ARTEMIS-4056 Paging Management optimizations

- optimize startup time on paging (check-depage on startup)
- otpimize getNextPage() on complete pages
- optimize getFirstMessage() and paging. (avoid iterator usage)

artemis-commons/src/main/java/org/apache/activemq/artemis/utils/collections/EmptyList.java

@@ -31,6 +31,10 @@ public class EmptyList<E> implements LinkedList<E> {
    private EmptyList() {
    }
 
+   @Override
+   public E peek() {
+      return null;
+   }
 
    @Override
    public void addHead(E e) {

artemis-commons/src/main/java/org/apache/activemq/artemis/utils/collections/LinkedList.java

@@ -28,6 +28,8 @@ public interface LinkedList<E> {
 
    E poll();
 
+   E peek();
+
    LinkedListIterator<E> iterator();
 
    void clear();

artemis-commons/src/main/java/org/apache/activemq/artemis/utils/collections/LinkedListImpl.java

@@ -103,6 +103,16 @@ public class LinkedListImpl<E> implements LinkedList<E> {
       size++;
    }
 
+   @Override
+   public E peek() {
+      Node<E> current = head.next;
+      if (current == null) {
+         return null;
+      } else {
+         return current.val();
+      }
+   }
+
    @Override
    public E get(int position) {
       Node<E> current = head.next;

artemis-commons/src/main/java/org/apache/activemq/artemis/utils/collections/PriorityLinkedList.java

@@ -31,6 +31,9 @@ public interface PriorityLinkedList<E> {
 
    E poll();
 
+   /** just look at the first element on the list */
+   E peek();
+
    void clear();
 
    /**

artemis-commons/src/main/java/org/apache/activemq/artemis/utils/collections/PriorityLinkedListImpl.java

@@ -126,6 +126,17 @@ public class PriorityLinkedListImpl<E> implements PriorityLinkedList<E> {
       return null;
    }
 
+   @Override
+   public E peek() {
+      for (LinkedListImpl<E> level : levels) {
+         E value = level.peek();
+         if (value != null) {
+            return value;
+         }
+      }
+
+      return null;
+   }
 
    @Override
    public E poll() {

artemis-server/src/main/java/org/apache/activemq/artemis/core/management/impl/QueueControlImpl.java

@@ -874,7 +874,13 @@ public class QueueControlImpl extends AbstractControl implements QueueControl {
       }
    }
 
-   protected Map<String, Object>[] getFirstMessage() throws Exception {
+   /**
+    * this method returns a Map representing the first message.
+    * or null if there's no first message.
+    * @return
+    * @throws Exception
+    */
+   protected Map<String, Object> getFirstMessage() throws Exception {
       if (AuditLogger.isBaseLoggingEnabled()) {
          AuditLogger.getFirstMessage(queue);
       }
@@ -883,16 +889,12 @@ public class QueueControlImpl extends AbstractControl implements QueueControl {
       clearIO();
       try {
          List<Map<String, Object>> messages = new ArrayList<>();
-         queue.flushExecutor();
          final int attributeSizeLimit = addressSettingsRepository.getMatch(address).getManagementMessageAttributeSizeLimit();
-         try (LinkedListIterator<MessageReference> iterator = queue.browserIterator()) {
+         MessageReference firstMessage = queue.peekFirstMessage();
-            // returns just the first, as it's the first only
+         if (firstMessage != null) {
-            if (iterator.hasNext()) {
+            return firstMessage.getMessage().toMap(attributeSizeLimit);
-               MessageReference ref = iterator.next();
+         } else {
-               Message message = ref.getMessage();
+            return null;
-               messages.add(message.toMap(attributeSizeLimit));
-            }
-            return messages.toArray(new Map[1]);
          }
       } finally {
          blockOnIO();
@@ -905,7 +907,8 @@ public class QueueControlImpl extends AbstractControl implements QueueControl {
       if (AuditLogger.isBaseLoggingEnabled()) {
          AuditLogger.getFirstMessageAsJSON(queue);
       }
-      return toJSON(getFirstMessage());
+      Map<String, Object> message = getFirstMessage();
+      return toJSON(message == null ? new Map[0] : new Map[]{message});
    }
 
    @Override
@@ -914,16 +917,17 @@ public class QueueControlImpl extends AbstractControl implements QueueControl {
          AuditLogger.getFirstMessageTimestamp(queue);
       }
 
-      Map<String, Object>[] _message = getFirstMessage();
+      Map<String, Object> message = getFirstMessage();
-      if (_message == null || _message.length == 0 || _message[0] == null) {
+      if (message == null) {
          return null;
-      }
+      } else {
-      Map<String, Object> message = _message[0];
          if (!message.containsKey("timestamp")) {
             return null;
-      }
+         } else {
             return (Long) message.get("timestamp");
          }
+      }
+   }
 
    @Override
    public Long getFirstMessageAge() throws Exception {
@@ -1562,7 +1566,6 @@ public class QueueControlImpl extends AbstractControl implements QueueControl {
 
