Added 2 new HystrixEventTypes: EMIT and FALLBACK_EMIT.

** These events only get generated in the HystrixObservable case.
** They correspond to an onNext() by construct() and onNext() by resumeWithFallback(), respectively

hystrix-core/src/main/java/com/netflix/hystrix/AbstractCommand.java

@@ -551,27 +551,22 @@ public void call(Notification<? super R> n) {
             }
 
 
-        }).lift(new HystrixObservableTimeoutOperator<>(_self)).map(new Func1<R, R>() {
-
-            boolean once = false;
-
+        }).lift(new HystrixObservableTimeoutOperator<>(_self)).doOnNext(new Action1<R>() {
             @Override
-            public R call(R t1) {
-                if (!once) {
-                    // report success
-                    executionResult = executionResult.addEvents(HystrixEventType.SUCCESS);
-                    once = true;
+            public void call(R r) {
+                if (shouldOutputOnNextEvents()) {
+                    executionResult = executionResult.addEmission(HystrixEventType.EMIT);
+                    eventNotifier.markEvent(HystrixEventType.EMIT, getCommandKey());
                 }
-                return t1;
             }
-
         }).doOnCompleted(new Action0() {
 
             @Override
             public void call() {
                 long duration = System.currentTimeMillis() - invocationStartTime;
                 metrics.addCommandExecutionTime(duration);
                 metrics.markSuccess(duration);
+                executionResult = executionResult.addEvents(HystrixEventType.SUCCESS);
                 circuitBreaker.markSuccess();
                 eventNotifier.markCommandExecution(getCommandKey(), properties.executionIsolationStrategy().get(), (int) duration, executionResult.events);
             }
@@ -781,7 +776,15 @@ private Observable<R> getFallbackOrThrowException(final HystrixEventType eventTy
             executionResult = executionResult.addEvents(eventType);
             final AbstractCommand<R> _cmd = this;
 
-            return getFallbackWithProtection().doOnCompleted(new Action0() {
+            return getFallbackWithProtection().doOnNext(new Action1<R>() {
+                @Override
+                public void call(R r) {
+                    if (shouldOutputOnNextEvents()) {
+                        executionResult = executionResult.addEmission(HystrixEventType.FALLBACK_EMIT);
+                        eventNotifier.markEvent(HystrixEventType.FALLBACK_EMIT, getCommandKey());
+                    }
+                }
+            }).doOnCompleted(new Action0() {
 
                 @Override
                 public void call() {
@@ -886,6 +889,16 @@ protected void handleThreadEnd() {
         }
     }
 
+    /**
+     *
+     * @return if onNext events should be reported on
+     * This affects {@link HystrixRequestLog}, and {@link HystrixEventNotifier} currently.
+     * Metrics/hooks will be affected once they are in place
+     */
+    protected boolean shouldOutputOnNextEvents() {
+        return false;
+    }
+
     private static class HystrixObservableTimeoutOperator<R> implements Operator<R, R> {
 
         final AbstractCommand<R> originalCommand;
@@ -1402,32 +1415,36 @@ protected static class ExecutionResult {
         private final int executionTime;
         private final Exception exception;
         private final long commandRunStartTimeInNanos;
+        private final int numEmissions;
+        private final int numFallbackEmissions;
 
         private ExecutionResult(HystrixEventType... events) {
-            this(Arrays.asList(events), -1, null);
+            this(Arrays.asList(events), -1, null, 0, 0);
         }
 
         public ExecutionResult setExecutionTime(int executionTime) {
-            return new ExecutionResult(events, executionTime, exception);
+            return new ExecutionResult(events, executionTime, exception, numEmissions, numFallbackEmissions);
         }
 
         public ExecutionResult setException(Exception e) {
-            return new ExecutionResult(events, executionTime, e);
+            return new ExecutionResult(events, executionTime, e, numEmissions, numFallbackEmissions);
         }
 
-        private ExecutionResult(List<HystrixEventType> events, int executionTime, Exception e) {
+        private ExecutionResult(List<HystrixEventType> events, int executionTime, Exception e, int numEmissions, int numFallbackEmissions) {
             // we are safe assigning the List reference instead of deep-copying
             // because we control the original list in 'newEvent'
             this.events = events;
             this.executionTime = executionTime;
             if (executionTime >= 0 ) {
-                this.commandRunStartTimeInNanos = System.nanoTime() - this.executionTime*1000*1000; // 1000*1000 will conver the milliseconds to nanoseconds
+                this.commandRunStartTimeInNanos = System.nanoTime() - this.executionTime*1000*1000; // 1000*1000 will convert the milliseconds to nanoseconds
             }
             else {
                 this.commandRunStartTimeInNanos = -1;
             }
             this.exception = e;
 
+            this.numEmissions = numEmissions;
+            this.numFallbackEmissions = numFallbackEmissions;
         }
 
