liangyepianzhou commented on code in PR #18273:
URL: https://github.com/apache/pulsar/pull/18273#discussion_r1099973516


##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/transaction/buffer/impl/SnapshotSegmentAbortedTxnProcessorImpl.java:
##########
@@ -0,0 +1,758 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.transaction.buffer.impl;
+
+import io.netty.buffer.ByteBuf;
+import io.netty.buffer.Unpooled;
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ConcurrentLinkedDeque;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
+import java.util.function.Supplier;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.AsyncCallbacks;
+import org.apache.bookkeeper.mledger.Entry;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.ManagedLedgerImpl;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.bookkeeper.mledger.impl.ReadOnlyManagedLedgerImpl;
+import org.apache.commons.collections4.map.LinkedMap;
+import org.apache.commons.lang3.tuple.MutablePair;
+import org.apache.commons.lang3.tuple.Pair;
+import org.apache.pulsar.broker.service.BrokerServiceException;
+import org.apache.pulsar.broker.service.persistent.PersistentTopic;
+import org.apache.pulsar.broker.systopic.SystemTopicClient;
+import org.apache.pulsar.broker.transaction.buffer.AbortedTxnProcessor;
+import 
org.apache.pulsar.broker.transaction.buffer.metadata.v2.TransactionBufferSnapshotIndex;
+import 
org.apache.pulsar.broker.transaction.buffer.metadata.v2.TransactionBufferSnapshotIndexes;
+import 
org.apache.pulsar.broker.transaction.buffer.metadata.v2.TransactionBufferSnapshotIndexesMetadata;
+import 
org.apache.pulsar.broker.transaction.buffer.metadata.v2.TransactionBufferSnapshotSegment;
+import org.apache.pulsar.broker.transaction.buffer.metadata.v2.TxnIDData;
+import org.apache.pulsar.client.api.Message;
+import org.apache.pulsar.client.api.Schema;
+import org.apache.pulsar.client.api.transaction.TxnID;
+import org.apache.pulsar.client.impl.MessageIdImpl;
+import org.apache.pulsar.client.impl.PulsarClientImpl;
+import org.apache.pulsar.common.naming.SystemTopicNames;
+import org.apache.pulsar.common.naming.TopicDomain;
+import org.apache.pulsar.common.naming.TopicName;
+import org.apache.pulsar.common.protocol.Commands;
+import org.apache.pulsar.common.util.FutureUtil;
+
+@Slf4j
+public class SnapshotSegmentAbortedTxnProcessorImpl implements 
AbortedTxnProcessor {
+
+    /**
+     * Stored the unsealed aborted transaction IDs Whose size is always less 
than the snapshotSegmentCapacity.
+     * It will be persistent as a snapshot segment when its size reach the 
configured capacity.
+     */
+    private LinkedList<TxnID> unsealedTxnIds;
+
+    /**
+     * The map is used to clear the aborted transaction IDs persistent in the 
expired ledger.
+     * <p>
+     *     The key PositionImpl {@link PositionImpl} is the persistent 
position of
+     *     the latest transaction of a segment.
+     *     The value TxnID {@link TxnID} is the latest Transaction ID in a 
segment.
+     * </p>
+     *
+     * <p>
+     *     If the position is expired, the processor can get the according 
latest
+     *     transaction ID in this map. And then the processor can clear all the
+     *     transaction IDs in the aborts {@link 
SnapshotSegmentAbortedTxnProcessorImpl#aborts}
+     *     that lower than the transaction ID.
+     *     And then the processor can delete the segments persistently 
according to
+     *     the positions.
+     * </p>
+     */
+    private final LinkedMap<PositionImpl, TxnID> segmentIndex = new 
LinkedMap<>();
+
+    /**
+     * This map is used to check whether a transaction is an aborted 
transaction.
+     * <p>
+     *     The transaction IDs is appended in order, so the processor can 
delete expired
+     *     transaction IDs according to the latest expired transaction IDs in 
segmentIndex
+     *     {@link SnapshotSegmentAbortedTxnProcessorImpl#segmentIndex}.
+     * </p>
+     */
+    private final LinkedMap<TxnID, TxnID> aborts = new LinkedMap<>();
+    /**
+     * This map stores the indexes of the snapshot segment.
+     * <p>
+     *     The key is the persistent position of the marker of the last 
transaction in the segment.
