Add sanity check in GC to prevent active ledger deletion

bookkeeper-server/pom.xml

@@ -59,6 +59,12 @@
       <version>4.8.1</version>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-all</artifactId>
+      <version>1.10.19</version>
+      <scope>test</scope>
+    </dependency>
     <dependency>
       <groupId>org.slf4j</groupId>
       <artifactId>slf4j-api</artifactId>

bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/ScanAndCompareGarbageCollector.java

@@ -27,6 +27,7 @@
 import java.util.SortedMap;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.Semaphore;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.apache.bookkeeper.bookie.GarbageCollectorThread.CompactableLedgerStorage;
 import org.apache.bookkeeper.client.BKException;
@@ -87,13 +88,13 @@ public void gc(GarbageCleaner garbageCleaner) {
             // Get a set of all ledgers on the bookie
             NavigableSet<Long> bkActiveLedgers = Sets.newTreeSet(ledgerStorage.getActiveLedgersInRange(0, Long.MAX_VALUE));
 
+            Semaphore semaphore = new Semaphore(MAX_CONCURRENT_ZK_REQUESTS);
             // Iterate over all the ledger on the metadata store
             LedgerRangeIterator ledgerRangeIterator = ledgerManager.getLedgerRanges();
-
             if (!ledgerRangeIterator.hasNext()) {
                 // Empty global active ledgers, need to remove all local active ledgers.
                 for (long ledgerId : bkActiveLedgers) {
-                    garbageCleaner.clean(ledgerId);
+                    gcLedgerSafely(garbageCleaner, ledgerId, ledgerManager, semaphore);
                 }
             }
 
@@ -127,7 +128,7 @@ public void gc(GarbageCleaner garbageCleaner) {
                 }
                 for (Long bkLid : subBkActiveLedgers) {
                     if (!ledgersInMetadata.contains(bkLid)) {
-                        garbageCleaner.clean(bkLid);
+                        gcLedgerSafely(garbageCleaner, bkLid, ledgerManager, semaphore);
                     }
                 }
                 lastEnd = end;
@@ -138,6 +139,38 @@ public void gc(GarbageCleaner garbageCleaner) {
         }
     }
 
+    /**
+     * Cleans ledger safely by verifying ledger-metadata is deleted from the zk else it skips ledger-gc if ledger-metada
+     * exists in zk.
+     * 
+     * @param garbageCleaner
+     * @param ledgerId
+     * @param ledgerManager
+     * @param semaphore
+     * @throws InterruptedException
+     */
+    private void gcLedgerSafely(GarbageCleaner garbageCleaner, long ledgerId, LedgerManager ledgerManager,
+            Semaphore semaphore) throws InterruptedException {
+        semaphore.acquire();
+        CountDownLatch latch = new CountDownLatch(1);
+        AtomicBoolean ledgerDeleted = new AtomicBoolean(false);
+        ledgerManager.existLedgerMetadata(ledgerId, (rc, exists) -> {
+            if (rc == BKException.Code.NoSuchLedgerExistsException) {
+                ledgerDeleted.set(true);
+            } else if (rc == BKException.Code.OK) {
+                LOG.warn("Can't delete ledger {} with metadata exists in zk ", ledgerId);
+            } else {
+                LOG.warn("Fail to check {} exists in zk {}", ledgerId, BKException.getMessage(rc));
+            }
+            latch.countDown();
+            semaphore.release();
+        });
+        latch.await();
+        if (ledgerDeleted.get()) {
+            garbageCleaner.clean(ledgerId);
+        }
+    }
+
     private Set<Long> removeOverReplicatedledgers(Set<Long> bkActiveledgers, GarbageCleaner garbageCleaner)
             throws InterruptedException, KeeperException {
         Set<Long> overReplicatedLedgers = Sets.newHashSet();

bookkeeper-server/src/main/java/org/apache/bookkeeper/meta/AbstractZkLedgerManager.java

