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| <section id="development"> |
| <h1>Development<a class="headerlink" href="#development" title="Link to this heading">#</a></h1> |
| <section id="build-prerequisites"> |
| <h2>Build prerequisites<a class="headerlink" href="#build-prerequisites" title="Link to this heading">#</a></h2> |
| <ul class="simple"> |
| <li><p>JDK 17 or newer.</p></li> |
| <li><p>Rust toolchain (stable, installed via <a class="reference external" href="https://rustup.rs/">rustup</a>).</p></li> |
| <li><p><a class="reference external" href="https://github.com/clflushopt/tpchgen-rs"><code class="docutils literal notranslate"><span class="pre">tpchgen-cli</span></code></a> — only needed to generate test data for the Parquet |
| integration test (<code class="docutils literal notranslate"><span class="pre">cargo</span> <span class="pre">install</span> <span class="pre">tpchgen-cli</span></code>).</p></li> |
| </ul> |
| <p>Maven is bundled via the <code class="docutils literal notranslate"><span class="pre">./mvnw</span></code> wrapper; no separate Maven install is |
| required.</p> |
| </section> |
| <section id="build-and-test"> |
| <h2>Build and test<a class="headerlink" href="#build-and-test" title="Link to this heading">#</a></h2> |
| <div class="highlight-sh notranslate"><div class="highlight"><pre><span></span>make<span class="w"> </span><span class="nb">test</span> |
| </pre></div> |
| </div> |
| <p>This builds the native Rust crate and runs the JUnit tests. The steps can |
| be run individually:</p> |
| <div class="highlight-sh notranslate"><div class="highlight"><pre><span></span>cargo<span class="w"> </span>build<span class="w"> </span>--workspace |
| ./mvnw<span class="w"> </span><span class="nb">test</span> |
| </pre></div> |
| </div> |
| <p>The native library must be built before running JVM tests.</p> |
| <p>Before pushing, run <code class="docutils literal notranslate"><span class="pre">make</span> <span class="pre">format</span></code> to apply the Java + Rust formatters in |
| place. CI verifies formatting, clippy, and license headers on every PR.</p> |
| <p>The first build in a fresh checkout reaches out to |
| <code class="docutils literal notranslate"><span class="pre">raw.githubusercontent.com</span></code> to fetch the DataFusion <code class="docutils literal notranslate"><span class="pre">.proto</span></code> files used |
| to generate the <code class="docutils literal notranslate"><span class="pre">datafusion-proto</span></code> Java classes. Subsequent builds are |
| offline; the <code class="docutils literal notranslate"><span class="pre">download-maven-plugin</span></code> cache under |
| <code class="docutils literal notranslate"><span class="pre">~/.m2/repository/.cache/</span></code> satisfies them.</p> |
| </section> |
| <section id="test-data"> |
| <h2>Test data<a class="headerlink" href="#test-data" title="Link to this heading">#</a></h2> |
| <p>The Parquet integration test reads TPC-H SF1 data (~345 MB across 8 tables |
| in Snappy-compressed Parquet). Generate it once with:</p> |
| <div class="highlight-sh notranslate"><div class="highlight"><pre><span></span>make<span class="w"> </span>tpch-data |
| </pre></div> |
| </div> |
| <p>Tests that need this data skip cleanly if it is missing. <code class="docutils literal notranslate"><span class="pre">make</span> <span class="pre">clean</span></code> |
| does <strong>not</strong> remove <code class="docutils literal notranslate"><span class="pre">tpch-data/</span></code> — delete it manually to reclaim the |
| disk space.</p> |
| </section> |
| <section id="repository-layout"> |
| <h2>Repository layout<a class="headerlink" href="#repository-layout" title="Link to this heading">#</a></h2> |
| <p>The repository is a multi-module Maven build:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">Cargo.toml</span></code> — Rust workspace root declaring the crate members |
| (<code class="docutils literal notranslate"><span class="pre">native</span></code>, <code class="docutils literal notranslate"><span class="pre">native-common</span></code>) and <code class="docutils literal notranslate"><span class="pre">[workspace.dependencies]</span></code> that pin |