+     *     The value TransactionBufferSnapshotIndex {@link 
TransactionBufferSnapshotIndex} is the
+     *     indexes of the snapshot segment.
+     * </p>
+     */
+    private final LinkedMap<PositionImpl, TransactionBufferSnapshotIndex> 
indexes = new LinkedMap<>();
+
+    private final PersistentTopic topic;
+
+    private volatile long lastSnapshotTimestamps;
+
+    /**
+     * The number of the aborted transaction IDs in a segment.
+     * This is calculated according to the configured memory size.
+     */
+    private final int snapshotSegmentCapacity;
+    /**
+     * Responsible for executing the persistent tasks.
+     * <p>Including:</p>
+     * <p>    Update segment index.</p>
+     * <p>    Write snapshot segment.</p>
+     * <p>    Delete snapshot segment.</p>
+     * <p>    Clear all snapshot segment. </p>
+     */
+    private final PersistentWorker persistentWorker;
+
+    private static final String SNAPSHOT_PREFIX = "multiple-";
+
+    public SnapshotSegmentAbortedTxnProcessorImpl(PersistentTopic topic) {
+        this.topic = topic;
+        this.persistentWorker = new PersistentWorker(topic);
+        /*
+           Calculate the segment capital according to its size configuration.
+           <p>
+               The empty transaction segment size is 5.
+               Adding an empty linkedList, the size increase to 6.
+               Add the topic name the size increase to the 7 + 
topic.getName().length().
+               Add the aborted transaction IDs, the size increase to 8 +
+               topic.getName().length() + 3 * aborted transaction ID size.
+           </p>
+         */
+        this.snapshotSegmentCapacity = (topic.getBrokerService().getPulsar()
+                .getConfiguration().getTransactionBufferSnapshotSegmentSize() 
- 8 - topic.getName().length()) / 3;
+        this.unsealedTxnIds = new LinkedList<>();
+    }
+
+    @Override
+    public void putAbortedTxnAndPosition(TxnID txnID, PositionImpl position) {
+        unsealedTxnIds.add(txnID);
+        aborts.put(txnID, txnID);
+        /*
+           The size of lastAbortedTxns reaches the configuration of the size 
of snapshot segment.
+           Append a task to persistent the segment with the aborted 
transaction IDs and the latest
+           transaction mark persistent position passed by param.
+         */
+        if (unsealedTxnIds.size() >= snapshotSegmentCapacity) {
+            LinkedList<TxnID> abortedSegment = unsealedTxnIds;
+            segmentIndex.put(position, txnID);
+            
persistentWorker.appendTask(PersistentWorker.OperationType.WriteSegment,
+                    () -> 
persistentWorker.takeSnapshotSegmentAsync(abortedSegment, position));
+            this.unsealedTxnIds = new LinkedList<>();
+        }
+    }
+
+    @Override
+    public boolean checkAbortedTransaction(TxnID txnID) {
+        return aborts.containsKey(txnID);
+    }
+
+    /**
+     * Check werther the position in segmentIndex {@link 
SnapshotSegmentAbortedTxnProcessorImpl#segmentIndex}
+     * is expired. If the position is not exist in the original topic, the 
according transaction is an invalid
+     * transaction. And the according segment is invalid, too. The transaction 
IDs before the transaction ID
+     * in the aborts are invalid, too.
+     */
+    @Override
+    public void trimExpiredAbortedTxns() {
+        //Checking whether there are some segment expired.
+        List<PositionImpl> positionsNeedToDelete = new ArrayList<>();
+        while (!segmentIndex.isEmpty() && !((ManagedLedgerImpl) 
topic.getManagedLedger())
+                .ledgerExists(segmentIndex.firstKey().getLedgerId())) {
+            if (log.isDebugEnabled()) {
+                log.debug("[{}] Topic transaction buffer clear aborted 
transactions, maxReadPosition : {}",
+                        topic.getName(), segmentIndex.firstKey());
+            }
+            PositionImpl positionNeedToDelete = segmentIndex.firstKey();
+            positionsNeedToDelete.add(positionNeedToDelete);
+
+            TxnID theLatestDeletedTxnID = segmentIndex.remove(0);
+            while (!aborts.firstKey().equals(theLatestDeletedTxnID)) {
+                aborts.remove(0);
+            }
+            aborts.remove(0);
+        }
+        //Batch delete the expired segment
+        if (!positionsNeedToDelete.isEmpty()) {
+            
persistentWorker.appendTask(PersistentWorker.OperationType.DeleteSegment,
+                    () -> 
persistentWorker.deleteSnapshotSegment(positionsNeedToDelete));
+        }
+    }
+
+    private String buildKey(long sequenceId) {
+        return SNAPSHOT_PREFIX + sequenceId + "-" + this.topic.getName();
+    }
+
+    @Override
+    public CompletableFuture<Void> takeAbortedTxnsSnapshot(PositionImpl 
maxReadPosition) {
+        //Store the latest aborted transaction IDs in unsealedTxnIDs and the 
according the latest max read position.