          ArrayList<CompositeData> c = new ArrayList<>();
          Filter thefilter = FilterImpl.createFilter(filter);
-         queue.flushExecutor();
 
          final int attributeSizeLimit = addressSettingsRepository.getMatch(address).getManagementMessageAttributeSizeLimit();
          try (LinkedListIterator<MessageReference> iterator = queue.browserIterator()) {
@@ -1618,7 +1621,6 @@ public class QueueControlImpl extends AbstractControl implements QueueControl {
          int currentPageSize = 0;
          ArrayList<CompositeData> c = new ArrayList<>();
          Filter thefilter = FilterImpl.createFilter(filter);
-         queue.flushExecutor();
          try (LinkedListIterator<MessageReference> iterator = queue.browserIterator()) {
             try {
                while (iterator.hasNext() && currentPageSize++ < limit) {

artemis-server/src/main/java/org/apache/activemq/artemis/core/paging/cursor/impl/PageSubscriptionImpl.java

@@ -832,13 +832,16 @@ public final class PageSubscriptionImpl implements PageSubscription {
    @Override
    public void processReload() throws Exception {
       if (recoveredACK != null) {
-         logger.trace("********** processing reload!!!!!!!");
+         if (logger.isDebugEnabled()) {
+            logger.debug("processing reload queue name={} with id={}", queue != null ? this.queue.getName() : "N/A", cursorId);
+         }
 
          Collections.sort(recoveredACK);
 
          long txDeleteCursorOnReload = -1;
 
          for (PagePosition pos : recoveredACK) {
+            logger.trace("reloading pos {}", pos);
             lastAckedPosition = pos;
             PageCursorInfo pageInfo = getPageInfo(pos);
             pageInfo.loadACK(pos);
@@ -871,7 +874,7 @@ public final class PageSubscriptionImpl implements PageSubscription {
 
    @Override
    public void onDeletePage(Page deletedPage) throws Exception {
-      logger.trace("removing page {}", deletedPage);
+      logger.debug("removing page {}", deletedPage);
       PageCursorInfo info;
       synchronized (consumedPages) {
          info = consumedPages.remove(Long.valueOf(deletedPage.getPageId()));
@@ -909,6 +912,12 @@ public final class PageSubscriptionImpl implements PageSubscription {
       return getPageInfo(pos.getPageNr());
    }
 
+   public PageCursorInfo locatePageInfo(final long pageNr) {
+      synchronized (consumedPages) {
+         return consumedPages.get(pageNr);
+      }
+   }
+
    public PageCursorInfo getPageInfo(final long pageNr) {
       synchronized (consumedPages) {
          PageCursorInfo pageInfo = consumedPages.get(pageNr);
@@ -1278,11 +1287,20 @@ public final class PageSubscriptionImpl implements PageSubscription {
       private LinkedListIterator<PagedMessage> currentPageIterator;
 
       private void initPage(long page) {
+         if (logger.isDebugEnabled()) {
+            logger.debug("initPage {}", page);
+         }
          try {
             if (currentPage != null) {
+               if (logger.isTraceEnabled()) {
+                  logger.trace("usage down {} on subscription {}", currentPage.getPageId(), cursorId);
+               }
                currentPage.usageDown();
             }
             if (currentPageIterator != null) {
+               if (logger.isTraceEnabled()) {
+                  logger.trace("closing pageIterator on {}", cursorId);
+               }
                currentPageIterator.close();
             }
             currentPage = pageStore.usePage(page);
@@ -1460,23 +1478,47 @@ public final class PageSubscriptionImpl implements PageSubscription {
 
       private PagedReference internalGetNext() {
          for (;;) {
+            assert currentPageIterator != null : "currentPageIterator is null";
             PagedMessage message = currentPageIterator.hasNext() ? currentPageIterator.next() : null;
             logger.trace("CursorIterator::internalGetNext:: new reference {}", message);
             if (message != null) {
                return cursorProvider.newReference(message, PageSubscriptionImpl.this);
             }
 
-            if (currentPage.getPageId() < pageStore.getCurrentWritingPage()) {
             if (logger.isTraceEnabled()) {
-                  logger.trace("CursorIterator::internalGetNext:: moving to currentPage {}", currentPage.getPageId() + 1);
+               logger.trace("Current page {}", currentPage != null ? currentPage.getPageId() : null);
             }
-               initPage(currentPage.getPageId() + 1);
+            long nextPage = getNextPage();
+            if (logger.isTraceEnabled()) {
+               logger.trace("next page {}", nextPage);
+            }
+            if (nextPage >= 0) {
+               if (logger.isTraceEnabled()) {
+                  logger.trace("CursorIterator::internalGetNext:: moving to currentPage {}", nextPage);
+               }
+               initPage(nextPage);
             } else {
                return null;
             }
          }
       }
 