         // we can return a static version since it's immutable
@@ -1440,10 +1457,14 @@ private ExecutionResult(List<HystrixEventType> events, int executionTime, Except
          * @return
          */
         public ExecutionResult addEvents(HystrixEventType... events) {
-            ArrayList<HystrixEventType> newEvents = new ArrayList<>();
-            newEvents.addAll(this.events);
-            Collections.addAll(newEvents, events);
-            return new ExecutionResult(Collections.unmodifiableList(newEvents), executionTime, exception);
+            return new ExecutionResult(getUpdatedList(this.events, events), executionTime, exception, numEmissions, numFallbackEmissions);
+        }
+
+        private static List<HystrixEventType> getUpdatedList(List<HystrixEventType> currentList, HystrixEventType... newEvents) {
+            ArrayList<HystrixEventType> updatedEvents = new ArrayList<>();
+            updatedEvents.addAll(currentList);
+            Collections.addAll(updatedEvents, newEvents);
+            return Collections.unmodifiableList(updatedEvents);
         }
 
         public int getExecutionTime() {
@@ -1456,6 +1477,28 @@ public int getExecutionTime() {
         public Exception getException() {
             return exception;
         }
+
+        /**
+         * This method may be called many times for {@code HystrixEventType.EMIT} and {@link HystrixEventType.FALLBACK_EMIT}.
+         * To save on storage, on the first time we see that event type, it gets added to the event list, and the count gets incremented.
+         * @param eventType emission event
+         * @return "updated" {@link ExecutionResult}
+         */
+        public ExecutionResult addEmission(HystrixEventType eventType) {
+            switch (eventType) {
+                case EMIT: if (events.contains(HystrixEventType.EMIT)) {
+                    return new ExecutionResult(events, executionTime, exception, numEmissions + 1, numFallbackEmissions);
+                } else {
+                    return new ExecutionResult(getUpdatedList(this.events, HystrixEventType.EMIT), executionTime, exception, numEmissions +1, numFallbackEmissions);
+                }
+                case FALLBACK_EMIT: if (events.contains(HystrixEventType.FALLBACK_EMIT)) {
+                    return new ExecutionResult(events, executionTime, exception, numEmissions, numFallbackEmissions + 1);
+                } else {
+                    return new ExecutionResult(getUpdatedList(this.events, HystrixEventType.FALLBACK_EMIT), executionTime, exception, numEmissions, numFallbackEmissions + 1);
+                }
+                default: return this;
+            }
+        }
     }
 
     /* ******************************************************************************** */
@@ -1610,6 +1653,24 @@ public List<HystrixEventType> getExecutionEvents() {
         return executionResult.events;
     }
 
+    /**
+     * Number of emissions of the execution of a command.  Only interesting in the streaming case.
+     * @return number of <code>OnNext</code> emissions by a streaming command
+     */
+    @Override
+    public int getNumberEmissions() {
+        return executionResult.numEmissions;
+    }
+
+    /**
+     * Number of emissions of the execution of a fallback.  Only interesting in the streaming case.
+     * @return number of <code>OnNext</code> emissions by a streaming fallback
+     */
+    @Override
+    public int getNumberFallbackEmissions() {
+        return executionResult.numFallbackEmissions;
+    }
+
     /**
      * The execution time of this command instance in milliseconds, or -1 if not executed.
      * 

hystrix-core/src/main/java/com/netflix/hystrix/HystrixEventType.java

@@ -21,5 +21,5 @@
  * These are most often accessed via {@link HystrixRequestLog} or {@link HystrixCommand#getExecutionEvents()}.
  */
 public enum HystrixEventType {
-    SUCCESS, FAILURE, TIMEOUT, SHORT_CIRCUITED, THREAD_POOL_REJECTED, SEMAPHORE_REJECTED, FALLBACK_SUCCESS, FALLBACK_FAILURE, FALLBACK_REJECTION, EXCEPTION_THROWN, RESPONSE_FROM_CACHE, COLLAPSED, BAD_REQUEST
+    EMIT, SUCCESS, FAILURE, TIMEOUT, SHORT_CIRCUITED, THREAD_POOL_REJECTED, SEMAPHORE_REJECTED, FALLBACK_EMIT, FALLBACK_SUCCESS, FALLBACK_FAILURE, FALLBACK_REJECTION, EXCEPTION_THROWN, RESPONSE_FROM_CACHE, COLLAPSED, BAD_REQUEST
 }

hystrix-core/src/main/java/com/netflix/hystrix/HystrixInvokableInfo.java

@@ -53,6 +53,10 @@ public interface HystrixInvokableInfo<R> {
 
     public List<HystrixEventType> getExecutionEvents();
 
+    public int getNumberEmissions();
+
+    public int getNumberFallbackEmissions();
+
     public int getExecutionTimeInMilliseconds();
 
     public long getCommandRunStartTimeInNanos();

hystrix-core/src/main/java/com/netflix/hystrix/HystrixObservableCommand.java

@@ -20,6 +20,7 @@
 import com.netflix.hystrix.HystrixCommandProperties.ExecutionIsolationStrategy;
 import com.netflix.hystrix.strategy.executionhook.HystrixCommandExecutionHook;
 import com.netflix.hystrix.strategy.properties.HystrixPropertiesStrategy;
+import com.netflix.hystrix.strategy.eventnotifier.HystrixEventNotifier;
 