+        TransactionBufferSnapshotIndexesMetadata metadata = new 
TransactionBufferSnapshotIndexesMetadata(
+                maxReadPosition.getLedgerId(), maxReadPosition.getEntryId(),
+                convertTypeToTxnIDData(unsealedTxnIds));
+        return 
persistentWorker.appendTask(PersistentWorker.OperationType.UpdateIndex,
+                () -> persistentWorker.updateSnapshotIndex(metadata, 
indexes.values().stream().toList()));
+    }
+
+    @Override
+    public CompletableFuture<PositionImpl> recoverFromSnapshot() {
+        return 
topic.getBrokerService().getPulsar().getTransactionBufferSnapshotServiceFactory()
+                .getTxnBufferSnapshotIndexService()
+                
.createReader(TopicName.get(topic.getName())).thenComposeAsync(reader -> {
+                    PositionImpl startReadCursorPosition = null;
+                    TransactionBufferSnapshotIndexes persistentSnapshotIndexes 
= null;
+                    try {
+                        /*
+                          Read the transaction snapshot segment index.
+                          <p>
+                              The processor can get the sequence ID, unsealed 
transaction IDs,
+                              segment index list and max read position in the 
snapshot segment index.
+                              Then we can traverse the index list to read all 
aborted transaction IDs
+                              in segments to aborts.
+                          </p>
+                         */
+                        while (reader.hasMoreEvents()) {
+                            Message<TransactionBufferSnapshotIndexes> message 
= reader.readNextAsync()
+                                    .get(getSystemClientOperationTimeoutMs(), 
TimeUnit.MILLISECONDS);
+                            if (topic.getName().equals(message.getKey())) {
+                                TransactionBufferSnapshotIndexes 
transactionBufferSnapshotIndexes = message.getValue();
+                                if (transactionBufferSnapshotIndexes != null) {
+                                    persistentSnapshotIndexes = 
transactionBufferSnapshotIndexes;
+                                    startReadCursorPosition = PositionImpl.get(
+                                            
transactionBufferSnapshotIndexes.getSnapshot().getMaxReadPositionLedgerId(),
+                                            
transactionBufferSnapshotIndexes.getSnapshot().getMaxReadPositionEntryId());
+                                }
+                            }
+                        }
+                    } catch (TimeoutException ex) {
+                        Throwable t = FutureUtil.unwrapCompletionException(ex);
+                        String errorMessage = String.format("[%s] Transaction 
buffer recover fail by read "
+                                + "transactionBufferSnapshot timeout!", 
topic.getName());
+                        log.error(errorMessage, t);
+                        return FutureUtil.failedFuture(
+                                new 
BrokerServiceException.ServiceUnitNotReadyException(errorMessage, t));
+                    } catch (Exception ex) {
+                        log.error("[{}] Transaction buffer recover fail when 
read "
+                                + "transactionBufferSnapshot!", 
topic.getName(), ex);
+                        return FutureUtil.failedFuture(ex);
+                    } finally {
+                        closeReader(reader);
+                    }
+                    PositionImpl finalStartReadCursorPosition = 
startReadCursorPosition;
+                    TransactionBufferSnapshotIndexes 
finalPersistentSnapshotIndexes = persistentSnapshotIndexes;
+                    if (persistentSnapshotIndexes == null) {
+                        return CompletableFuture.completedFuture(null);
+                    } else {
+                        this.unsealedTxnIds = 
convertTypeToTxnID(persistentSnapshotIndexes
+                                .getSnapshot().getAborts());
+                    }
+                    //Read snapshot segment to recover aborts.
