diff --git a/pulsar-broker/src/main/java/org/apache/pulsar/broker/transaction/buffer/impl/SnapshotSegmentAbortedTxnProcessorImpl.java b/pulsar-broker/src/main/java/org/apache/pulsar/broker/transaction/buffer/impl/SnapshotSegmentAbortedTxnProcessorImpl.java
index 385500dfbe9e7..69ba6c01d74d3 100644
--- a/pulsar-broker/src/main/java/org/apache/pulsar/broker/transaction/buffer/impl/SnapshotSegmentAbortedTxnProcessorImpl.java
+++ b/pulsar-broker/src/main/java/org/apache/pulsar/broker/transaction/buffer/impl/SnapshotSegmentAbortedTxnProcessorImpl.java
@@ -75,7 +75,7 @@ public class SnapshotSegmentAbortedTxnProcessorImpl implements AbortedTxnProcess
      * 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;
+    private volatile LinkedList<TxnID> unsealedTxnIds;
 
     /**
      * The map is used to clear the aborted transaction IDs persistent in the expired ledger.
@@ -372,7 +372,8 @@ public void openReadOnlyManagedLedgerFailed(ManagedLedgerException exception, Ob
                                    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);
+                                    PositionImpl lastKey = indexes.lastKey();
+                                    persistentWorker.sequenceID.set(indexes.get(lastKey).sequenceID + 1);
                                 }
                                 /*
                                   Append the aborted txn IDs in the index metadata
@@ -380,7 +381,9 @@ public void openReadOnlyManagedLedgerFailed(ManagedLedgerException exception, Ob
                                   So that we can trim the expired snapshot segment in aborts
                                   according to the latest transaction IDs in the segmentIndex.
                                  */
-                                unsealedTxnIds.forEach(txnID -> aborts.put(txnID, txnID));
+                                synchronized (unsealedTxnIds) {
+                                    unsealedTxnIds.forEach(txnID -> aborts.put(txnID, txnID));
+                                }
                                 return CompletableFuture.completedFuture(finalStartReadCursorPosition);
                             }).exceptionally(ex -> {
                                 log.error("[{}] Failed to recover snapshot segment", this.topic.getName(), ex);
@@ -462,7 +465,7 @@ public CompletableFuture<Void> clearAbortedTxnSnapshot() {
                 persistentWorker::clearSnapshotSegmentAndIndexes);
     }
 
-    public TransactionBufferStats generateSnapshotStats(boolean segmentStats) {
+    public synchronized TransactionBufferStats generateSnapshotStats(boolean segmentStats) {
         TransactionBufferStats transactionBufferStats = new TransactionBufferStats();
         transactionBufferStats.totalAbortedTransactions = this.aborts.size();
         transactionBufferStats.lastSnapshotTimestamps = this.lastSnapshotTimestamps;
@@ -496,7 +499,8 @@ private void handleSnapshotSegmentEntry(Entry entry) {
         TransactionBufferSnapshotSegment snapshotSegment = Schema.AVRO(TransactionBufferSnapshotSegment.class)
                 .decode(Unpooled.wrappedBuffer(headersAndPayload).nioBuffer());
 
-        TxnIDData lastTxn = snapshotSegment.getAborts().get(snapshotSegment.getAborts().size() - 1);
+        int size = snapshotSegment.getAborts().size();
+        TxnIDData lastTxn = snapshotSegment.getAborts().get(size - 1);
         segmentIndex.put(new PositionImpl(snapshotSegment.getPersistentPositionLedgerId(),
                 snapshotSegment.getPersistentPositionEntryId()),
                 new TxnID(lastTxn.getMostSigBits(), lastTxn.getLeastSigBits()));
@@ -719,7 +723,7 @@ private CompletableFuture<Void> takeSnapshotSegmentAsync(LinkedList<TxnID> seale
             return res;
         }
 
-        private CompletableFuture<Void> writeSnapshotSegmentAsync(LinkedList<TxnID> segment,
+        private synchronized CompletableFuture<Void> writeSnapshotSegmentAsync(LinkedList<TxnID> segment,
                                                                   PositionImpl abortedMarkerPersistentPosition) {
             TransactionBufferSnapshotSegment transactionBufferSnapshotSegment = new TransactionBufferSnapshotSegment();
             transactionBufferSnapshotSegment.setAborts(convertTypeToTxnIDData(segment));
@@ -881,4 +885,4 @@ private List<TxnIDData> convertTypeToTxnIDData(List<TxnID> abortedTxns) {
         return segment;
     }
 
-}
\ No newline at end of file
+}