 3 ns per
    row once the code generator's overheads were removed, which did not
    justify the API's cost to users. It also says where a vectorized
    function could still pay off, and points to #6694 for those use cases.
    
    * docs: shorten the vectorized UDF FAQ answer
---
 docs/source/about/faq.md   | 37 +++++++++++++++++++++++++++++++++++++
 docs/source/about/index.md |  5 ++++-
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/docs/source/about/faq.md b/docs/source/about/faq.md
new file mode 100644
index 0000000000..f7313fac28
--- /dev/null
+++ b/docs/source/about/faq.md
@@ -0,0 +1,37 @@
+<!---
+  Licensed to the Apache Software Foundation (ASF) under one
+  or more contributor license agreements.  See the NOTICE file
+  distributed with this work for additional information
+  regarding copyright ownership.  The ASF licenses this file
+  to you under the Apache License, Version 2.0 (the
+  "License"); you may not use this file except in compliance
+  with the License.  You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing,
+  software distributed under the License is distributed on an
+  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+  KIND, either express or implied.  See the License for the
+  specific language governing permissions and limitations
+  under the License.
+-->
+
+# Frequently Asked Questions
+
+## Does Comet plan to add an API for vectorized Java/Scala UDFs similar to the Rust UDF API?
+
+Not at the moment. Comet already runs ordinary Scala and Java UDFs in its pipeline without code
+changes, compiling each call into a loop over a whole batch that the JVM optimizes well. See
+[Scala UDF and Java UDF Support](../user-guide/latest/scala_java_udfs.md).
+
+A prototype ([#6697](https://github.com/apache/datafusion-comet/pull/6697)) found that, once the code
+generator's overheads were reduced, a vectorized rewrite of a simple function such as `x + 1` saved
+only about 3 ns per row. That does not justify asking users to rewrite their functions against
+Comet's relocated Arrow classes and rebuild them for every Comet release, so the effort is going into
+the code generator instead.
+
+If you have a use case that a function of one row handles poorly, such as working on the UTF-8 bytes
+of strings or calling a library that processes whole batches, please describe it in
+[#6694](https://github.com/apache/datafusion-comet/issues/6694). For native speed, see the
+experimental [Rust UDF API](../user-guide/latest/rust_udfs.md).
diff --git a/docs/source/about/index.md b/docs/source/about/index.md
index c5bddb38d1..fc30f765c7 100644
--- a/docs/source/about/index.md
+++ b/docs/source/about/index.md
@@ -20,10 +20,12 @@ under the License.
 # About
 
 Background on the project: how Comet compares to similar accelerators, how releases
-are versioned, and links to the Apache Software Foundation resources behind it.
+are versioned, answers to common questions, and links to the Apache Software Foundation resources
+behind it.
 
 - [Comparison with Gluten](gluten_comparison.md) — how Comet differs from other Spark accelerators
 - [Versioning Policy](versioning_policy.md) — what our version numbers mean and our release cadence
+- [Frequently Asked Questions](faq.md) — answers to common questions about Comet's features and plans
 - [Blog Posts and Talks](blogs-and-talks.md) — external writing and conference talks about Comet
 - [ASF Links](../asf/index.md) — licensing, donations, security reporting, and the code of conduct
 
@@ -34,6 +36,7 @@ are versioned, and links to the Apache Software Foundation resources behind it.
 
 Comparison with Gluten <gluten_comparison>
 Versioning Policy <versioning_policy>
+Frequently Asked Questions <faq>
 Blog Posts and Talks <blogs-and-talks>
 ASF Links <../asf/index>
 ```


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