+                    ArrayList<CompletableFuture<Void>> completableFutures = 
new ArrayList<>();
+                    CompletableFuture<Void> 
openManagedLedgerAndHandleSegmentsFuture = new CompletableFuture<>();
+                    AtomicBoolean hasInvalidIndex = new AtomicBoolean(false);
+                    AsyncCallbacks.OpenReadOnlyManagedLedgerCallback callback 
= new AsyncCallbacks
+                            .OpenReadOnlyManagedLedgerCallback() {
+                        @Override
+                        public void 
openReadOnlyManagedLedgerComplete(ReadOnlyManagedLedgerImpl 
readOnlyManagedLedger,
+                                                                      Object 
ctx) {
+                            
finalPersistentSnapshotIndexes.getIndexList().forEach(index -> {
+                                CompletableFuture<Void> handleSegmentFuture = 
new CompletableFuture<>();
+                                completableFutures.add(handleSegmentFuture);
+                                readOnlyManagedLedger.asyncReadEntry(
+                                        new 
PositionImpl(index.getSegmentLedgerID(),
+                                                index.getSegmentEntryID()),
+                                        new AsyncCallbacks.ReadEntryCallback() 
{
+                                            @Override
+                                            public void 
readEntryComplete(Entry entry, Object ctx) {
+                                                
handleSnapshotSegmentEntry(entry);
+                                                indexes.put(new PositionImpl(
+                                                                
index.abortedMarkLedgerID,
+                                                                
index.abortedMarkEntryID),
+                                                        index);
+                                                entry.release();
+                                                
handleSegmentFuture.complete(null);
+                                            }
+
+                                            @Override
+                                            public void 
readEntryFailed(ManagedLedgerException exception, Object ctx) {
+                                                /*
+                                                  The logic flow of deleting 
expired segment is:
+                                                  <p>
+                                                      1. delete segment
+                                                      2. update segment index
+                                                  </p>
+                                                  If the worker delete segment 
successfully
+                                                  but failed to update segment 
index,
+                                                  the segment can not be read 
according to the index.
+                                                  We update index again if 
there are invalid indexes.
+                                                 */
+                                                if (((ManagedLedgerImpl) 
topic.getManagedLedger())
+                                                        
.ledgerExists(index.getAbortedMarkLedgerID())) {
+                                                    log.error("[{}] Failed to 
read snapshot segment [{}:{}]",
+                                                            topic.getName(), 
index.segmentLedgerID,
+                                                            
index.segmentEntryID, exception);
+                                                    
handleSegmentFuture.completeExceptionally(exception);
+                                                } else {
+                                                    hasInvalidIndex.set(true);
+                                                }
+                                            }
+                                        }, null);
+                            });
+                            
openManagedLedgerAndHandleSegmentsFuture.complete(null);
+                        }
+
+                        @Override
+                        public void 
openReadOnlyManagedLedgerFailed(ManagedLedgerException exception, Object ctx) {
+                            log.error("[{}] Failed to open readOnly managed 
ledger", topic, exception);
+                            
openManagedLedgerAndHandleSegmentsFuture.completeExceptionally(exception);
+                        }
+                    };
+
+                    TopicName snapshotSegmentTopicName = 
TopicName.get(TopicDomain.persistent.toString(),
+                            
TopicName.get(topic.getName()).getNamespaceObject(),
+                            
SystemTopicNames.TRANSACTION_BUFFER_SNAPSHOT_SEGMENTS);
+                    
this.topic.getBrokerService().getPulsar().getManagedLedgerFactory()
+                            
.asyncOpenReadOnlyManagedLedger(snapshotSegmentTopicName
+                                            .getPersistenceNamingEncoding(), 
callback,
+                                    topic.getManagedLedger().getConfig(),
+                                    null);
+                    /*
+                       Wait the processor recover completely and then allow TB
+                       to recover the messages after the 
startReadCursorPosition.
+                     */
+                    return openManagedLedgerAndHandleSegmentsFuture
+                            .thenCompose((ignore) -> 
FutureUtil.waitForAll(completableFutures))
+                            .thenCompose((i) -> {
+                                /*
+                                  Update the snapshot segment index if there 
exist invalid indexes.
