Avoid tracking the delays of all the message when we detect that they are fixed

pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/DelayedDeliveryTracker.java

@@ -55,6 +55,11 @@ public interface DelayedDeliveryTracker extends AutoCloseable {
      */
     Set<PositionImpl> getScheduledMessages(int maxMessages);
 
+    /**
+     * Tells whether the dispatcher should pause any message deliveries, until the DelayedDeliveryTracker has
+     * more messages available.
+     */
+    boolean shouldPauseAllDeliveries();
 
     /**
      *  Reset tick time use zk policies cache.

pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/InMemoryDelayedDeliveryTracker.java

@@ -55,6 +55,20 @@ public class InMemoryDelayedDeliveryTracker implements DelayedDeliveryTracker, T
 
     private final boolean isDelayedDeliveryDeliverAtTimeStrict;
 
+    // If we detect that all messages have fixed delay time, such that the delivery is
+    // always going to be in FIFO order, then we can avoid pulling all the messages in
+    // tracker. Instead, we use the lookahead for detection and pause the read from
+    // the cursor if the delays are fixed.
+    public static final long DETECT_FIXED_DELAY_LOOKAHEAD_MESSAGES = 50_000;
+
+    // This is the timestamp of the message with the highest delivery time
+    // If new added messages are lower than this, it means the delivery is requested
+    // to be out-of-order. It gets reset to 0, once the tracker is emptied.
+    private long highestDeliveryTimeTracked = 0;
+
+    // Track whether we have seen all messages with fixed delay so far.
+    private boolean messagesHaveFixedDelay = true;
+
     InMemoryDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher, Timer timer, long tickTimeMillis,
                                    boolean isDelayedDeliveryDeliverAtTimeStrict) {
         this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict);
@@ -86,16 +100,28 @@ private long getCutoffTime() {
 
     @Override
     public boolean addMessage(long ledgerId, long entryId, long deliverAt) {
+        if (deliverAt < 0 || deliverAt <= getCutoffTime()) {
+            messagesHaveFixedDelay = false;
+            return false;
+        }
+
         if (log.isDebugEnabled()) {
             log.debug("[{}] Add message {}:{} -- Delivery in {} ms ", dispatcher.getName(), ledgerId, entryId,
                     deliverAt - clock.millis());
         }
-        if (deliverAt <= getCutoffTime()) {
-            return false;
-        }
+
 
         priorityQueue.add(deliverAt, ledgerId, entryId);
         updateTimer();
+
+        // Check that new delivery time comes after the current highest, or at
+        // least within a single tick time interval of 1 second.
+        if (deliverAt < (highestDeliveryTimeTracked - tickTimeMillis)) {
+            messagesHaveFixedDelay = false;
+        }
+
+        highestDeliveryTimeTracked = Math.max(highestDeliveryTimeTracked, deliverAt);
+
         return true;
     }
 
@@ -137,6 +163,13 @@ public Set<PositionImpl> getScheduledMessages(int maxMessages) {
         if (log.isDebugEnabled()) {
             log.debug("[{}] Get scheduled messages - found {}", dispatcher.getName(), positions.size());
         }
+
+        if (priorityQueue.isEmpty()) {
+            // Reset to initial state
+            highestDeliveryTimeTracked = 0;
+            messagesHaveFixedDelay = true;
+        }
+
         updateTimer();
         return positions;
     }
@@ -241,4 +274,12 @@ public void close() {
             timeout.cancel();
         }
     }
+
+    @Override
+    public boolean shouldPauseAllDeliveries() {
+        // Pause deliveries if we know all delays are fixed within the lookahead window
+        return messagesHaveFixedDelay
+                && priorityQueue.size() >= DETECT_FIXED_DELAY_LOOKAHEAD_MESSAGES
+                && !hasMessageAvailable();
+    }
 }

pulsar-broker/src/main/java/org/apache/pulsar/broker/service/AbstractBaseDispatcher.java

