docs/source/substrait.rst

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=========
Substrait
=========

The ``arrow-dataset`` module can execute Substrait_ plans via the :external+arrow:doc:`Acero <cpp/streaming_execution>`
query engine.

Executing Queries Using Substrait Plans
=======================================

Plans can reference data in files via URIs, or "named tables" that must be provided along with the plan.

Here is an example of a Java program that queries a Parquet file using Java Substrait
(this example use `Substrait Java`_ project to compile a SQL query to a Substrait plan):

.. code-block:: Java

    import com.google.common.collect.ImmutableList;
    import io.substrait.isthmus.SqlToSubstrait;
    import io.substrait.proto.Plan;
    import org.apache.arrow.dataset.file.FileFormat;
    import org.apache.arrow.dataset.file.FileSystemDatasetFactory;
    import org.apache.arrow.dataset.jni.NativeMemoryPool;
    import org.apache.arrow.dataset.scanner.ScanOptions;
    import org.apache.arrow.dataset.scanner.Scanner;
    import org.apache.arrow.dataset.source.Dataset;
    import org.apache.arrow.dataset.source.DatasetFactory;
    import org.apache.arrow.dataset.substrait.AceroSubstraitConsumer;
    import org.apache.arrow.memory.BufferAllocator;
    import org.apache.arrow.memory.RootAllocator;
    import org.apache.arrow.vector.ipc.ArrowReader;
    import org.apache.calcite.sql.parser.SqlParseException;

    import java.nio.ByteBuffer;
    import java.util.HashMap;
    import java.util.Map;

    public class ClientSubstrait {
        public static void main(String[] args) {
            String uri = "file:///data/tpch_parquet/nation.parquet";
            ScanOptions options = new ScanOptions(/*batchSize*/ 32768);
            try (
                BufferAllocator allocator = new RootAllocator();
                DatasetFactory datasetFactory = new FileSystemDatasetFactory(allocator, NativeMemoryPool.getDefault(),
                        FileFormat.PARQUET, uri);
                Dataset dataset = datasetFactory.finish();
                Scanner scanner = dataset.newScan(options);
                ArrowReader reader = scanner.scanBatches()
            ) {
                // map table to reader
                Map<String, ArrowReader> mapTableToArrowReader = new HashMap<>();
                mapTableToArrowReader.put("NATION", reader);
                // get binary plan
                Plan plan = getPlan();
                ByteBuffer substraitPlan = ByteBuffer.allocateDirect(plan.toByteArray().length);
                substraitPlan.put(plan.toByteArray());
                // run query
                try (ArrowReader arrowReader = new AceroSubstraitConsumer(allocator).runQuery(
                        substraitPlan,
                        mapTableToArrowReader
                )) {
                    while (arrowReader.loadNextBatch()) {
                        System.out.println(arrowReader.getVectorSchemaRoot().contentToTSVString());
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        static Plan getPlan() throws SqlParseException {
            String sql = "SELECT * from nation";
            String nation = "CREATE TABLE NATION (N_NATIONKEY BIGINT NOT NULL, N_NAME CHAR(25), " +
                    "N_REGIONKEY BIGINT NOT NULL, N_COMMENT VARCHAR(152))";
            SqlToSubstrait sqlToSubstrait = new SqlToSubstrait();
            Plan plan = sqlToSubstrait.execute(sql, ImmutableList.of(nation));
            return plan;
        }
    }

.. code-block:: text

    // Results example:
    FieldPath(0)    FieldPath(1)    FieldPath(2)    FieldPath(3)
    0               ALGERIA         0               haggle. carefully final deposits detect slyly agai
    1               ARGENTINA       1               al foxes promise slyly according to the regular accounts. bold requests alon

Executing Projections and Filters Using Extended Expressions
============================================================

Dataset also supports projections and filters with Substrait's `Extended Expression`_.
This requires the substrait-java library.