+                                 */
+                                if (hasInvalidIndex.get()) {
+                                    
persistentWorker.appendTask(PersistentWorker.OperationType.UpdateIndex, ()
+                                            -> persistentWorker
+                                            
.updateSnapshotIndex(finalPersistentSnapshotIndexes.getSnapshot(),
+                                            
indexes.values().stream().toList()));
+                                }
+                                /*
+                                   If there is no segment index, the 
persistent worker will write segment begin from 0.
+                                 */
+                                if (indexes.size() != 0) {
+                                    
persistentWorker.sequenceID.set(indexes.get(indexes.lastKey()).sequenceID + 1);
+                                }
+                                /*
+                                  Append the aborted txn IDs in the index 
metadata
+                                  can keep the order of the aborted txn in the 
aborts.
+                                  So that we can trim the expired snapshot 
segment in aborts
+                                  according to the latest transaction IDs in 
the segmentIndex.
+                                 */
+                                
convertTypeToTxnID(finalPersistentSnapshotIndexes.getSnapshot().getAborts())
+                                        .forEach(txnID -> aborts.put(txnID, 
txnID));
+                                return 
CompletableFuture.completedFuture(finalStartReadCursorPosition);
+                            }).exceptionally(ex -> {
+                                log.error("[{}] Failed to recover snapshot 
segment", this.topic.getName(), ex);
+                                return null;
+                            });
+
+                    },  
topic.getBrokerService().getPulsar().getTransactionExecutorProvider()
+                        .getExecutor(this));
+    }
+
+    @Override
+    public CompletableFuture<Void> clearAbortedTxnSnapshot() {
+        return 
persistentWorker.appendTask(PersistentWorker.OperationType.Clear,
+                persistentWorker::clearSnapshotSegmentAndIndexes);
+    }
+
+    @Override
+    public long getLastSnapshotTimestamps() {
+        return this.lastSnapshotTimestamps;
+    }
+
+    @Override
+    public CompletableFuture<Void> closeAsync() {
+        return persistentWorker.closeAsync();
+    }
+
+    private void handleSnapshotSegmentEntry(Entry entry) {
+        //decode snapshot from entry
+        ByteBuf headersAndPayload = entry.getDataBuffer();
+        //skip metadata
+        Commands.parseMessageMetadata(headersAndPayload);
+        TransactionBufferSnapshotSegment snapshotSegment = 
Schema.AVRO(TransactionBufferSnapshotSegment.class)
+                .decode(Unpooled.wrappedBuffer(headersAndPayload).nioBuffer());
+
+        TxnIDData lastTxn = 
snapshotSegment.getAborts().get(snapshotSegment.getAborts().size() - 1);
+        segmentIndex.put(new 
PositionImpl(snapshotSegment.getPersistentPositionLedgerId(),
+                snapshotSegment.getPersistentPositionEntryId()),
+                new TxnID(lastTxn.getMostSigBits(), 
lastTxn.getLeastSigBits()));
+        convertTypeToTxnID(snapshotSegment.getAborts()).forEach(txnID -> 
aborts.put(txnID, txnID));
+    }
+
+    private long getSystemClientOperationTimeoutMs() throws Exception {
+        PulsarClientImpl pulsarClient = (PulsarClientImpl) 
topic.getBrokerService().getPulsar().getClient();
+        return pulsarClient.getConfiguration().getOperationTimeoutMs();
+    }
+
+    private <T> void  closeReader(SystemTopicClient.Reader<T> reader) {
+        reader.closeAsync().exceptionally(e -> {
+            log.error("[{}]Transaction buffer snapshot reader close error!", 
topic.getName(), e);
+            return null;
+        });
+    }
+
+    /**
+     * The PersistentWorker be responsible for executing the persistent tasks, 
including:
+     * <p>
+     *     1. Write snapshot segment --- Encapsulate a sealed snapshot segment 
and persistent it.
+     *     2. Delete snapshot segment --- Evict expired snapshot segments.
+     *     3. Update snapshot indexes --- Update snapshot indexes after 
writing or deleting snapshot segment
+     *                                  or update snapshot indexes metadata 
regularly.
+     *     4. Clear all snapshot segments and indexes.  --- Executed when 
deleting this topic.
+     * </p>
+     * * Task 1 and task 2 will be put into a task queue. The tasks in the 
queue will be executed in order.