+      private long getNextPage() {
+         long page = currentPage.getPageId() + 1;
+
+         while (page <= pageStore.getCurrentWritingPage()) {
+            PageCursorInfo info = locatePageInfo(page);
+            if (info == null || info.getCompleteInfo() == null) {
+               return page;
+            }
+            if (logger.isDebugEnabled()) {
+               logger.debug("Subscription {} named {}  moving faster from page {} to next", cursorId, queue.getName(), page);
+            }
+            page++;
+         }
+         return -1;
+      }
+
 
       @Override
       public synchronized NextResult tryNext() {

artemis-server/src/main/java/org/apache/activemq/artemis/core/paging/impl/Page.java

@@ -150,9 +150,6 @@ public final class Page  {
    }
 
    public synchronized LinkedList<PagedMessage> read(StorageManager storage, boolean onlyLargeMessages) throws Exception {
-      if (logger.isDebugEnabled()) {
-         logger.debug("reading page {} on address = {} onlyLargeMessages = {}", pageId, storeName, onlyLargeMessages);
-      }
 
       if (!file.isOpen()) {
          if (!file.exists()) {
@@ -161,6 +158,12 @@ public final class Page  {
          throw ActiveMQMessageBundle.BUNDLE.invalidPageIO();
       }
 
+      if (logger.isTraceEnabled()) {
+         logger.trace("reading page {} on address = {} onlyLargeMessages = {}", pageId, storeName, onlyLargeMessages, new Exception("trace"));
+      } else if (logger.isDebugEnabled()) {
+         logger.debug("reading page {} on address = {} onlyLargeMessages = {}", pageId, storeName, onlyLargeMessages);
+      }
+
       size = file.size();
 
       final LinkedList<PagedMessage> messages = new LinkedListImpl<>();

artemis-server/src/main/java/org/apache/activemq/artemis/core/server/Queue.java

@@ -427,6 +427,10 @@ public interface Queue extends Bindable,CriticalComponent {
       }
    }
 
+   default MessageReference peekFirstMessage() {
+      return null;
+   }
+
    LinkedListIterator<MessageReference> browserIterator();
 
    SimpleString getExpiryAddress();

artemis-server/src/main/java/org/apache/activemq/artemis/core/server/impl/QueueImpl.java

@@ -1308,7 +1308,6 @@ public class QueueImpl extends CriticalComponentImpl implements Queue {
    private void deliverAsync(boolean noWait) {
       if (scheduledRunners.get() < MAX_SCHEDULED_RUNNERS) {
          scheduledRunners.incrementAndGet();
-         checkDepage();
          try {
             getExecutor().execute(deliverRunner);
          } catch (RejectedExecutionException ignored) {
@@ -1638,6 +1637,17 @@ public class QueueImpl extends CriticalComponentImpl implements Queue {
       return new QueueBrowserIterator();
    }
 
+   @Override
+   public MessageReference peekFirstMessage() {
+      synchronized (this) {
+         if (messageReferences != null) {
+            return messageReferences.peek();
+         }
+      }
+
+      return null;
+   }
+
    @Override
    public synchronized MessageReference removeReferenceWithID(final long id1) throws Exception {
       try (LinkedListIterator<MessageReference> iterator = iterator()) {
@@ -3164,6 +3174,9 @@ public class QueueImpl extends CriticalComponentImpl implements Queue {
          return;
       }
       if (pageIterator != null && pageSubscription.isPaging()) {
+         if (logger.isDebugEnabled()) {
+            logger.debug("CheckDepage on queue name {}, id={}", name, id);
+         }
          // we will issue a delivery runnable to check for released space from acks and resume depage
          pageDelivered = true;
 

artemis-server/src/test/java/org/apache/activemq/artemis/core/list/PriorityLinkedListTest.java

@@ -878,6 +878,21 @@ public final class PriorityLinkedListTest extends Assert {
    }
 
 
+   @Test
+   public void testPeek() {
+      assertNull(list.peek());
+
+      list.addTail(c, 5);
+      assertEquals(c, list.peek());
+
+      list.addTail(k, 0);
+      assertEquals(k, list.peek());
+
+      list.addHead(a, 0);
+      assertEquals(a, list.peek());
+   }
+
+
    @Test
    public void testRemoveWithID() {
 

tests/unit-tests/src/test/java/org/apache/activemq/artemis/tests/unit/util/LinkedListTest.java

@@ -459,6 +459,25 @@ public class LinkedListTest extends ActiveMQTestBase {
       }
    }
 
+
+   @Test
+   public void testPeek() {
+      assertEquals(0, list.size());
+      assertNull(list.peek());
+      list.addTail(10);
+      assertEquals(10, (int)list.peek());
+      assertEquals(10, (int)list.poll());
+      assertNull(list.peek());
+      list.addTail(12);
+      assertEquals(12, (int)list.peek());
+      list.addHead(5);
+      assertEquals(5, (int)list.peek());
+      list.poll();
+      assertEquals(12, (int)list.peek());
+      list.poll();
+      assertNull(list.peek());
+   }
+
    @Test
    public void testAddHead() {
       int num = 10;