Limit processors by available processors

This commit limits the processors setting to be more than the number of
available processors.

Author: jasontedor

docs/reference/migration/migrate_8_0/settings.asciidoc

@@ -11,3 +11,12 @@ provided automatic upgrading of these settings to their `cluster.remote`
 counterparts. In 8.0.0, these settings have been removed. Elasticsearch will
 refuse to start if you have these settings in your configuration or cluster
 state.
+
+[float]
+==== `processors` can no longer exceed the available number of processors
+
+Previously it was possible to set the number of processors used to set the
+default sizes for the thread pools to be more than the number of available
+processors. As this leads to more context switches and more threads but without
+an increase in the number of physical CPUs on which to schedule these additional
+threads, the `processors` setting is now bounded by the number of available processors.

server/src/main/java/org/elasticsearch/common/util/concurrent/EsExecutors.java

@@ -48,26 +48,14 @@
 
 public class EsExecutors {
 
-    private static final DeprecationLogger deprecationLogger = new DeprecationLogger(LogManager.getLogger(EsExecutors.class));
-
     /**
      * Setting to manually set the number of available processors. This setting is used to adjust thread pool sizes per node.
      */
-    public static final Setting<Integer> PROCESSORS_SETTING = new Setting<>(
+    public static final Setting<Integer> PROCESSORS_SETTING = Setting.intSetting(
         "processors",
-        s -> Integer.toString(Runtime.getRuntime().availableProcessors()),
-        s -> {
-            final int value = Setting.parseInt(s, 1, "processors");
-            final int availableProcessors = Runtime.getRuntime().availableProcessors();
-            if (value > availableProcessors) {
-                deprecationLogger.deprecatedAndMaybeLog(
-                    "processors",
-                    "setting processors to value [{}] which is more than available processors [{}] is deprecated",
-                    value,
-                    availableProcessors);
-            }
-            return value;
-        },
+        Runtime.getRuntime().availableProcessors(),
+        1,
+        Runtime.getRuntime().availableProcessors(),
         Property.NodeScope);
 
     /**

server/src/test/java/org/elasticsearch/common/util/concurrent/EsExecutorsTests.java

@@ -32,7 +32,10 @@
 import static org.hamcrest.Matchers.anyOf;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.hasToString;
 import static org.hamcrest.Matchers.lessThan;
+import static org.hamcrest.Matchers.matchesPattern;
+import static org.hamcrest.Matchers.matchesRegex;
 
 /**
  * Tests for EsExecutors and its components like EsAbortPolicy.
@@ -388,4 +391,15 @@ public void testGetTasks() throws InterruptedException {
         }
     }
 
+    public void testProcessorsBound() {
+        final int available = Runtime.getRuntime().availableProcessors();
+        final int processors = randomIntBetween(available + 1, Integer.MAX_VALUE);
+        final Settings settings = Settings.builder().put("processors", processors).build();
+        final IllegalArgumentException e =
+            expectThrows(IllegalArgumentException.class, () -> EsExecutors.PROCESSORS_SETTING.get(settings));
+        assertThat(
+            e,
+            hasToString(containsString("Failed to parse value [" + processors + "] for setting [processors] must be <= " + available)));
+    }
+
 }