+     * * If the task queue is empty, task 3 will be executed immediately when 
it is appended to the worker.
+     * Else, the worker will try to execute the tasks in the task queue.
+     * * When task 4 was appended into worker, the worker will change the 
operation state to closed
+     * and cancel all tasks in the task queue. finally, execute the task 4 
(clear task).
+     * If there are race conditions, throw an Exception to let users try again.
+     */
+    public class PersistentWorker {
+        protected final AtomicLong sequenceID = new AtomicLong(0);
+
+        private final PersistentTopic topic;
+
+        //Persistent snapshot segment and index at the single thread.
+        private final 
CompletableFuture<SystemTopicClient.Writer<TransactionBufferSnapshotSegment>>
+                snapshotSegmentsWriterFuture;
+        private final 
CompletableFuture<SystemTopicClient.Writer<TransactionBufferSnapshotIndexes>>
+                snapshotIndexWriterFuture;
+
+        private enum OperationState {
+            None,
+            Operating,
+            Closed
+        }
+        private static final AtomicReferenceFieldUpdater<PersistentWorker, 
PersistentWorker.OperationState>
+                STATE_UPDATER = 
AtomicReferenceFieldUpdater.newUpdater(PersistentWorker.class,
+                PersistentWorker.OperationState.class, "operationState");
+
+        public enum OperationType {
+            UpdateIndex,
+            WriteSegment,
+            DeleteSegment,
+            Clear
+        }
+
+        private volatile OperationState operationState = OperationState.None;
+
+        ConcurrentLinkedDeque<Pair<OperationType, Pair<CompletableFuture<Void>,
+                Supplier<CompletableFuture<Void>>>>> taskQueue = new 
ConcurrentLinkedDeque<>();
+
+        public PersistentWorker(PersistentTopic topic) {
+            this.topic = topic;
+            this.snapshotSegmentsWriterFuture =  
this.topic.getBrokerService().getPulsar()
+                    .getTransactionBufferSnapshotServiceFactory()
+                    
.getTxnBufferSnapshotSegmentService().createWriter(TopicName.get(topic.getName()))
+                    .exceptionally(ex -> {
+                        log.error("{} Failed to create snapshot index writer", 
topic.getName());
+                        topic.close();
+                        return null;
+                    });
+            this.snapshotIndexWriterFuture =  
this.topic.getBrokerService().getPulsar()
+                    .getTransactionBufferSnapshotServiceFactory()
+                    
.getTxnBufferSnapshotIndexService().createWriter(TopicName.get(topic.getName()))
+                    .exceptionally((ex) -> {
+                        log.error("{} Failed to create snapshot writer", 
topic.getName());
+                        topic.close();
+                        return null;
+                    });
+        }
+
+        public CompletableFuture<Void> appendTask(OperationType operationType,
+                                                  
Supplier<CompletableFuture<Void>> task) {
+            CompletableFuture<Void> taskExecutedResult = new 
CompletableFuture<>();
+            switch (operationType) {
+                case UpdateIndex -> {
+                    /*
+                      The update index operation can be canceled when the task 
queue is not empty,
+                      so it should be executed immediately instead of 
appending to the task queue.
+                      If the taskQueue is not empty, the worker will execute 
the tasks in the queue.
+                     */
+                    if (!taskQueue.isEmpty()) {
+                        executeTask();
+                        return CompletableFuture.completedFuture(null);
+                    } else if (STATE_UPDATER.compareAndSet(this, 
OperationState.None, OperationState.Operating)) {
+                        return task.get().whenComplete((ignore, throwable) -> {
+                            if (throwable != null && log.isDebugEnabled()) {
+                                log.debug("[{}] Failed to update index 
snapshot", topic.getName(), throwable);
+                            }
+                            STATE_UPDATER.compareAndSet(this, 
OperationState.Operating, OperationState.None);
+                        });
+                    } else {
+                        return CompletableFuture.completedFuture(null);
+                    }
+                }
+                /*
+                  Only the operations of WriteSegment and DeleteSegment will 
be appended into the taskQueue.
+                  The operation will be canceled when the worker is close 
which means the topic is deleted.
