Update HttpClient#metrics(boolean, Function) and HttpServer#metrics(b…

…oolean, Function) javadoc (#2593)

reactor-netty-http/src/main/java/reactor/netty/http/client/HttpClient.java

@@ -62,6 +62,8 @@
 import reactor.netty.tcp.SslProvider;
 import reactor.netty.tcp.TcpClient;
 import reactor.netty.transport.ClientTransport;
+import reactor.util.Logger;
+import reactor.util.Loggers;
 import reactor.util.Metrics;
 import reactor.util.annotation.Nullable;
 
@@ -1158,6 +1160,9 @@ public final HttpClient mapConnect(
 	 * For example instead of using the actual uri {@code "/users/1"} as uri tag value, templated uri
 	 * {@code "/users/{id}"} can be used.
 	 * <p><strong>Note:</strong>
+	 * It is strongly recommended to provide template-like form for the URIs. Without a conversion to a template-like form,
+	 * each distinct URI leads to the creation of a distinct tag, which takes a lot of memory for the metrics.
+	 * <p><strong>Note:</strong>
 	 * It is strongly recommended applications to configure an upper limit for the number of the URI tags.
 	 * For example:
 	 * <pre class="code">
@@ -1180,6 +1185,12 @@ public final HttpClient metrics(boolean enable, Function<String, String> uriTagV
 						"To enable metrics, you must add the dependency `io.micrometer:micrometer-core`" +
 								" to the class path first");
 			}
+			if (uriTagValue == Function.<String>identity()) {
+				log.debug("Metrics are enabled with [uriTagValue=Function#identity]. " +
+						"It is strongly recommended to provide template-like form for the URIs. " +
+						"Without a conversion to a template-like form, each distinct URI leads " +
+						"to the creation of a distinct tag, which takes a lot of memory for the metrics.");
+			}
 			HttpClient dup = duplicate();
 			dup.configuration().metricsRecorder(() -> configuration().defaultMetricsRecorder());
 			dup.configuration().uriTagValue = uriTagValue;
@@ -1582,6 +1593,8 @@ static String reactorNettyVersion() {
 		               .orElse("dev");
 	}
 
+	static final Logger log = Loggers.getLogger(HttpClient.class);
+
 	static final String HTTP_SCHEME = "http";
 
 	static final String HTTPS_SCHEME = "https";

reactor-netty-http/src/main/java/reactor/netty/http/server/HttpServer.java

@@ -577,6 +577,9 @@ public final HttpServer maxKeepAliveRequests(int maxKeepAliveRequests) {
 	 * For example instead of using the actual uri {@code "/users/1"} as uri tag value, templated uri
 	 * {@code "/users/{id}"} can be used.
 	 * <p><strong>Note:</strong>
+	 * It is strongly recommended to provide template-like form for the URIs. Without a conversion to a template-like form,
+	 * each distinct URI leads to the creation of a distinct tag, which takes a lot of memory for the metrics.
+	 * <p><strong>Note:</strong>
 	 * It is strongly recommended applications to configure an upper limit for the number of the URI tags.
 	 * For example:
 	 * <pre class="code">
@@ -599,6 +602,12 @@ public final HttpServer metrics(boolean enable, Function<String, String> uriTagV
 						"To enable metrics, you must add the dependency `io.micrometer:micrometer-core`" +
 								" to the class path first");
 			}
+			if (uriTagValue == Function.<String>identity()) {
+				log.debug("Metrics are enabled with [uriTagValue=Function#identity]. " +
+						"It is strongly recommended to provide template-like form for the URIs. " +
+						"Without a conversion to a template-like form, each distinct URI leads " +
+						"to the creation of a distinct tag, which takes a lot of memory for the metrics.");
+			}
 			HttpServer dup = duplicate();
 			dup.configuration().metricsRecorder(() -> configuration().defaultMetricsRecorder());
 			dup.configuration().uriTagValue = uriTagValue;