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| <section id="read"> |
| <h1>Read<a class="headerlink" href="#read" title="Link to this heading">#</a></h1> |
| <p>Paimon by functionality can be divided into two layers:</p> |
| <ul class="simple"> |
| <li><p>Control Plane: Responsible for accessing and managing Meta (snapshot, manifest, etc.), including: |
| - Catalog / Database access |
| - Table retrieval |
| - Collection and resolution of data files</p></li> |
| <li><p>Data Plane: Responsible for accessing actual data files, including: |
| - Readers for various file formats |
| - Coordinated reading of file collections</p></li> |
| </ul> |
| <p>The control plane and data plane interact primarily via DataSplit (the query plan). C++ Paimon currently supports a standard |
| DataSplit protocol which includes the necessary meta information to access data files. With DataSplit, a high-performance |
| data access path can be integrated.</p> |
| <p>At compute time, the execution engine (reader) does not need to be aware of the concrete table type or its metadata details. |
| It only needs to follow the instructions within the DataSplit (query plan) to perform data reading operations.</p> |
| <p>With the layered abstraction of the control plane and data plane, and the use of DataSplit as a stable protocol interface, |
| the two layers can evolve their functionality and optimize code relatively independently. This design also enables |
| cross-language task scheduling and interaction (e.g., Java and C++), substantially reducing engineering maintenance costs |
| across the two language ecosystems.</p> |
| <section id="schema-evolution"> |
| <h2>Schema Evolution<a class="headerlink" href="#schema-evolution" title="Link to this heading">#</a></h2> |
| <section id="scope-and-compatibility"> |
| <h3>Scope and Compatibility<a class="headerlink" href="#scope-and-compatibility" title="Link to this heading">#</a></h3> |
| <p>C++ Paimon supports all evolution kinds available in Java Paimon for non-nested types:</p> |
| <ul class="simple"> |
| <li><p>Add column</p></li> |
| <li><p>Drop column</p></li> |
| <li><p>Reorder columns</p></li> |
| <li><p>Rename column</p></li> |
| <li><p>Change column type</p></li> |
| </ul> |
| <div class="admonition note"> |
| <p class="admonition-title">Note</p> |
| <ul class="simple"> |
| <li><p>Only non-nested type evolution is supported. Nested columns (struct, array, map) are not supported.</p></li> |
| <li><p>Partition keys: Only column reordering is supported; other operations are not supported (consistent with Java Paimon).</p></li> |
| <li><p>Primary key:</p> |
| <ul> |
| <li><p>Adding or dropping columns is not supported.</p></li> |
| <li><p>Other operations are supported (consistent with Java Paimon).</p></li> |
| </ul> |
| </li> |
| </ul> |
| </div> |
| </section> |
| <section id="per-file-schema-via-field-ids"> |
| <h3>Per-File Schema via Field IDs<a class="headerlink" href="#per-file-schema-via-field-ids" title="Link to this heading">#</a></h3> |
| <p>In DataSplit, each file may have a completely different data schema. Paimon uses field IDs to uniquely identify fields.</p> |
| </section> |
| <section id="overflow-behavior-disclaimer"> |
| <h3>Overflow Behavior Disclaimer<a class="headerlink" href="#overflow-behavior-disclaimer" title="Link to this heading">#</a></h3> |
| <p>Overflow behavior is undefined for C++ and Java Paimon. Results in overflow scenarios may:</p> |
| <ul class="simple"> |
| <li><p>Be incorrect values,</p></li> |
| <li><p>Return an error status,</p></li> |
| <li><p>Or be null.</p></li> |
| </ul> |
| <p>C++ Paimon does not guarantee identical results to Java Paimon in overflow scenarios. Users should not rely on identical |
| return values between implementations.</p> |
| </section> |
| <section id="type-change-support-matrix"> |
