Emit settings deprecation logging at most once

When a setting is deprecated, if that setting is used repeatedly we
currently emit a deprecation warning every time the setting is used. In
cases like hitting settings endpoints over and over against a node with
a lot of deprecated settings, this can lead to excessive deprecation
warnings which can crush a node. This commit ensures that a given
setting only sees deprecation logging at most once.

Relates #25457

core/src/main/java/org/elasticsearch/common/settings/Setting.java

@@ -345,7 +345,7 @@ public class Setting<T> extends ToXContentToBytes {
     /** Logs a deprecation warning if the setting is deprecated and used. */
     protected void checkDeprecation(Settings settings) {
         // They're using the setting, so we need to tell them to stop
-        if (this.isDeprecated() && this.exists(settings)) {
+        if (this.isDeprecated() && this.exists(settings) && settings.addDeprecatedSetting(this)) {
             // It would be convenient to show its replacement key, but replacement is often not so simple
             final DeprecationLogger deprecationLogger = new DeprecationLogger(Loggers.getLogger(getClass()));
             deprecationLogger.deprecated("[{}] setting was deprecated in Elasticsearch and will be removed in a future release! " +

core/src/main/java/org/elasticsearch/common/settings/Settings.java

@@ -55,7 +55,6 @@ import java.util.Dictionary;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
-import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
@@ -63,6 +62,7 @@ import java.util.NoSuchElementException;
 import java.util.Objects;
 import java.util.Set;
 import java.util.TreeMap;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Function;
 import java.util.function.Predicate;
@@ -93,6 +93,22 @@ public final class Settings implements ToXContent {
     /** The first level of setting names. This is constructed lazily in {@link #names()}. */
     private final SetOnce<Set<String>> firstLevelNames = new SetOnce<>();
 
+    /**
+     * The set of deprecated settings tracked by this settings object.
+     */
+    private final Set<String> deprecatedSettings = Collections.newSetFromMap(new ConcurrentHashMap<>());
+
+    /**
+     * Add the setting as a tracked deprecated setting.
+     *
+     * @param setting the deprecated setting to track
+     * @return true if the setting was not already tracked as a deprecated setting, otherwise false
+     */
+    boolean addDeprecatedSetting(final Setting setting) {
+        assert setting.isDeprecated() && setting.exists(this) : setting.getKey();
+        return deprecatedSettings.add(setting.getKey());
+    }
+
     /**
      * Setting names found in this Settings for both string and secure settings.
      * This is constructed lazily in {@link #keySet()}.

core/src/test/java/org/elasticsearch/common/settings/SettingTests.java

@@ -154,6 +154,22 @@ public class SettingTests extends ESTestCase {
         assertNull(ab2.get());
     }
 
+    public void testDeprecatedSetting() {
+        final Setting<Boolean> deprecatedSetting = Setting.boolSetting("deprecated.foo.bar", false, Property.Deprecated);
+        final Settings settings = Settings.builder().put("deprecated.foo.bar", true).build();
+        final int iterations = randomIntBetween(0, 128);
+        for (int i = 0; i < iterations; i++) {
+            deprecatedSetting.get(settings);
+        }
+        if (iterations > 0) {
+            /*
+             * This tests that we log the deprecation warning exactly one time, otherwise we would have to assert the deprecation warning
+             * for each usage of the setting.
+             */
+            assertSettingDeprecationsAndWarnings(new Setting[]{deprecatedSetting});
+        }
+    }
+
     public void testDefault() {
         TimeValue defaultValue = TimeValue.timeValueMillis(randomIntBetween(0, 1000000));
         Setting<TimeValue> setting =

qa/smoke-test-http/src/test/java/org/elasticsearch/http/DeprecationHttpIT.java

@@ -30,6 +30,7 @@ import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.json.JsonXContent;
 import org.elasticsearch.plugins.Plugin;
+import org.elasticsearch.test.ESIntegTestCase;
 import org.hamcrest.Matcher;
 
 import java.io.IOException;
@@ -54,6 +55,7 @@ import static org.hamcrest.Matchers.hasSize;
 /**
  * Tests {@code DeprecationLogger} uses the {@code ThreadContext} to add response headers.
  */
+@ESIntegTestCase.ClusterScope(scope = ESIntegTestCase.Scope.TEST)
 public class DeprecationHttpIT extends HttpSmokeTestCase {
 
     @Override
@@ -125,14 +127,6 @@ public class DeprecationHttpIT extends HttpSmokeTestCase {
         doTestDeprecationWarningsAppearInHeaders();
     }
 
-    public void testDeprecationHeadersDoNotGetStuck() throws Exception {
-        doTestDeprecationWarningsAppearInHeaders();
-        doTestDeprecationWarningsAppearInHeaders();
-        if (rarely()) {
-            doTestDeprecationWarningsAppearInHeaders();
-        }
-    }
-
     /**
      * Run a request that receives a predictably randomized number of deprecation warnings.
      * <p>