This Java program:

- Loads a Parquet file containing the "nation" table from the TPC-H benchmark.
- Applies a filter:
    - ``N_NATIONKEY > 18``
- Projects two new columns:
    - ``N_REGIONKEY + 10``
    - ``N_NAME || ' - ' || N_COMMENT``



.. code-block:: Java

    import com.google.common.collect.ImmutableList;
    import io.substrait.isthmus.SqlExpressionToSubstrait;
    import io.substrait.proto.ExtendedExpression;
    import org.apache.arrow.dataset.file.FileFormat;
    import org.apache.arrow.dataset.file.FileSystemDatasetFactory;
    import org.apache.arrow.dataset.jni.NativeMemoryPool;
    import org.apache.arrow.dataset.scanner.ScanOptions;
    import org.apache.arrow.dataset.scanner.Scanner;
    import org.apache.arrow.dataset.source.Dataset;
    import org.apache.arrow.dataset.source.DatasetFactory;
    import org.apache.arrow.memory.BufferAllocator;
    import org.apache.arrow.memory.RootAllocator;
    import org.apache.arrow.vector.ipc.ArrowReader;
    import org.apache.calcite.sql.parser.SqlParseException;

    import java.nio.ByteBuffer;
    import java.util.Base64;
    import java.util.Optional;

    public class ClientSubstraitExtendedExpressionsCookbook {

      public static void main(String[] args) throws SqlParseException {
        projectAndFilterDataset();
      }

      private static void projectAndFilterDataset() throws SqlParseException {
        String uri = "file:///Users/data/tpch_parquet/nation.parquet";
        ScanOptions options =
            new ScanOptions.Builder(/*batchSize*/ 32768)
                .columns(Optional.empty())
                .substraitFilter(getByteBuffer(new String[]{"N_NATIONKEY > 18"}))
                .substraitProjection(getByteBuffer(new String[]{"N_REGIONKEY + 10",
                    "N_NAME || CAST(' - ' as VARCHAR) || N_COMMENT"}))
                .build();
        try (BufferAllocator allocator = new RootAllocator();
             DatasetFactory datasetFactory =
                 new FileSystemDatasetFactory(
                     allocator, NativeMemoryPool.getDefault(), FileFormat.PARQUET, uri);
             Dataset dataset = datasetFactory.finish();
             Scanner scanner = dataset.newScan(options);
             ArrowReader reader = scanner.scanBatches()) {
          while (reader.loadNextBatch()) {
            System.out.println(reader.getVectorSchemaRoot().contentToTSVString());
          }
        } catch (Exception e) {
          throw new RuntimeException(e);
        }
      }

      private static ByteBuffer getByteBuffer(String[] sqlExpression) throws SqlParseException {
        String schema =
            "CREATE TABLE NATION (N_NATIONKEY INT NOT NULL, N_NAME VARCHAR, "
                + "N_REGIONKEY INT NOT NULL, N_COMMENT VARCHAR)";
        SqlExpressionToSubstrait expressionToSubstrait = new SqlExpressionToSubstrait();
        ExtendedExpression expression =
            expressionToSubstrait.convert(sqlExpression, ImmutableList.of(schema));
        byte[] expressionToByte =
            Base64.getDecoder().decode(Base64.getEncoder().encodeToString(expression.toByteArray()));
        ByteBuffer byteBuffer = ByteBuffer.allocateDirect(expressionToByte.length);
        byteBuffer.put(expressionToByte);
        return byteBuffer;
      }
    }

.. code-block:: text

    column-1  column-2
    13        ROMANIA - ular asymptotes are about the furious multipliers. express dependencies nag above the ironically ironic account
    14        SAUDI ARABIA - ts. silent requests haggle. closely express packages sleep across the blithely
    12        VIETNAM - hely enticingly express accounts. even, final
    13        RUSSIA -  requests against the platelets use never according to the quickly regular pint
    13        UNITED KINGDOM - eans boost carefully special requests. accounts are. carefull
    11        UNITED STATES - y final packages. slow foxes cajole quickly. quickly silent platelets breach ironic accounts. unusual pinto be

.. _`Substrait`: https://substrait.io/
.. _`Substrait Java`: https://github.com/substrait-io/substrait-java
.. _`Acero`: https://arrow.apache.org/docs/cpp/streaming_execution.html
.. _`Extended Expression`: https://github.com/substrait-io/substrait/blob/main/site/docs/expressions/extended_expression.md