mbutrovich commented on code in PR #171:
URL: https://github.com/apache/datafusion-site/pull/171#discussion_r3204013232
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content/blog/2026-05-07-datafusion-comet-0.16.0.md:
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+---
+layout: post
+title: Apache DataFusion Comet 0.16.0 Release
+date: 2026-05-07
+author: pmc
+categories: [subprojects]
+---
+
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+-->
+
+[TOC]
+
+The Apache DataFusion PMC is pleased to announce version 0.16.0 of the
[Comet](https://datafusion.apache.org/comet/) subproject.
+
+Comet is an accelerator for Apache Spark that translates Spark physical plans
to DataFusion physical plans for
+improved performance and efficiency without requiring any code changes.
+
+This release covers approximately three weeks of development work and is the
result of merging 115 PRs from 17
+contributors. See the [change log] for more information.
+
+[change log]:
https://github.com/apache/datafusion-comet/blob/main/dev/changelog/0.16.0.md
+
+## Expanded Spark 4 Support
+
+Spark 4 is a major theme of this release. Comet now ships first-class support
for both Spark 4.0.2 and
+Spark 4.1.1, with dedicated Maven profiles, shim sources, and CI matrices for
each.
+
+- **Spark 4.1.1**: New `spark-4.1` Maven profile and shim sources, with
Comet's PR test matrix and Spark SQL
+ test suites enabled against Spark 4.1.1. The default Maven profile has been
updated to Spark 4.1 / Scala 2.13
+ to reflect that this is now the primary development target.
+- **Shared 4.x shims**: Identical pieces of the Spark 4.0 and 4.1 shims have
been consolidated into a shared
+ `spark-4.x` source tree, reducing duplication as more 4.x minor versions
land.
+- **Spark 4.0 / JDK 21**: Added a Spark 4.0 / JDK 21 CI profile to validate
Comet on the JDK most users are
+ expected to deploy with Spark 4.
+
+### Adapting to Spark 4 Behavior Changes
+
+Spark 4 introduced a number of type, planner, and on-disk format changes
relative to Spark 3.x. Several
+correctness fixes this cycle bring Comet's behavior in line with these changes:
+
+- **`Variant` type (new in Spark 4.0)**: Spark 4.0 added a new `Variant` data
type for semi-structured
+ data. Comet does not yet read the shredded Variant on-disk format natively,
and delegates these scans
+ to Spark.
+- **String collation (new in Spark 4.0)**: Spark 4.0 added collation support
for `StringType`. Comet's
+ native operators do not yet implement non-default collations, so hash join
and sort-merge join reject
+ collated string join keys, and shuffle, sort, and aggregate fall back to
Spark when keys carry a
+ non-default collation.
+- **Wider `TimestampNTZType` usage**: Spark 4 uses `TimestampNTZType`
(timestamp without time zone) in
+ more places than 3.x — for example, in expression return types and as the
inferred type for some
+ literal forms. Comet adds support this cycle for cast to and from
`timestamp_ntz`, cast from string to
+ `timestamp_ntz`, and `unix_timestamp` over `TimestampNTZType` inputs.
+- **DSv2 scalar subquery pushdown
([SPARK-43402](https://issues.apache.org/jira/browse/SPARK-43402))**:
Review Comment:
We can remove scalar subquery pushdown based on the adaptivity suggestion
below.
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