@@ -22,7 +22,6 @@
 import java.util.List;
 import java.util.NavigableSet;
 import java.util.Set;
-import java.util.TreeSet;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.Executors;
@@ -37,7 +36,6 @@
 import org.apache.bookkeeper.proto.BookkeeperInternalCallbacks.MultiCallback;
 import org.apache.bookkeeper.proto.BookkeeperInternalCallbacks.Processor;
 import org.apache.bookkeeper.util.BookKeeperConstants;
-import org.apache.bookkeeper.util.StringUtils;
 import org.apache.bookkeeper.util.ZkUtils;
 import org.apache.bookkeeper.versioning.Version;
 import org.apache.zookeeper.AsyncCallback;
@@ -350,6 +348,23 @@ public void readLedgerMetadata(final long ledgerId, final GenericCallback<Ledger
         readLedgerMetadata(ledgerId, readCb, null);
     }
 
+    @Override
+    public void existLedgerMetadata(final long ledgerId, final GenericCallback<Boolean> callback) {
+        zk.exists(getLedgerPath(ledgerId), false, (int rc, String path, Object ctx, Stat stat) -> {
+            if (rc == KeeperException.Code.NONODE.intValue()) {
+                callback.operationComplete(BKException.Code.NoSuchLedgerExistsException, false);
+                return;
+            } else if (rc != KeeperException.Code.OK.intValue()) {
+                LOG.error("Could not check metadata exists for ledger: " + ledgerId,
+                        KeeperException.create(KeeperException.Code.get(rc), path));
+                callback.operationComplete(BKException.Code.ZKException, false);
+                return;
+            } else {
+                callback.operationComplete(BKException.Code.OK, true);
+            }
+        }, null);
+    }
+
     protected void readLedgerMetadata(final long ledgerId, final GenericCallback<LedgerMetadata> readCb,
                                       Watcher watcher) {
         zk.getData(getLedgerPath(ledgerId), watcher, new DataCallback() {

bookkeeper-server/src/main/java/org/apache/bookkeeper/meta/CleanupLedgerManager.java

@@ -143,6 +143,20 @@ public void readLedgerMetadata(long ledgerId,
         }
     }
 
+    @Override
+    public void existLedgerMetadata(final long ledgerId, final GenericCallback<Boolean> callback) {
+        closeLock.readLock().lock();
+        try {
+            if (closed) {
+                callback.operationComplete(BKException.Code.ClientClosedException, false);
+                return;
+            }
+            underlying.existLedgerMetadata(ledgerId, new CleanupGenericCallback<Boolean>(callback));
+        } finally {
+            closeLock.readLock().unlock();
+        }
+    }
+
     @Override
     public void writeLedgerMetadata(long ledgerId, LedgerMetadata metadata,
                                     GenericCallback<Void> cb) {

bookkeeper-server/src/main/java/org/apache/bookkeeper/meta/LedgerManager.java

@@ -89,6 +89,20 @@ public interface LedgerManager extends Closeable {
      */
     public void readLedgerMetadata(long ledgerId, GenericCallback<LedgerMetadata> readCb);
 
+    /**
+     * Check ledger metadata exists for a specified ledger.
+     *
+     * @param ledgerId
+     *          Ledger Id
+     * @param readCb
+     *          Callback when read ledger metadata. Return code:<ul>
+     *          <li>{@link BKException.Code.OK} if success</li>
+     *          <li>{@link BKException.Code.NoSuchLedgerExistsException} if ledger not exist</li>
+     *          <li>{@link BKException.Code.ZKException} for other issue</li>
+     *          </ul>
+     */
+    void existLedgerMetadata(long ledgerId, GenericCallback<Boolean> callback);
+
     /**
      * Write ledger metadata.
      *

bookkeeper-server/src/main/java/org/apache/bookkeeper/meta/MSLedgerManagerFactory.java

@@ -420,6 +420,30 @@ public void complete(int rc, Versioned<Value> value, Object ctx) {
             ledgerTable.get(key, this, msCallback, ALL_FIELDS);
         }
 
+        @Override
+        public void existLedgerMetadata(final long ledgerId, final GenericCallback<Boolean> callback) {
+            final String key = ledgerId2Key(ledgerId);
+            MetastoreCallback<Versioned<Value>> msCallback = new MetastoreCallback<Versioned<Value>>() {
+                @Override
+                public void complete(int rc, Versioned<Value> value, Object ctx) {
+                    if (MSException.Code.NoKey.getCode() == rc) {
+                        LOG.error("No ledger metadata found for ledger " + ledgerId + " : ",
+                                MSException.create(MSException.Code.get(rc), "No key " + key + " found."));
+                        callback.operationComplete(BKException.Code.NoSuchLedgerExistsException, false);
+                        return;
+                    } else if (MSException.Code.OK.getCode() != rc) {
+                        LOG.error("Could not read metadata for ledger " + ledgerId + " : ",
+                                MSException.create(MSException.Code.get(rc), "Failed to get key " + key));
+                        callback.operationComplete(BKException.Code.MetaStoreException, false);
+                        return;
+                    } else {
+                        callback.operationComplete(BKException.Code.OK, true);
+                    }
+                }
+            };
+            ledgerTable.get(key, this, msCallback, ALL_FIELDS);
+        }
+
         @Override
         public void writeLedgerMetadata(final long ledgerId, final LedgerMetadata metadata,
                 final GenericCallback<Void> cb) {