 /**
  * Used to wrap code that will execute potentially risky functionality (typically meaning a service call over the network)
@@ -49,6 +50,18 @@ protected HystrixObservableCommand(HystrixCommandGroupKey group) {
         this(new Setter(group));
     }
 
+    /**
+     *
+     * Overridden to true so that all onNext emissions are captured
+     *
+     * @return if onNext events should be reported on
+     * This affects {@link HystrixRequestLog}, and {@link HystrixEventNotifier} currently.  Metrics/Hooks later
+     */
+    @Override
+    protected boolean shouldOutputOnNextEvents() {
+        return true;
+    }
+
     /**
      * Construct a {@link HystrixObservableCommand} with defined {@link Setter} that allows injecting property and strategy overrides and other optional arguments.
      * <p>

hystrix-core/src/main/java/com/netflix/hystrix/HystrixRequestLog.java

@@ -150,16 +150,24 @@ public Collection<HystrixInvokableInfo<?>> getAllExecutedCommands() {
      * <li>TestCommand[FAILURE][1ms]</li>
      * <li>TestCommand[THREAD_POOL_REJECTED][1ms]</li>
      * <li>TestCommand[THREAD_POOL_REJECTED, FALLBACK_SUCCESS][1ms]</li>
+     * <li>TestCommand[EMIT, SUCCESS][1ms]</li>
+     * <li>TestCommand[EMITx5, SUCCESS][1ms]</li>
+     * <li>TestCommand[EMITx5, FAILURE, FALLBACK_EMITx6, FALLBACK_FAILURE][100ms]</li>
      * <li>TestCommand[FAILURE, FALLBACK_SUCCESS][1ms], TestCommand[FAILURE, FALLBACK_SUCCESS, RESPONSE_FROM_CACHE][1ms]x4</li>
      * <li>GetData[SUCCESS][1ms], PutData[SUCCESS][1ms], GetValues[SUCCESS][1ms], GetValues[SUCCESS, RESPONSE_FROM_CACHE][1ms], TestCommand[FAILURE, FALLBACK_FAILURE][1ms], TestCommand[FAILURE,
      * FALLBACK_FAILURE, RESPONSE_FROM_CACHE][1ms]</li>
      * </ul>
      * <p>
-     * If a command has a multiplier such as <code>x4</code> that means this command was executed 4 times with the same events. The time in milliseconds is the sum of the 4 executions.
+     * If a command has a multiplier such as <code>x4</code>, that means this command was executed 4 times with the same events. The time in milliseconds is the sum of the 4 executions.
      * <p>
      * For example, <code>TestCommand[SUCCESS][15ms]x4</code> represents TestCommand being executed 4 times and the sum of those 4 executions was 15ms. These 4 each executed the run() method since
      * <code>RESPONSE_FROM_CACHE</code> was not present as an event.
-     * 
+     *
+     * If an EMIT or FALLBACK_EMIT has a multiplier such as <code>x5</code>, that means a <code>HystrixObservableCommand</code> was used and it emitted that number of <code>OnNext</code>s.
+     * <p>
+     * For example, <code>TestCommand[EMITx5, FAILURE, FALLBACK_EMITx6, FALLBACK_FAILURE][100ms]</code> represents TestCommand executing observably, emitted 5 <code>OnNext</code>s, then an <code>OnError</code>.
+     * This command also has an Observable fallback, and it emits 6 <code>OnNext</code>s, then an <code>OnCompleted</code>.
+     *
      * @return String request log or "Unknown" if unable to instead of throwing an exception.
      */
     public String getExecutedCommandsAsString() {
@@ -179,7 +187,26 @@ public String getExecutedCommandsAsString() {
                     //replicate functionality of Arrays.toString(events.toArray()) to append directly to existing StringBuilder
                     builder.append("[");
                     for (HystrixEventType event : events) {
-                        builder.append(event).append(", ");
+                        switch (event) {
+                            case EMIT:
+                                int numEmissions = command.getNumberEmissions();
+                                if (numEmissions > 1) {
+                                    builder.append(event).append("x").append(numEmissions).append(", ");
+                                } else {
+                                    builder.append(event).append(", ");
+                                }
+                                break;
+                            case FALLBACK_EMIT:
+                                int numFallbackEmissions = command.getNumberFallbackEmissions();
+                                if (numFallbackEmissions > 1) {
+                                    builder.append(event).append("x").append(numFallbackEmissions).append(", ");
+                                } else {
+                                    builder.append(event).append(", ");
+                                }
+                                break;
+                            default:
+                                builder.append(event).append(", ");
+                        }
                     }
                     builder.setCharAt(builder.length() - 2, ']');
                     builder.setLength(builder.length() - 1);