Merge pull request #816 from jeskew/fix/backoff-in-ms-with-jitter

Backoff in MS (not seconds) and throw in some jitter
aws · Nov 7, 2015 · fa6adc0 · fa6adc0
2 parents c275ac7 + f59372c
commit fa6adc0
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Showing 3 changed files with 20 additions and 6 deletions.
diff --git a/src/DynamoDb/DynamoDbClient.php b/src/DynamoDb/DynamoDbClient.php
@@ -78,7 +78,7 @@ public static function _applyRetryConfig($value, array &$args, HandlerList $list
                 RetryMiddleware::createDefaultDecider($value),
                 function ($retries) {
                     return $retries
-                        ? (50 * (int) pow(2, $retries - 1)) / 1000
+                        ? RetryMiddleware::exponentialDelay($retries) / 2
                         : 0;
                 }
             ),

diff --git a/src/RetryMiddleware.php b/src/RetryMiddleware.php
@@ -86,7 +86,7 @@ public static function createDefaultDecider($maxRetries = 3)
      */
     public static function exponentialDelay($retries)
     {
-        return (int) pow(2, $retries - 1);
+        return mt_rand(0, (int) pow(2, $retries - 1) * 100);
     }
 
     /**

diff --git a/tests/RetryMiddlewareTest.php b/tests/RetryMiddlewareTest.php
@@ -82,10 +82,24 @@ public function testDeciderDoesNotRetryAfterMaxAttempts()
     public function testDelaysExponentially()
     {
         $this->assertEquals(0, RetryMiddleware::exponentialDelay(0));
-        $this->assertEquals(1, RetryMiddleware::exponentialDelay(1));
-        $this->assertEquals(2, RetryMiddleware::exponentialDelay(2));
-        $this->assertEquals(4, RetryMiddleware::exponentialDelay(3));
-        $this->assertEquals(8, RetryMiddleware::exponentialDelay(4));
+        $this->assertLessThanOrEqual(100, RetryMiddleware::exponentialDelay(1));
+        $this->assertLessThanOrEqual(200, RetryMiddleware::exponentialDelay(2));
+        $this->assertLessThanOrEqual(400, RetryMiddleware::exponentialDelay(3));
+        $this->assertLessThanOrEqual(800, RetryMiddleware::exponentialDelay(4));
+    }
+
+    public function testDelaysWithSomeRandomness()
+    {
+        $maxDelay = 100 * pow(2, 4);
+        $values = array_map(function () {
+            return RetryMiddleware::exponentialDelay(5);
+        }, range(1, 200));
+
+        $this->assertGreaterThan(1, count(array_unique($values)));
+        foreach ($values as $value) {
+            $this->assertGreaterThanOrEqual(0, $value);
+            $this->assertLessThanOrEqual($maxDelay, $value);
+        }
     }
 
     public function testRetriesWhenResultMatches()