max.in.flight.requests.per.connection — Kafka Producer Configuration
The maximum number of unacknowledged requests the client will send on a single connection before blocking. Note that if this configuration is set to be greater than 1 and enable.
Description
The maximum number of unacknowledged requests the client will send on a single connection before blocking. Note that if this configuration is set to be greater than 1 and enable.idempotence is set to false, there is a risk of message reordering after a failed send due to retries (i.e., if retries are enabled); if retries are disabled or if enable.idempotence is set to true, ordering will be preserved. Additionally, enabling idempotence requires the value of this configuration to be less than or equal to 5. If conflicting configurations are set and idempotence is not explicitly enabled, idempotence is disabled.
Default Values by Kafka Version
| Kafka Version | Default Value |
|---|---|
| 0.9.0 | 5 |
| 0.10.0 | 5 |
| 0.10.1 | 5 |
| 0.10.2 | 5 |
| 0.11.0 | 5 |
| 1.0 | 5 |
| 1.1 | 5 |
| 2.0 | 5 |
| 2.1 | 5 |
| 2.2 | 5 |
| 2.3 | 5 |
| 2.4 | 5 |
| 2.5 | 5 |
| 2.6 | 5 |
| 2.7 | 5 |
| 2.8 | 5 |
| 3.0 | 5 |
| 3.1 | 5 |
| 3.2 | 5 |
| 3.3 | 5 |
| 3.4 | 5 |
| 3.5 | 5 |
| 3.6 | 5 |
| 3.7 | 5 |
| 3.8 | 5 |
| 3.9 | 5 |
| 4.0 | 5 |
| 4.1 | 5 |
| 4.2 | 5 |
Tuning Recommendation
| Profile | Recommended | Why |
|---|---|---|
| producer / throughput | 5 | The default of 5 is already the safe maximum with enable.idempotence=true (idempotence guarantees deduplication for up to 5 in-flight batches per partition); going higher would disable idempotence and risk reordering on retry. |
| producer / latency | 5 | Keep at 5 (default): pipelining 5 in-flight requests per broker connection saturates the TCP pipe without waiting for previous acks, minimizing head-of-line blocking and keeping request latency low even when brokers are slightly slow to respond. |
| producer / durability | 5 | The idempotent producer guarantees ordering and deduplication for up to 5 in-flight batches per partition; keeping the default of 5 preserves throughput while maintaining idempotence. Reducing to 1 is only needed if idempotence is disabled. |
Related Configs
acks · enable.idempotence · retries