| <h3>Type Change Support Matrix<a class="headerlink" href="#type-change-support-matrix" title="Link to this heading">#</a></h3> |
| <p>The table below indicates support for changing a column type from <code class="docutils literal notranslate"><span class="pre">source</span></code> to <code class="docutils literal notranslate"><span class="pre">target</span></code>. Refer to the numbered notes below the table |
| for caveats.</p> |
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| <col style="width: 7.2%" /> |
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| <col style="width: 7.2%" /> |
| <col style="width: 7.2%" /> |
| <col style="width: 7.2%" /> |
| <col style="width: 7.2%" /> |
| <col style="width: 5.8%" /> |
| <col style="width: 8.7%" /> |
| <col style="width: 7.2%" /> |
| <col style="width: 5.8%" /> |
| <col style="width: 13.0%" /> |
| <col style="width: 7.2%" /> |
| </colgroup> |
| <thead> |
| <tr class="row-odd"><th class="head"><p>src \ target</p></th> |
| <th class="head"><p>tinyint</p></th> |
| <th class="head"><p>smallint</p></th> |
| <th class="head"><p>int</p></th> |
| <th class="head"><p>bigint</p></th> |
| <th class="head"><p>float</p></th> |
| <th class="head"><p>double</p></th> |
| <th class="head"><p>bool</p></th> |
| <th class="head"><p>string</p></th> |
| <th class="head"><p>binary</p></th> |
| <th class="head"><p>date</p></th> |
| <th class="head"><p>timestamp (without tz)</p></th> |
| <th class="head"><p>decimal</p></th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr class="row-even"><td><p>tinyint</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>✅</p></td> |
| </tr> |
| <tr class="row-odd"><td><p>smallint</p></td> |
| <td><p>✅ 1️⃣</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>✅</p></td> |
| </tr> |
| <tr class="row-even"><td><p>int</p></td> |
| <td><p>✅ 1️⃣</p></td> |
| <td><p>✅ 1️⃣</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>✅ 1️⃣</p></td> |
| <td><p>✅</p></td> |
| </tr> |
| <tr class="row-odd"><td><p>bigint</p></td> |
| <td><p>✅ 1️⃣</p></td> |
| <td><p>✅ 1️⃣</p></td> |
| <td><p>✅ 1️⃣</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>✅ 6️⃣</p></td> |
| <td><p>✅</p></td> |
| </tr> |
| <tr class="row-even"><td><p>float</p></td> |
| <td><p>✅ 2️⃣</p></td> |
| <td><p>✅ 2️⃣</p></td> |
| <td><p>✅ 2️⃣</p></td> |
| <td><p>✅ 2️⃣</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅ 3️⃣ 4️⃣</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>✅</p></td> |
| </tr> |
| <tr class="row-odd"><td><p>double</p></td> |
| <td><p>✅ 2️⃣</p></td> |
| <td><p>✅ 2️⃣</p></td> |
| <td><p>✅ 2️⃣</p></td> |
| <td><p>✅ 2️⃣</p></td> |
| <td><p>✅ 2️⃣</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅ 3️⃣ 4️⃣</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>✅</p></td> |
| </tr> |
| <tr class="row-even"><td><p>bool</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>✅</p></td> |
| </tr> |
| <tr class="row-odd"><td><p>string</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅ 3️⃣</p></td> |
| <td><p>✅ 3️⃣</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅ 5️⃣</p></td> |
| <td><p>✅ 7️⃣</p></td> |
| </tr> |
| <tr class="row-even"><td><p>binary</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| </tr> |
| <tr class="row-odd"><td><p>date</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>✅</p></td> |
| <td><p>❌</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅ 5️⃣</p></td> |
| <td><p>❌</p></td> |
| </tr> |
| <tr class="row-even"><td><p>timestamp (without tz)</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>✅ 1️⃣</p></td> |
| <td><p>✅</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>✅</p></td> |
| <td><p>❌</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>❌</p></td> |
| </tr> |
| <tr class="row-odd"><td><p>decimal</p></td> |
| <td><p>✅ 1️⃣</p></td> |
| <td><p>✅ 1️⃣</p></td> |
| <td><p>✅ 1️⃣</p></td> |
| <td><p>✅ 1️⃣</p></td> |
| <td><p>✅</p></td> |
| <td><p>✅</p></td> |
| <td><p>❌</p></td> |
