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/*
* Copyright 2010-2015 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License").
* You may not use this file except in compliance with the License.
* A copy of the License is located at
*
* http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. This file is distributed
* on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
* express or implied. See the License for the specific language governing
* permissions and limitations under the License.
*/
package com.amazonaws.retry;
import java.io.IOException;
import java.util.Random;
import org.apache.http.HttpStatus;
import com.amazonaws.AmazonClientException;
import com.amazonaws.AmazonServiceException;
import com.amazonaws.AmazonWebServiceRequest;
import com.amazonaws.ClientConfiguration;
import com.amazonaws.retry.RetryUtils;
/**
* This class includes a set of pre-defined retry policies, including default
* policies used by SDK.
*/
public class PredefinedRetryPolicies {
/* SDK default */
/** SDK default max retry count **/
public static final int DEFAULT_MAX_ERROR_RETRY = 3;
/** SDK default retry policy **/
public static final RetryPolicy DEFAULT;
/* Default for DynamoDB client */
/** Default max retry count for DynamoDB client **/
public static final int DYNAMODB_DEFAULT_MAX_ERROR_RETRY = 10;
/** Default policy for DynamoDB client **/
public static final RetryPolicy DYNAMODB_DEFAULT;
/* Reusable retry policy components */
/**
* The SDK default retry condition, which checks for various conditions in
* the following order:
*
* - Never retry on requests with non-repeatable content;
*
- Retry on client exceptions caused by IOException;
*
- Retry on service exceptions that are either 500 internal server
* errors, 503 service unavailable errors, service throttling errors or
* clock skew errors.
*
*/
public static final RetryPolicy.RetryCondition DEFAULT_RETRY_CONDITION = new SDKDefaultRetryCondition();
/**
* The SDK default back-off strategy, which increases exponentially up to a
* max amount of delay. It also applies a larger scale factor upon service
* throttling exception.
*/
public static final RetryPolicy.BackoffStrategy DEFAULT_BACKOFF_STRATEGY = new SDKDefaultBackoffStrategy();
/**
* The default back-off strategy for DynamoDB client, which increases
* exponentially up to a max amount of delay. Compared to the SDK default
* back-off strategy, it applies a smaller scale factor.
*/
public static final RetryPolicy.BackoffStrategy DYNAMODB_DEFAULT_BACKOFF_STRATEGY = new DynamoDBDefaultBackoffStrategy();
static {
DEFAULT = getDefaultRetryPolicy();
DYNAMODB_DEFAULT = getDynamoDBDefaultRetryPolicy();
}
/**
* Returns the SDK default retry policy. This policy will honor the
* maxErrorRetry set in ClientConfiguration.
*
* @see ClientConfiguration#setMaxErrorRetry(int)
*/
public static RetryPolicy getDefaultRetryPolicy() {
return new RetryPolicy(DEFAULT_RETRY_CONDITION,
DEFAULT_BACKOFF_STRATEGY,
DEFAULT_MAX_ERROR_RETRY,
true);
}
/**
* Returns the default retry policy for DynamoDB client. This policy will
* honor the maxErrorRetry set in ClientConfiguration.
*
* @see ClientConfiguration#setMaxErrorRetry(int)
*/
public static RetryPolicy getDynamoDBDefaultRetryPolicy() {
return new RetryPolicy(DEFAULT_RETRY_CONDITION,
DYNAMODB_DEFAULT_BACKOFF_STRATEGY,
DYNAMODB_DEFAULT_MAX_ERROR_RETRY,
true);
}
/**
* Returns the SDK default retry policy with the specified max retry count.
*/
public static RetryPolicy getDefaultRetryPolicyWithCustomMaxRetries(int maxErrorRetry) {
return new RetryPolicy(DEFAULT_RETRY_CONDITION,
DEFAULT_BACKOFF_STRATEGY,
maxErrorRetry,
false);
}
/**
* Returns the default retry policy for DynamoDB client with the specified
* max retry count.