@@ -177,8 +177,7 @@ public int filterEntriesForConsumer(Optional<MessageMetadata[]> optMetadataArray
                 entry.release();
                 individualAcknowledgeMessageIfNeeded(pos, Collections.emptyMap());
                 continue;
-            } else if (msgMetadata.hasDeliverAtTime()
-                    && trackDelayedDelivery(entry.getLedgerId(), entry.getEntryId(), msgMetadata)) {
+            } else if (trackDelayedDelivery(entry.getLedgerId(), entry.getEntryId(), msgMetadata)) {
                 // The message is marked for delayed delivery. Ignore for now.
                 entries.set(i, null);
                 entry.release();

pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentDispatcherMultipleConsumers.java

@@ -236,6 +236,10 @@ private synchronized void internalConsumerFlow(Consumer consumer, int additional
     }
 
     public synchronized void readMoreEntries() {
+        if (shouldPauseDeliveryForDelayTracker()) {
+            return;
+        }
+
         // totalAvailablePermits may be updated by other threads
         int firstAvailableConsumerPermits = getFirstAvailableConsumerPermits();
         int currentTotalAvailablePermits = Math.max(totalAvailablePermits, firstAvailableConsumerPermits);
@@ -874,13 +878,20 @@ public boolean trackDelayedDelivery(long ledgerId, long entryId, MessageMetadata
 
         synchronized (this) {
             if (!delayedDeliveryTracker.isPresent()) {
+                if (!msgMetadata.hasDeliverAtTime()) {
+                    // No need to initialize the tracker here
+                    return false;
+                }
+
                 // Initialize the tracker the first time we need to use it
                 delayedDeliveryTracker = Optional
                         .of(topic.getBrokerService().getDelayedDeliveryTrackerFactory().newTracker(this));
             }
 
             delayedDeliveryTracker.get().resetTickTime(topic.getDelayedDeliveryTickTimeMillis());
-            return delayedDeliveryTracker.get().addMessage(ledgerId, entryId, msgMetadata.getDeliverAtTime());
+
+            long deliverAtTime = msgMetadata.hasDeliverAtTime() ? msgMetadata.getDeliverAtTime() : -1L;
+            return delayedDeliveryTracker.get().addMessage(ledgerId, entryId, deliverAtTime);
         }
     }
 
@@ -895,6 +906,10 @@ protected synchronized Set<PositionImpl> getMessagesToReplayNow(int maxMessagesT
         }
     }
 
+    protected synchronized boolean shouldPauseDeliveryForDelayTracker() {
+        return delayedDeliveryTracker.isPresent() && delayedDeliveryTracker.get().shouldPauseAllDeliveries();
+    }
+
     @Override
     public synchronized long getNumberOfDelayedMessages() {
         return delayedDeliveryTracker.map(DelayedDeliveryTracker::getNumberOfDelayedMessages).orElse(0L);

pulsar-broker/src/test/java/org/apache/pulsar/broker/delayed/InMemoryDeliveryTrackerTest.java

