Configurar o tempo limite da transação

Esta página descreve como definir um tempo limite para transações usando as bibliotecas de cliente do Spanner. A transação falha com um erro DEADLINE_EXCEEDED se não puder ser concluída dentro do valor de tempo limite especificado.

É possível definir valores de tempo limite para transações e para instruções de solicitação de RPC. Definir um valor de tempo limite mais longo para a transação do que o valor de tempo limite da instrução executada na transação não aumenta o tempo limite da instrução, que é limitado pelo próprio valor de tempo limite.

Além disso, se o erro de tempo limite ocorrer durante a execução da solicitação Commit, ainda será possível que a transação tenha sido confirmada.

É possível definir um tempo limite de transação usando as bibliotecas de cliente Go e Java.

Go

import (
	"context"
	"errors"
	"fmt"
	"io"
	"time"

	"cloud.google.com/go/spanner"
	"google.golang.org/api/iterator"
	"google.golang.org/grpc/codes"
)

func transactionTimeout(w io.Writer, db string) error {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, db)
	if err != nil {
		return err
	}
	defer client.Close()

	// Create a context with a 60-second timeout and use this context to run a read/write transaction.
	// This context timeout will be applied to the entire transaction, and the transaction will fail
	// if it cannot finish within the specified timeout value. The Spanner client library applies the
	// (remainder of the) timeout to each statement that is executed in the transaction.
	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
	defer cancel()

	_, err = client.ReadWriteTransaction(ctx, func(ctx context.Context, txn *spanner.ReadWriteTransaction) error {
		selectStmt := spanner.Statement{
			SQL: `SELECT SingerId, FirstName, LastName FROM Singers ORDER BY LastName, FirstName`,
		}
		// The context that is passed in to the transaction function should be used for each statement
		// is executed.
		iter := txn.Query(ctx, selectStmt)
		defer iter.Stop()
		for {
			row, err := iter.Next()
			if errors.Is(err, iterator.Done) {
				break
			}
			if err != nil {
				return err
			}
			var singerID int64
			var firstName, lastName string
			if err := row.Columns(&singerID, &firstName, &lastName); err != nil {
				return err
			}
			fmt.Fprintf(w, "%d %s %s\n", singerID, firstName, lastName)
		}
		stmt := spanner.Statement{
			SQL: `INSERT INTO Singers (SingerId, FirstName, LastName)
					VALUES (38, 'George', 'Washington')`,
		}
		rowCount, err := txn.Update(ctx, stmt)
		if err != nil {
			return err
		}
		fmt.Fprintf(w, "%d record(s) inserted.\n", rowCount)
		return nil
	})
	// Check if an error was returned by the transaction.
	// The spanner.ErrCode(err) function will return codes.OK if err == nil.
	code := spanner.ErrCode(err)
	if code == codes.OK {
		fmt.Fprintf(w, "Transaction with timeout was executed successfully\n")
	} else if code == codes.DeadlineExceeded {
		fmt.Fprintf(w, "Transaction timed out\n")
	} else {
		fmt.Fprintf(w, "Transaction failed with error code %v\n", code)
	}
	return err
}

Java

import com.google.cloud.spanner.DatabaseClient;
import com.google.cloud.spanner.DatabaseId;
import com.google.cloud.spanner.ResultSet;
import com.google.cloud.spanner.Spanner;
import com.google.cloud.spanner.SpannerOptions;
import com.google.cloud.spanner.Statement;
import io.grpc.Context;
import io.grpc.Context.CancellableContext;
import io.grpc.Deadline;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

/**
 * Sample showing how to set a timeout for an entire transaction for the Cloud Spanner Java client.
 */
class TransactionTimeoutExample {

  static void executeTransactionWithTimeout() {
    // TODO(developer): Replace these variables before running the sample.
    String projectId = "my-project";
    String instanceId = "my-instance";
    String databaseId = "my-database";

    executeTransactionWithTimeout(projectId, instanceId, databaseId, 60L, TimeUnit.SECONDS);
  }

  // Execute a read/write transaction with a timeout for the entire transaction.
  static void executeTransactionWithTimeout(
      String projectId,
      String instanceId,
      String databaseId,
      long timeoutValue,
      TimeUnit timeoutUnit) {
    try (Spanner spanner = SpannerOptions.newBuilder().setProjectId(projectId).build()
        .getService()) {
      DatabaseClient client =
          spanner.getDatabaseClient(DatabaseId.of(projectId, instanceId, databaseId));
      // Create a gRPC context with a deadline and with cancellation.
      // gRPC context deadlines require the use of a scheduled executor.
      ScheduledExecutorService executor = Executors.newSingleThreadScheduledExecutor();
      try (CancellableContext context =
          Context.current()
              .withDeadline(Deadline.after(timeoutValue, timeoutUnit), executor)
              .withCancellation()) {
        context.run(
            () -> {
              client
                  .readWriteTransaction()
                  .run(
                      transaction -> {
                        try (ResultSet resultSet =
                            transaction.executeQuery(
                                Statement.of(
                                    "SELECT SingerId, FirstName, LastName\n"
                                        + "FROM Singers\n"
                                        + "ORDER BY LastName, FirstName"))) {
                          while (resultSet.next()) {
                            System.out.printf(
                                "%d %s %s\n",
                                resultSet.getLong("SingerId"),
                                resultSet.getString("FirstName"),
                                resultSet.getString("LastName"));
                          }
                        }
                        String sql =
                            "INSERT INTO Singers (SingerId, FirstName, LastName)\n"
                                + "VALUES (20, 'George', 'Washington')";
                        long rowCount = transaction.executeUpdate(Statement.of(sql));
                        System.out.printf("%d record inserted.%n", rowCount);
                        return null;
                      });
            });
      }
    }
  }
}