Retry, Backoff, and Idempotency Policies.

The library automatically retries requests that fail with transient errors, and follows the recommended practices with respect to backoff between retries.

Application developers can override the default retry and backoff policies.

The default policies are to continue retrying for up to 15 minutes, and to use truncated (at 5 minutes) exponential backoff, doubling the maximum backoff period between retries.

  namespace spanner = ::google::cloud::spanner;
  using ::google::cloud::StatusOr;
  [](std::string const& project_id, std::string const& instance_id,
     std::string const& database_id) {
    // Use a truncated exponential backoff with jitter to wait between
    // retries:
    //   https://en.wikipedia.org/wiki/Exponential_backoff
    //   https://cloud.google.com/storage/docs/exponential-backoff
    auto client = spanner::Client(spanner::MakeConnection(
        spanner::Database(project_id, instance_id, database_id),
        google::cloud::Options{}
            .set<spanner::SpannerRetryPolicyOption>(
                std::make_shared<spanner::LimitedTimeRetryPolicy>(
                    /*maximum_duration=*/std::chrono::seconds(60)))
            .set<spanner::SpannerBackoffPolicyOption>(
                std::make_shared<spanner::ExponentialBackoffPolicy>(
                    /*initial_delay=*/std::chrono::milliseconds(500),
                    /*maximum_delay=*/std::chrono::seconds(64),
                    /*scaling=*/1.5))));
 
    std::int64_t rows_inserted;
    auto commit_result = client.Commit(
        [&client, &rows_inserted](
            spanner::Transaction txn) -> StatusOr<spanner::Mutations> {
          auto insert = client.ExecuteDml(
              std::move(txn),
              spanner::SqlStatement(
                  "INSERT INTO Singers (SingerId, FirstName, LastName)"
                  "  VALUES (20, 'George', 'Washington')"));
          if (!insert) return std::move(insert).status();
          rows_inserted = insert->RowsModified();
          return spanner::Mutations{};
        });
    if (!commit_result) throw std::move(commit_result).status();
    std::cout << "Rows inserted: " << rows_inserted;
  }

See also

`LimitedTimeRetryPolicy` and `LimitedErrorCountRetryPolicy` for alternative retry policies.

`ExponentialBackoffPolicy` to configure different parameters for the exponential backoff policy.