+                 */
+                case WriteSegment, DeleteSegment -> {
+                    if 
(!STATE_UPDATER.get(this).equals(OperationState.Closed)) {
+                        taskQueue.add(new MutablePair<>(operationType, new 
MutablePair<>(taskExecutedResult, task)));
+                        executeTask();
+                        return taskExecutedResult;
+                    } else {
+                        return CompletableFuture.completedFuture(null);
+                    }
+                }
+                case Clear -> {
+                    /*
+                      Do not clear the snapshots if the topic is used.
+                      If the users want to delete a topic, they should stop 
the usage of the topic.
+                     */
+                    if (STATE_UPDATER.compareAndSet(this, OperationState.None, 
OperationState.Closed)) {
+                        taskQueue.forEach(pair ->
+                                
pair.getRight().getRight().get().completeExceptionally(
+                                        new 
BrokerServiceException.ServiceUnitNotReadyException(
+                                                String.format("Cancel the 
operation [%s] due to the"
+                                                                + " 
transaction buffer of the topic[%s] already closed",
+                                                        pair.getLeft().name(), 
this.topic.getName()))));
+                        taskQueue.clear();
+                        /*
+                          The task of clear all snapshot segments and indexes 
is executed immediately.
+                         */
+                        return task.get();
+                    } else {
+                        return FutureUtil.failedFuture(
+                                new BrokerServiceException.NotAllowedException(
+                                        String.format("Failed to clear the 
snapshot of topic [%s] due to "
+                                                + "the topic is used. Please 
stop the using of the topic "
+                                                + "and try it again", 
this.topic.getName())));
+                    }
+                }
+                default -> {
+                    return FutureUtil.failedFuture(new BrokerServiceException
+                            .NotAllowedException(String.format("Th operation 
[%s] is unsupported",
+                            operationType.name())));
+                }
+            }
+        }
+
+        private void executeTask() {
+            if (taskQueue.isEmpty()) {
+                return;
+            }
+            if (STATE_UPDATER.compareAndSet(this, OperationState.None, 
OperationState.Operating)) {
+                //Double-check. Avoid NoSuchElementException due to the first 
task is completed by other thread.
+                if (taskQueue.isEmpty()) {
+                    return;
+                }
+                Pair<OperationType, Pair<CompletableFuture<Void>, 
Supplier<CompletableFuture<Void>>>> firstTask =
+                        taskQueue.getFirst();
+                firstTask.getValue().getRight().get().whenComplete((ignore, 
throwable) -> {
+                    if (throwable != null) {
+                        if (log.isDebugEnabled()) {
+                            log.debug("[{}] Failed to do operation do 
operation of [{}]",
+                                    topic.getName(), 
firstTask.getKey().name(), throwable);
+                        }
+                        
firstTask.getRight().getKey().completeExceptionally(throwable);
+                    } else {
+                        firstTask.getRight().getKey().complete(null);
+                        taskQueue.removeFirst();
+                    }
+                    STATE_UPDATER.compareAndSet(this, OperationState.Operating,
+                            OperationState.None);
+                    //Execute the next task in the other thread.
+                    
topic.getBrokerService().getPulsar().getTransactionExecutorProvider()
+                            .getExecutor(this).submit(this::executeTask);
+                });
+            }
+        }
+
+        private CompletableFuture<Void> 
takeSnapshotSegmentAsync(LinkedList<TxnID> sealedAbortedTxnIdSegment,
+                                                                 PositionImpl 
abortedMarkerPersistentPosition) {
+            return writeSnapshotSegmentAsync(sealedAbortedTxnIdSegment, 
abortedMarkerPersistentPosition).thenRun(() -> {
+                if (log.isDebugEnabled()) {
+                    log.debug("Successes to take snapshot segment [{}] at 
maxReadPosition [{}] "
+                                    + "for the topic [{}], and the size of the 
segment is [{}]",
+                            this.sequenceID, abortedMarkerPersistentPosition, 
topic.getName(),
+                            sealedAbortedTxnIdSegment.size());
+                }
+                this.sequenceID.getAndIncrement();
+            }).exceptionally(e -> {
+                //Just log the error, and the processor will try to take 
snapshot again when the transactionBuffer
+                //append aborted txn next time.