@@ -314,4 +314,117 @@ public void testAddMessageWithDeliverAtTimeAfterFullTickTimeWithStrict() throws
         Awaitility.await().atMost(10, TimeUnit.SECONDS)
                 .untilAsserted(() -> verify(dispatcher).readMoreEntries());
     }
+
+    @Test
+    public void testWithFixedDelays() throws Exception {
+        PersistentDispatcherMultipleConsumers dispatcher = mock(PersistentDispatcherMultipleConsumers.class);
+
+        AtomicLong clockTime = new AtomicLong();
+        Clock clock = mock(Clock.class);
+        when(clock.millis()).then(x -> clockTime.get());
+
+        @Cleanup
+        InMemoryDelayedDeliveryTracker tracker = new InMemoryDelayedDeliveryTracker(dispatcher, timer, 1, clock,
+                true);
+
+        assertFalse(tracker.hasMessageAvailable());
+
+        assertTrue(tracker.addMessage(1, 1, 10));
+        assertTrue(tracker.addMessage(2, 2, 20));
+        assertTrue(tracker.addMessage(3, 3, 30));
+        assertTrue(tracker.addMessage(4, 4, 40));
+        assertTrue(tracker.addMessage(5, 5, 50));
+
+        assertFalse(tracker.hasMessageAvailable());
+        assertEquals(tracker.getNumberOfDelayedMessages(), 5);
+        assertFalse(tracker.shouldPauseAllDeliveries());
+
+        for (int i = 6; i <= InMemoryDelayedDeliveryTracker.DETECT_FIXED_DELAY_LOOKAHEAD_MESSAGES; i++) {
+            assertTrue(tracker.addMessage(i, i, i * 10));
+        }
+
+        assertTrue(tracker.shouldPauseAllDeliveries());
+
+        clockTime.set(InMemoryDelayedDeliveryTracker.DETECT_FIXED_DELAY_LOOKAHEAD_MESSAGES * 10);
+
+        tracker.getScheduledMessages(100);
+        assertFalse(tracker.shouldPauseAllDeliveries());
+
+        // Empty the tracker
+        int removed = 0;
+        do {
+            removed = tracker.getScheduledMessages(100).size();
+        } while (removed > 0);
+
+        assertFalse(tracker.shouldPauseAllDeliveries());
+    }
+
+    @Test
+    public void testWithMixedDelays() throws Exception {
+        PersistentDispatcherMultipleConsumers dispatcher = mock(PersistentDispatcherMultipleConsumers.class);
+
+        AtomicLong clockTime = new AtomicLong();
+        Clock clock = mock(Clock.class);
+        when(clock.millis()).then(x -> clockTime.get());
+
+        @Cleanup
+        InMemoryDelayedDeliveryTracker tracker = new InMemoryDelayedDeliveryTracker(dispatcher, timer, 1, clock,
+                true);
+
+        assertFalse(tracker.hasMessageAvailable());
+
+        assertTrue(tracker.addMessage(1, 1, 10));
+        assertTrue(tracker.addMessage(2, 2, 20));
+        assertTrue(tracker.addMessage(3, 3, 30));
+        assertTrue(tracker.addMessage(4, 4, 40));
+        assertTrue(tracker.addMessage(5, 5, 50));
+
+        assertFalse(tracker.shouldPauseAllDeliveries());
+
+        for (int i = 6; i <= InMemoryDelayedDeliveryTracker.DETECT_FIXED_DELAY_LOOKAHEAD_MESSAGES; i++) {
+            assertTrue(tracker.addMessage(i, i, i * 10));
+        }
+
+        assertTrue(tracker.shouldPauseAllDeliveries());
+
+        // Add message with earlier delivery time
+        assertTrue(tracker.addMessage(5, 5, 5));
+
+        assertFalse(tracker.shouldPauseAllDeliveries());
+    }
+
+    @Test
+    public void testWithNoDelays() throws Exception {
+        PersistentDispatcherMultipleConsumers dispatcher = mock(PersistentDispatcherMultipleConsumers.class);
+
+        AtomicLong clockTime = new AtomicLong();
+        Clock clock = mock(Clock.class);
+        when(clock.millis()).then(x -> clockTime.get());
+
+        @Cleanup
+        InMemoryDelayedDeliveryTracker tracker = new InMemoryDelayedDeliveryTracker(dispatcher, timer, 1, clock,
+                true);
+
+        assertFalse(tracker.hasMessageAvailable());
+
+        assertTrue(tracker.addMessage(1, 1, 10));
+        assertTrue(tracker.addMessage(2, 2, 20));
+        assertTrue(tracker.addMessage(3, 3, 30));
+        assertTrue(tracker.addMessage(4, 4, 40));
+        assertTrue(tracker.addMessage(5, 5, 50));
+
+        assertFalse(tracker.shouldPauseAllDeliveries());
+
+        for (int i = 6; i <= InMemoryDelayedDeliveryTracker.DETECT_FIXED_DELAY_LOOKAHEAD_MESSAGES; i++) {
+            assertTrue(tracker.addMessage(i, i, i * 10));
+        }
+
+        assertTrue(tracker.shouldPauseAllDeliveries());
+
+        // Add message with no-delay
+        assertFalse(tracker.addMessage(5, 5, -1L));
+
+        assertFalse(tracker.shouldPauseAllDeliveries());
+    }
+
 }