Merge pull request quarkusio#47977 from brunobat/HttpServerMetricsTagsContributor

High cardinality warning on HttpServerMetricsTagsContributor.requestContextLocalData()

Author: brunobat

extensions/micrometer/runtime/src/main/java/io/quarkus/micrometer/runtime/HttpServerMetricsTagsContributor.java

@@ -30,6 +30,12 @@ interface Context {
          * however this method is needed because {@link io.smallrye.common.vertx.ContextLocals#get(String)} won't
          * work when {@link HttpServerMetricsTagsContributor#contribute(Context)} is called as the HTTP request has
          * already gone away.
+         * <p>
+         * Beware of high cardinality causing memory usage increase.
+         * <p>
+         * Don't use keys that might hold many different values (more than a few dozens).
+         * The problem is not just about the current request but the combination of different values from all the
+         * requests the server will receive.
          */
         <T> T requestContextLocalData(Object key);
     }