Download table data in the Arrow data format

Download table data using the Arrow data format and deserialize the data into row objects.

Documentation pages that include this code sample

To view the code sample used in context, see the following documentation:

Code sample

Java

Before trying this sample, follow the Java setup instructions in the BigQuery Quickstart Using Client Libraries. For more information, see the BigQuery Java API reference documentation.


import com.google.api.gax.rpc.ServerStream;
import com.google.cloud.bigquery.storage.v1.ArrowRecordBatch;
import com.google.cloud.bigquery.storage.v1.ArrowSchema;
import com.google.cloud.bigquery.storage.v1.BigQueryReadClient;
import com.google.cloud.bigquery.storage.v1.CreateReadSessionRequest;
import com.google.cloud.bigquery.storage.v1.DataFormat;
import com.google.cloud.bigquery.storage.v1.ReadRowsRequest;
import com.google.cloud.bigquery.storage.v1.ReadRowsResponse;
import com.google.cloud.bigquery.storage.v1.ReadSession;
import com.google.cloud.bigquery.storage.v1.ReadSession.TableModifiers;
import com.google.cloud.bigquery.storage.v1.ReadSession.TableReadOptions;
import com.google.common.base.Preconditions;
import com.google.protobuf.Timestamp;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.apache.arrow.memory.BufferAllocator;
import org.apache.arrow.memory.RootAllocator;
import org.apache.arrow.vector.FieldVector;
import org.apache.arrow.vector.VectorLoader;
import org.apache.arrow.vector.VectorSchemaRoot;
import org.apache.arrow.vector.ipc.ReadChannel;
import org.apache.arrow.vector.ipc.message.MessageSerializer;
import org.apache.arrow.vector.types.pojo.Field;
import org.apache.arrow.vector.types.pojo.Schema;
import org.apache.arrow.vector.util.ByteArrayReadableSeekableByteChannel;

public class StorageArrowSample {

  /*
   * SimpleRowReader handles deserialization of the Apache Arrow-encoded row batches transmitted
   * from the storage API using a generic datum decoder.
   */
  private static class SimpleRowReader implements AutoCloseable {

    BufferAllocator allocator = new RootAllocator(Long.MAX_VALUE);

    // Decoder object will be reused to avoid re-allocation and too much garbage collection.
    private final VectorSchemaRoot root;
    private final VectorLoader loader;

    public SimpleRowReader(ArrowSchema arrowSchema) throws IOException {
      Schema schema =
          MessageSerializer.deserializeSchema(
              new ReadChannel(
                  new ByteArrayReadableSeekableByteChannel(
                      arrowSchema.getSerializedSchema().toByteArray())));
      Preconditions.checkNotNull(schema);
      List<FieldVector> vectors = new ArrayList<>();
      for (Field field : schema.getFields()) {
        vectors.add(field.createVector(allocator));
      }
      root = new VectorSchemaRoot(vectors);
      loader = new VectorLoader(root);
    }

    /**
     * Sample method for processing Arrow data which only validates decoding.
     *
     * @param batch object returned from the ReadRowsResponse.
     */
    public void processRows(ArrowRecordBatch batch) throws IOException {
      org.apache.arrow.vector.ipc.message.ArrowRecordBatch deserializedBatch =
          MessageSerializer.deserializeRecordBatch(
              new ReadChannel(
                  new ByteArrayReadableSeekableByteChannel(
                      batch.getSerializedRecordBatch().toByteArray())),
              allocator);

      loader.load(deserializedBatch);
      // Release buffers from batch (they are still held in the vectors in root).
      deserializedBatch.close();
      System.out.println(root.contentToTSVString());
      // Release buffers from vectors in root.
      root.clear();
    }

    @Override
    public void close() {
      root.close();
      allocator.close();
    }
  }

  public static void main(String... args) throws Exception {
    // Sets your Google Cloud Platform project ID.
    // String projectId = "YOUR_PROJECT_ID";
    String projectId = args[0];
    Integer snapshotMillis = null;
    if (args.length > 1) {
      snapshotMillis = Integer.parseInt(args[1]);
    }

    try (BigQueryReadClient client = BigQueryReadClient.create()) {
      String parent = String.format("projects/%s", projectId);

      // This example uses baby name data from the public datasets.
      String srcTable =
          String.format(
              "projects/%s/datasets/%s/tables/%s",
              "bigquery-public-data", "usa_names", "usa_1910_current");

      // We specify the columns to be projected by adding them to the selected fields,
      // and set a simple filter to restrict which rows are transmitted.
      TableReadOptions options =
          TableReadOptions.newBuilder()
              .addSelectedFields("name")
              .addSelectedFields("number")
              .addSelectedFields("state")
              .setRowRestriction("state = \"WA\"")
              .build();

      // Start specifying the read session we want created.
      ReadSession.Builder sessionBuilder =
          ReadSession.newBuilder()
              .setTable(srcTable)
              // This API can also deliver data serialized in Apache Avro format.
              // This example leverages Apache Arrow.
              .setDataFormat(DataFormat.ARROW)
              .setReadOptions(options);

      // Optionally specify the snapshot time.  When unspecified, snapshot time is "now".
      if (snapshotMillis != null) {
        Timestamp t =
            Timestamp.newBuilder()
                .setSeconds(snapshotMillis / 1000)
                .setNanos((int) ((snapshotMillis % 1000) * 1000000))
                .build();
        TableModifiers modifiers = TableModifiers.newBuilder().setSnapshotTime(t).build();
        sessionBuilder.setTableModifiers(modifiers);
      }

      // Begin building the session creation request.
      CreateReadSessionRequest.Builder builder =
          CreateReadSessionRequest.newBuilder()
              .setParent(parent)
              .setReadSession(sessionBuilder)
              .setMaxStreamCount(1);

      ReadSession session = client.createReadSession(builder.build());
      // Setup a simple reader and start a read session.
      try (SimpleRowReader reader = new SimpleRowReader(session.getArrowSchema())) {

        // Assert that there are streams available in the session.  An empty table may not have
        // data available.  If no sessions are available for an anonymous (cached) table, consider
        // writing results of a query to a named table rather than consuming cached results
        // directly.
        Preconditions.checkState(session.getStreamsCount() > 0);

        // Use the first stream to perform reading.
        String streamName = session.getStreams(0).getName();

        ReadRowsRequest readRowsRequest =
            ReadRowsRequest.newBuilder().setReadStream(streamName).build();

        // Process each block of rows as they arrive and decode using our simple row reader.
        ServerStream<ReadRowsResponse> stream = client.readRowsCallable().call(readRowsRequest);
        for (ReadRowsResponse response : stream) {
          Preconditions.checkState(response.hasArrowRecordBatch());
          reader.processRows(response.getArrowRecordBatch());
        }
      }
    }
  }
}