address comments

velox/connectors/hive/storage_adapters/s3fs/S3FileSystem.cpp

@@ -564,7 +564,9 @@ class S3FileSystem::Impl {
     }
 
     auto retryStrategy = getRetryStrategy();
-    clientConfig.retryStrategy = retryStrategy;
+    if (retryStrategy.has_value()) {
+      clientConfig.retryStrategy = retryStrategy.value();
+    }
 
     auto credentialsProvider = getCredentialsProvider();
 
@@ -645,7 +647,8 @@ class S3FileSystem::Impl {
   }
 
   // Return a client RetryStrategy based on the config.
-  std::shared_ptr<Aws::Client::RetryStrategy> getRetryStrategy() const {
+  std::optional<std::shared_ptr<Aws::Client::RetryStrategy>> getRetryStrategy()
+      const {
     auto retryMode = hiveConfig_->s3RetryMode();
     auto maxAttempts = hiveConfig_->s3MaxAttempts();
     if (retryMode.has_value()) {
@@ -671,10 +674,22 @@ class S3FileSystem::Impl {
           // Otherwise, use default value 3.
           return std::make_shared<Aws::Client::AdaptiveRetryStrategy>();
         }
+      } else if (retryMode.value() == "legacy") {
+        if (maxAttempts.has_value()) {
+          VELOX_USER_CHECK(
+              (maxAttempts.value() > 0),
+              "Invalid configuration: specify 'max-attempts' > 0.");
+          return std::make_shared<Aws::Client::DefaultRetryStrategy>(
+              maxAttempts.value());
+        } else {
+          // Otherwise, use default value maxRetries = 10, scaleFactor = 25
+          return std::make_shared<Aws::Client::DefaultRetryStrategy>();
+        }
+      } else {
+        VELOX_USER_FAIL("Invalid retry mode for S3: {}", retryMode.value());
       }
     }
-    // By default use DefaultRetryStrategy.
-    return std::make_shared<Aws::Client::DefaultRetryStrategy>();
+    return std::nullopt;
   }
 
   // Make it clear that the S3FileSystem instance owns the S3Client.

velox/docs/configs.rst

@@ -539,11 +539,14 @@ Each query can override the config by setting corresponding query session proper
    * - hive.s3.max-attempts
      - integer
      -
-     - Maximum attempts for connections to a single http client.
+     - Maximum attempts for connections to a single http client, work together with retry-mode. By default, it's 3 for standard/adaptive mode
+       and 10 for legacy mode.
    * - hive.s3.retry-mode
      - string
      -
-     - 'standard' or 'adaptive', use DefaultRetryStrategy if it's empty.
+     - **Allowed values:** "standard", "adaptive", "legacy". By default use legacy mode, which only enables throttled retry for transient errors.
+       Standard mode is built on top of legacy mode and has throttled retry enabled for throttling errors apart from transient errors.
+       Adaptive retry mode dynamically limits the rate of AWS requests to maximize success rate. 
 ``Google Cloud Storage Configuration``
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 .. list-table::