Configura il timeout della transazione

Questa pagina descrive come impostare un timeout per le transazioni utilizzando le librerie client Spanner. La transazione non va a buon fine con un errore DEADLINE_EXCEEDED se non riesce a essere completata entro il valore di timeout specificato.

Puoi impostare valori di timeout per le transazioni e per i comandi di richiesta RPC. L'impostazione di un valore di timeout più lungo per la transazione rispetto al valore di timeout per l'istruzione eseguita nella transazione non aumenta il valore di timeout per l'istruzione, che è vincolato dal proprio valore di timeout.

Inoltre, se l'errore di timeout si verifica durante l'esecuzione della richiesta Commit, è comunque possibile che la transazione sia stata committata.

Puoi impostare un timeout della transazione utilizzando le librerie client Go e Java.

Vai

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;
                      });
            });
      }
    }
  }
}