docs/source/java/substrait.rst

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

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

Executing 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

.. _`Substrait`: https://substrait.io/
.. _`Substrait Java`: https://github.com/substrait-io/substrait-java
.. _`Acero`: https://arrow.apache.org/docs/cpp/streaming_execution.html