[improve][broker] Don't rollover empty ledgers based on inactivity (#…

…21893)

### Motivation

When `managedLedgerInactiveLedgerRolloverTimeSeconds` is set, let's say to `300` (5 minutes), the ledger will also get rolled in the case when no new entries (messages) were added to the ledger. This doesn't make sense.
Empty ledgers are deleted, but having this extra churn is causing extra load on brokers, bookies, and metadata stores (zookeeper).

### Modifications

Skip rolling the ledger if it is empty.

(cherry picked from commit 49edc3d)

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedLedgerImpl.java

@@ -4460,7 +4460,8 @@ private void cancelScheduledTasks() {
     @Override
     public boolean checkInactiveLedgerAndRollOver() {
         long currentTimeMs = System.currentTimeMillis();
-        if (inactiveLedgerRollOverTimeMs > 0 && currentTimeMs > (lastAddEntryTimeMs + inactiveLedgerRollOverTimeMs)) {
+        if (currentLedgerEntries > 0 && inactiveLedgerRollOverTimeMs > 0 && currentTimeMs > (lastAddEntryTimeMs
+                + inactiveLedgerRollOverTimeMs)) {
             log.info("[{}] Closing inactive ledger, last-add entry {}", name, lastAddEntryTimeMs);
             if (STATE_UPDATER.compareAndSet(this, State.LedgerOpened, State.ClosingLedger)) {
                 LedgerHandle currentLedger = this.currentLedger;

managed-ledger/src/test/java/org/apache/bookkeeper/mledger/impl/ManagedLedgerTest.java

@@ -3898,6 +3898,30 @@ public void testInactiveLedgerRollOver() throws Exception {
         factory.shutdown();
     }
 
+    @Test
+    public void testDontRollOverEmptyInactiveLedgers() throws Exception {
+        int inactiveLedgerRollOverTimeMs = 5;
+        ManagedLedgerFactoryConfig factoryConf = new ManagedLedgerFactoryConfig();
+        @Cleanup("shutdown")
+        ManagedLedgerFactory factory = new ManagedLedgerFactoryImpl(metadataStore, bkc);
+        ManagedLedgerConfig config = new ManagedLedgerConfig();
+        config.setInactiveLedgerRollOverTime(inactiveLedgerRollOverTimeMs, TimeUnit.MILLISECONDS);
+        ManagedLedgerImpl ledger = (ManagedLedgerImpl) factory.open("rollover_inactive", config);
+        ManagedCursor cursor = ledger.openCursor("c1");
+
+        long ledgerId = ledger.currentLedger.getId();
+
+        Thread.sleep(inactiveLedgerRollOverTimeMs * 5);
+        ledger.checkInactiveLedgerAndRollOver();
+
+        Thread.sleep(inactiveLedgerRollOverTimeMs * 5);
+        ledger.checkInactiveLedgerAndRollOver();
+
+        assertEquals(ledger.currentLedger.getId(), ledgerId);
+
+        ledger.close();
+    }
+
     @Test
     public void testOffloadTaskCancelled() throws Exception {
         ManagedLedgerFactory factory = new ManagedLedgerFactoryImpl(metadataStore, bkc);
@@ -4093,6 +4117,7 @@ public void testNonDurableCursorCreateForInactiveLedger() throws Exception {
         ManagedLedgerConfig config = new ManagedLedgerConfig();
         config.setInactiveLedgerRollOverTime(10, TimeUnit.MILLISECONDS);
         ManagedLedgerImpl ml = (ManagedLedgerImpl) factory.open(mlName, config);
+        ml.addEntry("entry".getBytes(UTF_8));
 
         MutableBoolean isRolledOver = new MutableBoolean(false);
         retryStrategically((test) -> {