Advise not to use polling in real applications

[#165787240]

References #196

Author: acogoluegnes

src/docs/asciidoc/usage-advanced.adoc

@@ -290,6 +290,16 @@ but must be used only in the same Java process. So PerfTest can fall back to `Sy
 which provides only milliseconds precision, but is reliable between different machines
 as long as their clocks are synchronised.
 
+== Asynchronous Consumers vs Synchronous Consumers
+
+Consumers are asynchronous by default in PerfTest. This means they are registered with the AMQP `basic.consume`
+method and the broker pushes messages to them. This is the optimal way to consume messages. PerfTest
+also provides the `--polling` and `--polling-interval` options to consume messages by polling the broker
+with the AMQP `basic.get` method. These options are available to evaluate the performance and the effects
+of `basic.get`, but real applications should avoid using `basic.get` as much as possible because
+it has several drawbacks compared to asynchronous consumers: it needs a network round trip for each message,
+it typically keeps a thread busy for polling in the application, and it intrinsically increases latency.
+
 == TLS Support
 
 PerfTest can use TLS to connect to a node that is

src/main/java/com/rabbitmq/perf/PerfTest.java

@@ -567,7 +567,9 @@ public static Options getOptions() {
         variableSize.setArgs(Option.UNLIMITED_VALUES);
         options.addOption(variableSize);
 
-        options.addOption(new Option("po", "polling",false,"use basic.get to consume messages"));
+        options.addOption(new Option("po", "polling",false,
+                "use basic.get to consume messages. " +
+                "Do not use this in real applications."));
         options.addOption(new Option("pi", "polling-interval",true, "time to wait before polling with basic.get, " +
                 "in millisecond, default is 0."));