+                log.error("Failed to take snapshot segment [{}] at 
maxReadPosition [{}] "
+                                + "for the topic [{}], and the size of the 
segment is [{}]",
+                        this.sequenceID, abortedMarkerPersistentPosition, 
topic.getName(),
+                        sealedAbortedTxnIdSegment.size(), e);
+                return null;
+            });
+        }
+
+        private CompletableFuture<Void> 
writeSnapshotSegmentAsync(LinkedList<TxnID> segment,
+                                                                  PositionImpl 
abortedMarkerPersistentPosition) {
+            TransactionBufferSnapshotSegment transactionBufferSnapshotSegment 
= new TransactionBufferSnapshotSegment();
+            
transactionBufferSnapshotSegment.setAborts(convertTypeToTxnIDData(segment));
+            
transactionBufferSnapshotSegment.setTopicName(this.topic.getName());
+            
transactionBufferSnapshotSegment.setPersistentPositionEntryId(abortedMarkerPersistentPosition.getEntryId());
+            transactionBufferSnapshotSegment.setPersistentPositionLedgerId(
+                    abortedMarkerPersistentPosition.getLedgerId());
+
+            return snapshotSegmentsWriterFuture.thenCompose(segmentWriter -> {
+                
transactionBufferSnapshotSegment.setSequenceId(this.sequenceID.get());
+                return 
segmentWriter.writeAsync(buildKey(this.sequenceID.get()), 
transactionBufferSnapshotSegment);
+            }).thenCompose((messageId) -> {
+                PositionImpl maxReadPosition = topic.getMaxReadPosition();
+                //Build index for this segment
+                TransactionBufferSnapshotIndex index = new 
TransactionBufferSnapshotIndex();
+                
index.setSequenceID(transactionBufferSnapshotSegment.getSequenceId());
+                
index.setAbortedMarkLedgerID(abortedMarkerPersistentPosition.getLedgerId());
+                
index.setAbortedMarkEntryID(abortedMarkerPersistentPosition.getEntryId());
+                index.setSegmentLedgerID(((MessageIdImpl) 
messageId).getLedgerId());
+                index.setSegmentEntryID(((MessageIdImpl) 
messageId).getEntryId());
+
+                indexes.put(abortedMarkerPersistentPosition, index);
+                //update snapshot segment index.
+                //If the index can not be written successfully, the snapshot 
segment wil be overwritten
+                // when the processor writes snapshot segment next time.
+                return updateSnapshotIndex(new 
TransactionBufferSnapshotIndexesMetadata(
+                                maxReadPosition.getLedgerId(), 
maxReadPosition.getEntryId(), new LinkedList<>()),
+                        indexes.values().stream().toList());
+            });
+        }
+
+        // update index after delete all segment.
+        private CompletableFuture<Void> 
deleteSnapshotSegment(List<PositionImpl> positionNeedToDeletes) {
+            List<CompletableFuture<Void>> results = new ArrayList<>();
+            for (PositionImpl positionNeedToDelete : positionNeedToDeletes) {
+                long sequenceIdNeedToDelete = 
indexes.get(positionNeedToDelete).getSequenceID();
+                results.add(snapshotSegmentsWriterFuture
+                        .thenCompose(writer -> 
writer.deleteAsync(buildKey(sequenceIdNeedToDelete), null))
+                        .thenRun(() -> {
+                            if (log.isDebugEnabled()) {
+                                log.debug("[{}] Successes to delete the 
snapshot segment, "
+                                                + "whose sequenceId is [{}] 
and maxReadPosition is [{}]",
+                                        this.topic.getName(), this.sequenceID, 
positionNeedToDelete);
+                            }
+                            //The process will check whether the snapshot 
segment is null,
+                            // and update index when recovered.
+                            indexes.remove(positionNeedToDelete);
+                        }).exceptionally(e -> {
+                            log.warn("[{}] Failed to delete the snapshot 
segment, "
+                                            + "whose sequenceId is [{}] and 
maxReadPosition is [{}]",
+                                    this.topic.getName(), this.sequenceID, 
positionNeedToDelete, e);
+                            return null;
+                        }));
+            }
+            return FutureUtil.waitForAll(results);
+        }
+
+        private CompletableFuture<Void> 
updateSnapshotIndex(TransactionBufferSnapshotIndexesMetadata snapshotSegment,
+                                                            
List<TransactionBufferSnapshotIndex> indexList) {
+            TransactionBufferSnapshotIndexes snapshotIndexes = new 
TransactionBufferSnapshotIndexes();

Review Comment:
   Yeap, fixed.



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