| <td><p>✅</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>❌</p></td> |
| <td><p>✅</p></td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| <div class="note admonition"> |
| <p class="admonition-title">Overflow Behavior Notes</p> |
| <dl class="simple"> |
| <dt>1️⃣ Integer downcast overflow behavior matches Java in specific cases.</dt><dd><p>Example: smallint -> tinyint, 32767 becomes -1; int -> smallint, -2147483648 becomes 0.</p> |
| </dd> |
| <dt>2️⃣ Floating-point overflow behavior is partially consistent with Java and partially different.</dt><dd><dl class="simple"> |
| <dt>Example: float -> tinyint</dt><dd><ul class="simple"> |
| <li><p>Java: MAX_FLOAT -> -1, INFINITY -> -1</p></li> |
| <li><p>C++: MAX_FLOAT -> 0, INFINITY -> 0</p></li> |
| </ul> |
| </dd> |
| </dl> |
| </dd> |
| <dt>3️⃣ Keyword differences for special float/double values:</dt><dd><ul class="simple"> |
| <li><p>Java: Infinity, -Infinity, NaN</p></li> |
| <li><p>C++: inf, -inf, nan</p></li> |
| </ul> |
| </dd> |
| <dt>4️⃣ Printing difference:</dt><dd><ul class="simple"> |
| <li><p>C++ Paimon prints 1.0 as <code class="docutils literal notranslate"><span class="pre">1</span></code></p></li> |
| <li><p>Java Paimon prints 1.0 as <code class="docutils literal notranslate"><span class="pre">1.0</span></code></p></li> |
| </ul> |
| </dd> |
| <dt>5️⃣ Timestamp precision and range differences:</dt><dd><ul class="simple"> |
| <li><p>Java Paimon: 0000-01-01 00:00:00.000000000 to 9999-12-31 23:59:59.999999999</p></li> |
| <li><p>C++ Paimon: 1677-09-21 00:12:43.145224192 to 2262-04-11 23:47:16.854775807</p></li> |
| <li><p>C++ only supports nanosecond precision; range is smaller.</p></li> |
| </ul> |
| </dd> |
| <dt>6️⃣ bigint -> timestamp range differences:</dt><dd><ul class="simple"> |
| <li><p>Java Paimon (ms): <code class="docutils literal notranslate"><span class="pre">[MIN_INT64/1000,</span> <span class="pre">MAX_INT64/1000]</span></code> seconds</p></li> |
| <li><p>C++ Paimon (ns): <code class="docutils literal notranslate"><span class="pre">[MIN_INT64/1e9,</span>  <span class="pre">MAX_INT64/1e9]</span></code> seconds</p></li> |
| </ul> |
| </dd> |
| <dt>7️⃣ string -> decimal with precision > 38:</dt><dd><ul class="simple"> |
| <li><p>C++ returns <code class="docutils literal notranslate"><span class="pre">null</span></code> if parsing would overflow 128-bit arithmetic.</p></li> |
| <li><p>Java may rescale and return a value based on the rescaled precision.</p></li> |
| <li><p>Example input: <code class="docutils literal notranslate"><span class="pre">1111111111111111111111111111111111111.15</span></code>, Java returns: <code class="docutils literal notranslate"><span class="pre">1111111111111111111111111111111111111.2</span></code>, C++ returns: <code class="docutils literal notranslate"><span class="pre">null</span></code></p></li> |
| </ul> |
| </dd> |
| </dl> |
| </div> |
| </section> |
| <section id="implementation-guidance"> |
| <h3>Implementation Guidance<a class="headerlink" href="#implementation-guidance" title="Link to this heading">#</a></h3> |
| <ul class="simple"> |
| <li><p>Use DataSplit as the sole interface between control and data planes. Treat it as the canonical query plan contract.</p></li> |
| <li><p>Resolve field types and IDs per file; prefer inline data file metadata, fallback to table schema files when necessary.</p></li> |
| <li><p>Expect per-file schema variability; design readers to align by field IDs rather than positional indices.</p></li> |
| <li><p>Do not assume identical overflow semantics across C++ and Java; tests should validate acceptable ranges and nullability.</p></li> |
| <li><p>For timestamp handling, consider precision/range constraints in C++ when interoperating with Java-produced data splits.</p></li> |
| </ul> |
| </section> |
| </section> |
| </section> |
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