Only parse the properties file if special configs exist

This is to minimize the scope of influence exerted by this PR.
In the future, we should make an effort to route all usages of
spark-class through SparkClassLauncher so as to avoid duplicate
logic in bash and Scala.

bin/spark-class

@@ -160,6 +160,7 @@ fi
 # the driver JVM itself.
 
 if [ -n "$SPARK_SUBMIT_CLIENT_MODE" ]; then
+  # This is currently used only if the properties file actually consists of these special configs
   exec "$RUNNER" org.apache.spark.deploy.SparkClassLauncher \
     "$PROPERTIES_FILE" \
     "$RUNNER" \

bin/spark-submit

@@ -42,16 +42,23 @@ DEFAULT_PROPERTIES_FILE="$SPARK_HOME/conf/spark-defaults.conf"
 PROPERTIES_FILE=${PROPERTIES_FILE:-"$DEFAULT_PROPERTIES_FILE"}
 
 # For client mode, the driver will be launched in the same JVM that launches
-# SparkSubmit, so we need to read the properties file for any extra class paths,
-# library paths, java options and memory early on. Otherwise, it will be too
-# late by the time the JVM has started.
+# SparkSubmit, so we may need to read the properties file for any extra class
+# paths, library paths, java options and memory early on. Otherwise, it will
+# be too late by the time the JVM has started.
 
 if [ "$DEPLOY_MODE" == "client" ]; then
   if [ -n "$DRIVER_MEMORY" ]; then
     export SPARK_DRIVER_MEMORY=$DRIVER_MEMORY
   fi
-  export PROPERTIES_FILE
-  export SPARK_SUBMIT_CLIENT_MODE=1
+  # Parse the properties file only if the special configs exist
+  contains_special_configs=$(
+    grep -e "spark.driver.extra*\|spark.driver.memory" "$PROPERTIES_FILE" | \
+    grep -v "^[[:space:]]*#"
+  )
+  if [ -n "$contains_special_configs" ]; then
+    export PROPERTIES_FILE
+    export SPARK_SUBMIT_CLIENT_MODE=1
+  fi
 fi
 
 exec $SPARK_HOME/bin/spark-class org.apache.spark.deploy.SparkSubmit "${ORIG_ARGS[@]}"