Comet 0.2.0 blog post (#23)

* add Comet 0.2.0 blog post

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_posts/2024-08-28-datafusion-comet-0.2.0.md

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+---
+layout: post
+title: "Apache DataFusion Comet 0.2.0 Release"
+date: "2024-08-28 00:00:00"
+author: pmc
+categories: [subprojects]
+---
+
+<!--
+{% comment %}
+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.
+{% endcomment %}
+-->
+
+The Apache DataFusion PMC is pleased to announce version 0.2.0 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.
+
+Comet runs on commodity hardware and aims to provide 100% compatibility with Apache Spark. Any operators or
+expressions that are not fully compatible will fall back to Spark unless explicitly enabled by the user. Refer
+to the [compatibility guide] for more information.
+
+[compatibility guide]: https://datafusion.apache.org/comet/user-guide/compatibility.html
+
+This release covers approximately four weeks of development work and is the result of merging 87 PRs from 14 
+contributors. See the [change log] for more information.
+
+[change log]: https://github.com/apache/datafusion-comet/blob/main/dev/changelog/0.2.0.md
+
+## Release Highlights
+
+### Docker Images
+
+Docker images are now available from the [GitHub Container Registry].
+
+[GitHub Container Registry]: https://github.com/apache/datafusion-comet/pkgs/container/datafusion-comet/265110454?tag=spark-3.4-scala-2.12-0.2.0
+
+### Performance improvements
+
+- Native shuffle is now enabled by default
+- Improved handling of decimal types
+- Reduced some redundant copying of batches in Filter/Scan operations
+- Optimized performance of count aggregates
+- Optimized performance of  CASE expressions for specific uses:
+  - CASE WHEN expr THEN column ELSE null END
+  - CASE WHEN expr THEN literal ELSE literal END
+- Optimized performance of IS NOT NULL
+
+### New Features
+
+- Window operations now support count and sum aggregates
+- CreateArray
+- GetStructField
+- Support nested types in hash join
+- Basic implementation of RLIKE expression
+
+## Current Performance
+
+We use benchmarks derived from the industry standard TPC-H and TPC-DS benchmarks for tracking progress with
+performance. The following charts shows the time it takes to run the queries against 100 GB of data in
+Parquet format using a single executor with eight cores. See the [Comet Benchmarking Guide]
+for details of the environment used for these benchmarks.
+
+[Comet Benchmarking Guide]: https://datafusion.apache.org/comet/contributor-guide/benchmarking.html
+
+### Benchmark derived from TPC-H
+
+Comet 0.2.0 provides a 62% speedup compared to Spark. This is slightly better than the Comet 0.1.0 release.
+
+<img
+src="{{ site.baseurl }}/img/comet-0.2.0/tpch_allqueries.png"
+width="100%"
+class="img-responsive"
+alt="Chart showing TPC-H benchmark results for Comet 0.2.0"
+/>
+
+### Benchmark derived from TPC-DS
+
+Comet 0.2.0 provides a 21% speedup compared to Spark, which is a significant improvement compared to 
+Comet 0.1.0, which did not provide any speedup for this benchmark.
+
+<img
+src="{{ site.baseurl }}/img/comet-0.2.0/tpcds_allqueries.png"
+width="100%"
+class="img-responsive"
+alt="Chart showing TPC-DS benchmark results for Comet 0.2.0"
+/>
+
+## Getting Involved
+
+The Comet project welcomes new contributors. We use the same [Slack and Discord] channels as the main DataFusion
+project.
+
+[Slack and Discord]: https://datafusion.apache.org/contributor-guide/communication.html#slack-and-discord
+
+The easiest way to get involved is to test Comet with your current Spark jobs and file issues for any bugs or
+performance regressions that you find. See the [Getting Started] guide for instructions on downloading and installing
+Comet.
+
+[Getting Started]: https://datafusion.apache.org/comet/user-guide/installation.html
+
+There are also many [good first issues] waiting for contributions.
+
+[good first issues]: https://github.com/apache/datafusion-comet/contribute