NMS-15738: enable asynchronous polling by default

docs/modules/operation/pages/deep-dive/service-assurance/configuration.adoc

@@ -62,29 +62,12 @@ During evaluation of an expression, the following scopes are available:
 [[ga-pollerd-configuration-async]]
 == Asynchronous engine
 
-By default, the number of polls active at any given time is limited by the number of threads that are allocated to pollerd.
-Each thread is responsible for one poll, and will block until the poll is completed; this is true even when the polling is done by a Minion at a remote location.
-In this case, the thread is blocked for the duration of the remote procedure call.
+By default, the asynchronous polling engine is enabled.
+It allows threads to be released while polls are active, enabling processing more polls than the number of threads available.
 
-If you have hundreds of locations and hundreds of nodes at each location, you may want to reduce the number of threads required on your {page-component-title} instance.
-Each thread allocates a fixed amount of system memory.
-Having too many threads active at a given time can cause extensive load on the system.
+In the older legacy implementation, the number of polls active at any given time was limited by the number of threads allocated to pollerd.
+Each thread was responsible for one poll, and blocked until the poll was completed; this was true even when the polling was done by a Minion at a remote location.
 
-When enabled, the asynchronous polling mode mitigates this load.
-It allows threads to be released while polls are active, enabling Minions to process more polls than the number of threads available.
+If you wish to revert to the legacy thread model, disable it by setting `asyncPollingEnabled="false" in `etc/poller-configuration.xml`.
 
-To enable the feature, set the following attributes in the top-level element of `etc/poller-configuration.xml`:
-
-[source, xml]
-----
-<poller-configuration threads="30"
-                      asyncPollingEngineEnabled="true" <1>
-                      maxConcurrentAsyncPolls="200" <2>
-----
-<1> Enables the asynchronous polling engine.
-<2> Used to limit the number of polls active, since each of these still consumes some memory resources.
-
-In this mode, threads are used only to trigger a poll to run; this means that the number of threads can typically be reduced.
-You can see the actual number of active (in-flight) polls by reviewing the `NumPollsInFlight` metrics associated with pollerd's MBeans.
-
-NOTE: To disable asynchronous polling, set `asyncPollingEngineEnabled` to false.
+You can query the actual number of active (in-flight) polls by reviewing the `NumPollsInFlight` metrics associated with pollerd's MBeans.

opennms-base-assembly/src/main/filtered/etc/poller-configuration.xml

@@ -1,4 +1,10 @@
-<poller-configuration xmlns="http://xmlns.opennms.org/xsd/config/poller" threads="30" nextOutageId="SELECT nextval('outageNxtId')" serviceUnresponsiveEnabled="false" pathOutageEnabled="false">
+<poller-configuration xmlns="http://xmlns.opennms.org/xsd/config/poller"
+      threads="30"
+      asyncPollingEngineEnabled="true"
+      maxConcurrentAsyncPolls="200"
+      nextOutageId="SELECT nextval('outageNxtId')"
+      serviceUnresponsiveEnabled="false"
+      pathOutageEnabled="false">
    <node-outage status="on" pollAllIfNoCriticalServiceDefined="true">
       <critical-service name="ICMP"/>
    </node-outage>