adding router numMaxThread configuration for ProxyServlet HttpClient executor

docs/content/Router.md

@@ -56,6 +56,9 @@ druid.router.tierToBrokerMap={"hot":"druid:prod:broker-hot","_default_tier":"dru
 druid.router.http.numConnections=50
 druid.router.http.readTimeout=PT5M
 
+# Number of threads used by the router proxy http client
+druid.router.http.numMaxThreads=100
+
 druid.server.http.numThreads=100
 ```
 

server/src/main/java/io/druid/guice/http/DruidHttpClientConfig.java

@@ -35,6 +35,10 @@ public class DruidHttpClientConfig
   @JsonProperty
   private Period readTimeout = new Period("PT15M");
 
+  @JsonProperty
+  @Min(1)
+  private int numMaxThreads = Math.max(10, (Runtime.getRuntime().availableProcessors() * 17) / 16 + 2) + 30;
+
   public int getNumConnections()
   {
     return numConnections;
@@ -44,4 +48,9 @@ public class DruidHttpClientConfig
   {
     return readTimeout == null ? null : readTimeout.toStandardDuration();
   }
+
+  public int getNumMaxThreads()
+  {
+    return numMaxThreads;
+  }
 }

services/src/main/java/io/druid/cli/RouterJettyServerInitializer.java

@@ -89,7 +89,11 @@ public class RouterJettyServerInitializer implements JettyServerInitializer
         requestLogger
     );
     asyncQueryForwardingServlet.setTimeout(httpClientConfig.getReadTimeout().getMillis());
-    root.addServlet(new ServletHolder(asyncQueryForwardingServlet), "/druid/v2/*");
+    ServletHolder sh = new ServletHolder(asyncQueryForwardingServlet);
+    //NOTE: explicit maxThreads to workaround https://tickets.puppetlabs.com/browse/TK-152
+    sh.setInitParameter("maxThreads", Integer.toString(httpClientConfig.getNumMaxThreads()));
+
+    root.addServlet(sh, "/druid/v2/*");
     JettyServerInitUtils.addExtensionFilters(root, injector);
     root.addFilter(JettyServerInitUtils.defaultAsyncGzipFilterHolder(), "/*", null);
     // Can't use '/*' here because of Guice conflicts with AsyncQueryForwardingServlet path