*/
public static RetryPolicy getDynamoDBDefaultRetryPolicyWithCustomMaxRetries(int maxErrorRetry) {
return new RetryPolicy(DEFAULT_RETRY_CONDITION,
DYNAMODB_DEFAULT_BACKOFF_STRATEGY,
maxErrorRetry,
false);
}
/**
* The default implementation of RetryCondition used by the SDK. User could
* extend this class to provide additional custom conditions.
* The default implementation checks for various conditions in
* the following order:
*
* - Retry on client exceptions caused by IOException;
*
- Retry on service exceptions that are either 500 internal server
* errors, 503 service unavailable errors, service throttling errors or
* clock skew errors.
*
*/
public static class SDKDefaultRetryCondition implements RetryPolicy.RetryCondition {
@Override
public boolean shouldRetry(AmazonWebServiceRequest originalRequest,
AmazonClientException exception,
int retriesAttempted) {
// Always retry on client exceptions caused by IOException
if (exception.getCause() instanceof IOException) return true;
// Only retry on a subset of service exceptions
if (exception instanceof AmazonServiceException) {
AmazonServiceException ase = (AmazonServiceException)exception;
/*
* For 500 internal server errors and 503 service
* unavailable errors, we want to retry, but we need to use
* an exponential back-off strategy so that we don't overload
* a server with a flood of retries.
*/
if (ase.getStatusCode() == HttpStatus.SC_INTERNAL_SERVER_ERROR
|| ase.getStatusCode() == HttpStatus.SC_SERVICE_UNAVAILABLE) {
return true;
}
/*
* Throttling is reported as a 400 error from newer services. To try
* and smooth out an occasional throttling error, we'll pause and
* retry, hoping that the pause is long enough for the request to
* get through the next time.
*/
if (RetryUtils.isThrottlingException(ase)) return true;
/*
* Clock skew exception. If it is then we will get the time offset
* between the device time and the server time to set the clock skew
* and then retry the request.
*/
if (RetryUtils.isClockSkewError(ase)) return true;
}
return false;
}
}
/** A private class that implements the default back-off strategy. **/
private static class SDKDefaultBackoffStrategy implements RetryPolicy.BackoffStrategy {
/** Base sleep time (milliseconds) for general exceptions. **/
private static final int SCALE_FACTOR = 300;
/** Base sleep time (milliseconds) for throttling exceptions. **/
private static final int THROTTLING_SCALE_FACTOR = 500;
private static final int THROTTLING_SCALE_FACTOR_RANDOM_RANGE = THROTTLING_SCALE_FACTOR / 4;
/** Maximum exponential back-off time before retrying a request */
private static final int MAX_BACKOFF_IN_MILLISECONDS = 20 * 1000;
/** For generating a random scale factor **/
private final Random random = new Random();
/** {@inheritDoc} */
@Override
public final long delayBeforeNextRetry(AmazonWebServiceRequest originalRequest,
AmazonClientException exception,
int retries) {
if (retries <= 0) return 0;
int scaleFactor;
if (exception instanceof AmazonServiceException
&& RetryUtils.isThrottlingException((AmazonServiceException)exception)) {
scaleFactor = THROTTLING_SCALE_FACTOR + random.nextInt(THROTTLING_SCALE_FACTOR_RANDOM_RANGE);
} else {
scaleFactor = SCALE_FACTOR;
}
long delay = (1 << retries) * scaleFactor;
delay = Math.min(delay, MAX_BACKOFF_IN_MILLISECONDS);
return delay;
}
}
/** A private class that implements the default back-off strategy for DynamoDB client. **/
private static class DynamoDBDefaultBackoffStrategy implements RetryPolicy.BackoffStrategy {
/** Base sleep time (milliseconds) **/
private static final int SCALE_FACTOR = 25;
/** Maximum exponential back-off time before retrying a request */
private static final int MAX_BACKOFF_IN_MILLISECONDS = 20 * 1000;
@Override
public final long delayBeforeNextRetry(AmazonWebServiceRequest originalRequest,
AmazonClientException exception,
int retries) {
if (retries <= 0) return 0;
long delay = (1 << retries) * SCALE_FACTOR;
delay = Math.min(delay, MAX_BACKOFF_IN_MILLISECONDS);
return delay;
}
}
}