[SPARK-19991][CORE][YARN] FileSegmentManagedBuffer performance improvement

## What changes were proposed in this pull request?

Avoid `NoSuchElementException` every time `ConfigProvider.get(val, default)` falls back to default. This apparently causes non-trivial overhead in at least one path, and can easily be avoided.

See https://github.com/apache/spark/pull/17329

## How was this patch tested?

Existing tests

Author: Sean Owen <sowen@cloudera.com>

Closes #17567 from srowen/SPARK-19991.

2 files changed, 12 insertions, 0 deletions

diff --git a/common/network-common/src/main/java/org/apache/spark/network/util/MapConfigProvider.java b/common/network-common/src/main/java/org/apache/spark/network/util/MapConfigProvider.java
index 9cfee7f08d..a2cf87d1af 100644
--- a/common/network-common/src/main/java/org/apache/spark/network/util/MapConfigProvider.java
+++ b/common/network-common/src/main/java/org/apache/spark/network/util/MapConfigProvider.java
@@ -43,6 +43,12 @@ public class MapConfigProvider extends ConfigProvider {
   }
 
   @Override
+  public String get(String name, String defaultValue) {
+    String value = config.get(name);
+    return value == null ? defaultValue : value;
+  }
+
+  @Override
   public Iterable<Map.Entry<String, String>> getAll() {
     return config.entrySet();
   }
diff --git a/common/network-yarn/src/main/java/org/apache/spark/network/yarn/util/HadoopConfigProvider.java b/common/network-yarn/src/main/java/org/apache/spark/network/yarn/util/HadoopConfigProvider.java
index 62a6cca4ed..8beb033699 100644
--- a/common/network-yarn/src/main/java/org/apache/spark/network/yarn/util/HadoopConfigProvider.java
+++ b/common/network-yarn/src/main/java/org/apache/spark/network/yarn/util/HadoopConfigProvider.java
@@ -42,6 +42,12 @@ public class HadoopConfigProvider extends ConfigProvider {
   }
 
   @Override
+  public String get(String name, String defaultValue) {
+    String value = conf.get(name);
+    return value == null ? defaultValue : value;
+  }
+
+  @Override
   public Iterable<Map.Entry<String, String>> getAll() {
     return conf;
   }