bookkeeper-server/src/test/java/org/apache/bookkeeper/bookie/CompactionTest.java

@@ -528,6 +528,10 @@ public LedgerManager.LedgerRange next() throws IOException {
                         }
                     };
                  }
+                @Override
+                public void existLedgerMetadata(long ledgerId, GenericCallback<Boolean> callback) {
+                    unsupported();
+                }
             };
         }
 

bookkeeper-server/src/test/java/org/apache/bookkeeper/meta/GcLedgersTest.java

@@ -53,9 +53,12 @@
 import org.apache.bookkeeper.proto.BookkeeperInternalCallbacks.GenericCallback;
 import org.apache.bookkeeper.versioning.Version;
 import org.junit.Test;
+import org.mockito.Mockito;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import com.google.common.collect.Sets;
+
 /**
  * Test garbage collection ledgers in ledger manager
  */
@@ -300,4 +303,64 @@ public void clean(long ledgerId) {
         assertEquals("Should have cleaned something", 1, cleaned.size());
         assertEquals("Should have cleaned first ledger" + first, (long) first, (long) cleaned.get(0));
     }
+
+    /**
+     * It verifies that GC doesn't delete ledgers which are not deleted and its metadata present into zookeeper even
+     * though ledgerManager derives active ledger as deleted.
+     * 
+     * <pre>
+     *  1. Create list of ledgers
+     *  2. Mock ledgerManager that derives live ledgers as deleted ledgers
+     *  3. GC performs sanity before deleting ledger and doesn't delete if ledger metadata present
+     * </pre>
+     * 
+     * @throws Exception
+     */
+    @Test(timeout = 120000)
+    public void testGCTryToDeleteActiveLedgers() throws Exception {
+        final SortedSet<Long> createdLedgers = Collections.synchronizedSortedSet(new TreeSet<Long>());
+        final List<Long> cleaned = new ArrayList<Long>();
+
+        final int numLedgers = 100;
+
+        createLedgers(numLedgers, createdLedgers);
+
+        LedgerManager ledgerManager = Mockito.spy(getLedgerManager());
+        LedgerRange range = new LedgerRange(Sets.newHashSet(createdLedgers.first()));
+        AtomicInteger noOfIterations = new AtomicInteger(1);
+
+        LedgerRangeIterator ledgerRangeIterator = new LedgerRangeIterator() {
+            @Override
+            public boolean hasNext() throws IOException {
+                return noOfIterations.get() > 0;
+            }
+
+            @Override
+            public LedgerRange next() throws IOException {
+                noOfIterations.decrementAndGet();
+                return range;
+            }
+        };
+
+        Mockito.doReturn(ledgerRangeIterator).when(ledgerManager).getLedgerRanges();
+
+        final GarbageCollector garbageCollector = new ScanAndCompareGarbageCollector(ledgerManager,
+                new MockLedgerStorage(), null, null, false, baseConf.getZkLedgersRootPath());
+        GarbageCollector.GarbageCleaner cleaner = new GarbageCollector.GarbageCleaner() {
+            @Override
+            public void clean(long ledgerId) {
+                LOG.info("Cleaned {}", ledgerId);
+                cleaned.add(ledgerId);
+            }
+        };
+
+        garbageCollector.gc(cleaner);
+        assertTrue("Should have cleaned nothing", cleaned.isEmpty());
+
+        long first = createdLedgers.first();
+        removeLedger(first);
+        garbageCollector.gc(cleaner);
+        assertEquals("Should have cleaned something", 1, cleaned.size());
+        assertEquals("Should have cleaned first ledger" + first, (long) first, (long) cleaned.get(0));
+    }
 }