Fix Pulsar Transaction Conflict Errors (2026)

A Pulsar transaction conflict error means a producer tried to commit a transaction that had already been committed or aborted by another producer.

Here’s how to diagnose and fix common causes:

1. Time Skew Between Brokers

Diagnosis: Check the system time on your Pulsar brokers. If they are significantly out of sync (more than a few seconds), it can lead to transaction ID conflicts.
```
ssh broker1 "date"
ssh broker2 "date"
# Compare output across all brokers
```
Fix: Synchronize the clocks on all Pulsar brokers using NTP.
```
# On each broker, ensure ntpdate or chrony is configured and running
sudo systemctl restart ntp # or chronyd
```
This ensures all brokers agree on the current time, preventing race conditions where a transaction appears committed or aborted by one broker while another still considers it active.

2. Producer ID Collision

Diagnosis: While rare, it’s possible for two distinct producers to be assigned the same producer ID if the transactionTimeout is set extremely high or if there are bugs in ID generation. Check broker logs for messages indicating producer ID reuse or conflicts.
Fix: Restarting Pulsar brokers can sometimes resolve transient ID issues if they are related to internal state. For a persistent fix, ensure your Pulsar version is up-to-date, as ID generation logic is continuously refined. If this persists, consider reducing transactionTimeout to force more frequent ID rotation.
```
# In broker.conf
transactionTimeout: 300000 # 5 minutes
```
A lower timeout forces producers to re-establish themselves more often, reducing the window for ID reuse.

3. Long-Running Transactions

Diagnosis: Transactions that remain open for an extended period can expire or be aborted by the broker due to inactivity or resource cleanup. Check broker logs for Transaction timed out or Transaction aborted due to inactivity messages.
Fix: Reduce the transactionTimeout setting in your Pulsar broker configuration.
```
# In broker.conf
transactionTimeout: 60000 # 1 minute
```
This forces transactions to be committed or aborted within a shorter timeframe, aligning with the expected producer behavior and preventing brokers from unilaterally cleaning them up.

4. Network Partitions or Broker Unavailability

Diagnosis: If a broker holding transaction state becomes unreachable for a period, other brokers might assume the transaction is abandoned and mark it as aborted. Check network connectivity between brokers and for any signs of broker restarts or failures in the cluster management logs (e.g., ZooKeeper or Kubernetes events).
Fix: Ensure robust network connectivity between brokers and ZooKeeper/Metadata Store. For stateful workloads, use a highly available metadata store. If brokers are restarting, investigate the root cause of the restarts (resource exhaustion, configuration errors, etc.). Pulsar’s transaction coordinator is designed to be resilient, but prolonged unavailability can lead to state divergence.

5. Incorrect Transaction Management by Producer

Diagnosis: The producer application might be incorrectly managing transaction lifecycles. This could involve attempting to commit a transaction after it has already been committed or aborted, or creating multiple transactions concurrently without proper coordination. Review the producer’s code logic for transaction handling.

Fix: Ensure that a transaction is committed or aborted exactly once. Implement retry logic carefully for commitTxn and abortTxn operations, but also include checks to prevent re-committing or re-aborting a transaction that has already reached a terminal state.

// Example in Java producer
try {
    producer.commitTxn(txnId);
    // Transaction committed successfully
} catch (PulsarAdminException.ConflictException e) {
    // Transaction already committed or aborted, this is often okay if idempotent
    log.warn("Transaction {} already committed/aborted", txnId, e);
} catch (Exception e) {
    // Handle other errors, potentially retry abortTxn
    producer.abortTxn(txnId);
}

This pattern ensures that if a commit fails due to a conflict, it’s logged and handled gracefully, rather than treating it as a new error.

6. ZooKeeper/Metadata Store Issues

Diagnosis: Pulsar uses ZooKeeper (or another metadata store like etcd) for transaction coordination. If ZooKeeper is experiencing high latency, network issues, or is overloaded, it can disrupt transaction state management, leading to conflicts. Check ZooKeeper logs and metrics for performance degradation.
```
# Example: Check ZooKeeper client connections and latency from a broker
echo stat | nc <zookeeper_host> 2181 | grep outstanding_requests
```
Fix: Ensure your ZooKeeper ensemble is properly sized, healthy, and has adequate network bandwidth. Optimize ZooKeeper configuration (e.g., tickTime, syncLimit) and consider dedicated network interfaces for ZooKeeper traffic. A stable and performant metadata store is critical for reliable transaction processing.

The next error you’ll likely encounter after fixing transaction conflicts is a ProducerFencedException if the producer was indeed the source of the problem and is now considered stale by the broker.