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C++ Client Libraries | Google Cloud

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Override Retry, Backoff, and Idempotency Policies

When it is safe to do so, the library automatically retries requests that fail due to a transient error. The library then uses exponential backoff to backoff before trying again. Which operations are considered safe to retry, which errors are treated as transient failures, the details of the exponential backoff algorithm, and for how long the library retries are all configurable via policies.

This document provides examples showing how to override the default policies.

The policies can be set when the *Connection object is created. The library provides default policies for any policy that is not set. The application can also override some (or all) policies when the *Client object is created. This can be useful if multiple *Client objects share the same *Connection object, but you want different retry behavior in some of the clients. Finally, the application can override some retry policies when calling a specific member function.

The library uses three different options to control the retry loop. The options have per-client names.

Configuring the transient errors and retry duration

The *RetryPolicyOption controls:

You can provide your own class for this option. The library also provides two built-in policies:

Note that a library may have more than one version of these classes. Their name match the *Client and *Connection object they are intended to be used with. Some *Client objects treat different error codes as transient errors. In most cases, only kUnavailable is treated as a transient error.

Controlling the backoff algorithm

The *BackoffPolicyOption controls how long the client library will wait before retrying a request that failed with a transient error. You can provide your own class for this option.

The only built-in backoff policy is ExponentialBackoffPolicy. This class implements a truncated exponential backoff algorithm, with jitter. In summary, it doubles the current backoff time after each failure. The actual backoff time for an RPC is chosen at random, but never exceeds the current backoff. The current backoff is doubled after each failure, but never exceeds (or is "truncated") if it reaches a prescribed maximum.

Controlling which operations are retryable

The *IdempotencyPolicyOption controls which requests are retryable, as some requests are never safe to retry.

Only one built-in idempotency policy is provided by the library. The name matches the name of the client it is intended for. For example, FooBarClient will use FooBarIdempotencyPolicy. This policy is very conservative.

Example

For example, this will override the retry policies for monitoring_dashboard_v1::DashboardsServiceClient:

  auto options =
      google::cloud::Options{}
          .set<google::cloud::monitoring_dashboard_v1::
                   DashboardsServiceConnectionIdempotencyPolicyOption>(
              CustomIdempotencyPolicy().clone())
          .set<google::cloud::monitoring_dashboard_v1::
                   DashboardsServiceRetryPolicyOption>(
              google::cloud::monitoring_dashboard_v1::
                  DashboardsServiceLimitedErrorCountRetryPolicy(3)
                      .clone())
          .set<google::cloud::monitoring_dashboard_v1::
                   DashboardsServiceBackoffPolicyOption>(
              google::cloud::ExponentialBackoffPolicy(
                  /*initial_delay=*/std::chrono::milliseconds(200),
                  /*maximum_delay=*/std::chrono::seconds(45),
                  /*scaling=*/2.0)
                  .clone());
  auto connection =
      google::cloud::monitoring_dashboard_v1::MakeDashboardsServiceConnection(
          options);

  // c1 and c2 share the same retry policies
  auto c1 = google::cloud::monitoring_dashboard_v1::DashboardsServiceClient(
      connection);
  auto c2 = google::cloud::monitoring_dashboard_v1::DashboardsServiceClient(
      connection);

  // You can override any of the policies in a new client. This new client
  // will share the policies from c1 (or c2) *except* for the retry policy.
  auto c3 = google::cloud::monitoring_dashboard_v1::DashboardsServiceClient(
      connection, google::cloud::Options{}
                      .set<google::cloud::monitoring_dashboard_v1::
                               DashboardsServiceRetryPolicyOption>(
                          google::cloud::monitoring_dashboard_v1::
                              DashboardsServiceLimitedTimeRetryPolicy(
                                  std::chrono::minutes(5))
                                  .clone()));

  // You can also override the policies in a single call:
  // c3.SomeRpc(..., google::cloud::Options{}
  //     .set<google::cloud::monitoring_dashboard_v1::DashboardsServiceRetryPolicyOption>(
  //       google::cloud::monitoring_dashboard_v1::DashboardsServiceLimitedErrorCountRetryPolicy(10).clone()));

This assumes you have created a custom idempotency policy. Such as:

class CustomIdempotencyPolicy
    : public google::cloud::monitoring_dashboard_v1::
          DashboardsServiceConnectionIdempotencyPolicy {
 public:
  ~CustomIdempotencyPolicy() override = default;
  std::unique_ptr<google::cloud::monitoring_dashboard_v1::
                      DashboardsServiceConnectionIdempotencyPolicy>
  clone() const override {
    return std::make_unique<CustomIdempotencyPolicy>(*this);
  }
  // Override inherited functions to define as needed.
};

Follow these links to find examples for other *Client classes:

More Information See Also

google::cloud::Options

See Also

google::cloud::BackoffPolicy

See Also

google::cloud::ExponentialBackoffPolicy

Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License. For details, see the Google Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates.

Last updated 2025-08-14 UTC.

[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14 UTC."],[[["This document provides guidance on how to override default policies for retrying requests that fail due to transient errors in the library, including the use of exponential backoff and configurable retry policies."],["The library offers three main options for controlling the retry process: `*RetryPolicyOption` for defining transient errors and retry duration, `*BackoffPolicyOption` for managing the backoff algorithm, and `*IdempotencyPolicyOption` for specifying which operations are safe to retry."],["The library includes built-in policies like `*LimitedErrorCountRetryPolicy`, `*LimitedTimeRetryPolicy`, and `ExponentialBackoffPolicy`, and users can define custom policies to suit their needs."],["Policies can be configured when creating a `*Connection` object, when creating a `*Client` object, or even on a per-call basis, allowing flexibility in managing retry behavior across different clients and operations."],["Examples and links are provided for various `*Client` classes, demonstrating how to override retry policies for services like `DashboardsServiceClient`, `MetricsScopesClient`, and others."]]],[]]

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