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

2 files changed, 18 insertions, 2 deletions

diff --git a/core/src/main/java/org/elasticsearch/common/settings/Setting.java b/core/src/main/java/org/elasticsearch/common/settings/Setting.java
index d81204cfb2..241315144a 100644
--- a/core/src/main/java/org/elasticsearch/common/settings/Setting.java
+++ b/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! " +
diff --git a/core/src/main/java/org/elasticsearch/common/settings/Settings.java b/core/src/main/java/org/elasticsearch/common/settings/Settings.java
index 182ea6ccb1..8412f57fd8 100644
--- a/core/src/main/java/org/elasticsearch/common/settings/Settings.java
+++ b/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;
@@ -94,6 +94,22 @@ public final class Settings implements ToXContent {
     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()}.
      */