| shared versions in one place. Cargo writes artifacts to <code class="docutils literal notranslate"><span class="pre">rust-target/</span></code> |
| (overridden in <code class="docutils literal notranslate"><span class="pre">.cargo/config.toml</span></code>) so <code class="docutils literal notranslate"><span class="pre">mvn</span> <span class="pre">clean</span></code> at the repo root does |
| not nuke the Rust build cache.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">pom.xml</span></code> — parent POM declaring the <code class="docutils literal notranslate"><span class="pre">core</span></code> and <code class="docutils literal notranslate"><span class="pre">examples</span></code> modules and |
| shared plugin/dependency versions.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">core/</span></code> — <code class="docutils literal notranslate"><span class="pre">datafusion-java</span></code> library module (Java sources, tests, and |
| generated protobuf classes).</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">examples/</span></code> — <code class="docutils literal notranslate"><span class="pre">datafusion-java-examples</span></code> module containing runnable |
| examples that depend on the library; built alongside the library so they |
| cannot fall out of sync with the API.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">native/</span></code> — <code class="docutils literal notranslate"><span class="pre">datafusion-jni</span></code> Rust crate (JNI + Arrow C Data Interface).</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">native-common/</span></code> — <code class="docutils literal notranslate"><span class="pre">datafusion-jni-common</span></code> Rust crate: JNI plumbing |
| shared across native crates (error→exception mapping, the per-cdylib |
| Tokio runtime singleton, the async-stream→<code class="docutils literal notranslate"><span class="pre">FFI_ArrowArrayStream</span></code> bridge).</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">proto/</span></code> — Protobuf definitions shared between Java and Rust.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">Makefile</span></code> — top-level build orchestration (<code class="docutils literal notranslate"><span class="pre">make</span> <span class="pre">test</span></code>, <code class="docutils literal notranslate"><span class="pre">make</span> <span class="pre">format</span></code>, |
| <code class="docutils literal notranslate"><span class="pre">make</span> <span class="pre">tpch-data</span></code>).</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">mvnw</span></code>, <code class="docutils literal notranslate"><span class="pre">mvnw.cmd</span></code> — bundled Maven wrapper.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">docs/</span></code> — Sphinx documentation source and build scripts.</p></li> |
| </ul> |
| </section> |
| <section id="running-an-example"> |
| <h2>Running an example<a class="headerlink" href="#running-an-example" title="Link to this heading">#</a></h2> |
| <p>The examples module wires <code class="docutils literal notranslate"><span class="pre">exec-maven-plugin</span></code> with the right |
| <code class="docutils literal notranslate"><span class="pre">java.library.path</span></code> and <code class="docutils literal notranslate"><span class="pre">--add-opens</span></code> flags. Install the library to the |
| local Maven repository once, then run any example by main class:</p> |
| <div class="highlight-sh notranslate"><div class="highlight"><pre><span></span>./mvnw<span class="w"> </span>install<span class="w"> </span>-DskipTests |
| ./mvnw<span class="w"> </span>-pl<span class="w"> </span>:datafusion-java-examples<span class="w"> </span>exec:exec<span class="w"> </span><span class="se">\</span> |
| <span class="w"> </span>-Dexec.mainClass<span class="o">=</span>org.apache.datafusion.examples.SqlQueryExample |
| </pre></div> |
| </div> |
| <p>The bundled examples (under |
| <code class="docutils literal notranslate"><span class="pre">examples/src/main/java/org/apache/datafusion/examples/</span></code>):</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">SqlQueryExample</span></code> — register a CSV and run a SQL aggregation.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">DataFrameExample</span></code> — read CSV → filter / select / rename / distinct → |
| write Parquet → read back.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">ProtoPlanExample</span></code> — build a DataFusion <code class="docutils literal notranslate"><span class="pre">LogicalPlanNode</span></code> directly via |
| the generated protobuf classes and execute it through |
| <code class="docutils literal notranslate"><span class="pre">SessionContext.fromProto</span></code>.</p></li> |
| </ul> |
| <p>Re-run <code class="docutils literal notranslate"><span class="pre">mvnw</span> <span class="pre">install</span> <span class="pre">-DskipTests</span></code> whenever you change the library.</p> |
| </section> |
| <section id="passing-structured-options-across-the-jni-boundary"> |
| <h2>Passing structured options across the JNI boundary<a class="headerlink" href="#passing-structured-options-across-the-jni-boundary" title="Link to this heading">#</a></h2> |
| <p>When a JNI call needs to carry more than a handful of scalar arguments — |
| for example, a struct of nullable knobs like <code class="docutils literal notranslate"><span class="pre">CsvReadOptions</span></code> or |
| <code class="docutils literal notranslate"><span class="pre">SessionOptions</span></code> — encode the call’s configuration as a protobuf message |
| rather than expanding the JNI signature with one parameter per field.</p> |
| <p>Add a <code class="docutils literal notranslate"><span class="pre">.proto</span></code> file under <code class="docutils literal notranslate"><span class="pre">proto/</span></code>, declare <code class="docutils literal notranslate"><span class="pre">package</span> <span class="pre">datafusion_java;</span></code>, |
| and follow the conventions already in use:</p> |
| <ul class="simple"> |
| <li><p>One message per logical bundle of options.</p></li> |
| <li><p>Use <code class="docutils literal notranslate"><span class="pre">optional</span></code> for fields whose unset-ness must survive the boundary |
| (so the Rust side can leave a DataFusion default in place).</p></li> |
| <li><p>Use proto enums for closed sets of choices instead of strings. |
| Prefix every value with the enum’s name (e.g. |
| <code class="docutils literal notranslate"><span class="pre">FILE_COMPRESSION_TYPE_GZIP</span></code>, not bare <code class="docutils literal notranslate"><span class="pre">GZIP</span></code>) because proto3 enum |
| values are scoped at the package level, and the zero value must be a |
| <code class="docutils literal notranslate"><span class="pre">_UNSPECIFIED</span></code> sentinel — the Rust side should reject <code class="docutils literal notranslate"><span class="pre">UNSPECIFIED</span></code> |
| rather than silently default it.</p></li> |
| <li><p>Keep large opaque payloads (Arrow IPC schemas, plan nodes) as separate |
| <code class="docutils literal notranslate"><span class="pre">byte[]</span></code> JNI arguments next to the options proto, not inside it.</p></li> |
| <li><p>Suffix the message name with <code class="docutils literal notranslate"><span class="pre">Proto</span></code> if a sibling Java class would |
| otherwise shadow it (e.g. <code class="docutils literal notranslate"><span class="pre">CsvReadOptionsProto</span></code> vs the public |
| <code class="docutils literal notranslate"><span class="pre">CsvReadOptions</span></code>).</p></li> |
| </ul> |
| <p>The proto is compiled by both <code class="docutils literal notranslate"><span class="pre">prost-build</span></code> (Rust, via <code class="docutils literal notranslate"><span class="pre">native/build.rs</span></code>) |
| and the Maven <code class="docutils literal notranslate"><span class="pre">protobuf-maven-plugin</span></code> (Java). The Java side builds the |
| message, serializes to bytes, and passes the byte array through JNI; the |
| Rust side decodes once and folds the fields into the corresponding |
| DataFusion struct.</p> |
| <p>This pattern keeps JNI signatures short, makes nullable and enum fields |
| explicit in a single typed schema, and lets new fields be added without |
| touching the signature on either side.</p> |
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