System Properties

Before adjusting system properties in BifroMQ, it's necessary to have a thorough understanding of its internal mechanisms, as inappropriate modifications can lead to unexpected behavior. Additionally, these system properties are closely linked with BifroMQ's internal implementation and may not be compatible across different versions. System properties can be set via JVM startup parameters, allowing for flexible customization of BifroMQ's behavior. For example, setting -Dmqtt_utf8_sanity_check=false disables the check for MQTT protocol-defined UTF8 string formats.

Below is a table listing the system properties supported by the current version:

Property Key	Default Value	Description
ingress_slowdown_direct_memory_usage	0.8	Threshold for slowing down ingress traffic based on direct memory usage.
mqtt_utf8_sanity_check	false	Enables/disables UTF8 sanity checks according to MQTT-1.5.3.
max_mqtt3_client_id_length	65535	Maximum client ID length for MQTT 3 clients.
max_mqtt5_client_id_length	65535	Maximum client ID length for MQTT 5 clients.
session_register_num	1000	Number of concurrent session registers.
data_plane_tolerable_latency_ms	1000L	Tolerable latency in milliseconds for the data plane.
data_plane_burst_latency_ms	5000L	Burst latency in milliseconds for the data plane.
control_plane_tolerable_latency_ms	2000L	Tolerable latency in milliseconds for the control plane.
control_plane_burst_latency_ms	5000L	Burst latency in milliseconds for the control plane.
dist_server_dist_worker_call_queues	CPU cores	Number of dist worker call queues.
dist_worker_fanout_parallelism	Max(2, CPU cores)	Parallelism level for fanout operations.
dist_worker_max_cached_subs_per_tenant	200_000L	Maximum cached subscriptions per tenant.
dist_worker_topic_match_expiry_seconds	5	Expiry time in seconds for topic matches.
dist_worker_match_parallelism	Max(2, CPU cores / 2)	Parallelism level for match operations.
dist_worker_fanout_split_threshold	100000	Threshold for splitting fanout operations when fanout split hinter enabled.
dist_worker_split_max_cpu_usage	0.8	Maximum CPU usage threshold for splitting operations when fanout split hinter enabled.
dist_worker_load_estimation_window_seconds	5L	Time window in seconds for load estimation when fanout split hinter enabled.
dist_worker_split_io_nanos_limit	30_000L	Nanoseconds limit for I/O operations during split when fanout split hinter enabled.
dist_worker_split_max_io_density	100	Maximum I/O density for split operations when fanout split hinter enabled.
dist_worker_range_voter_count	3	Number of voters for range decisions.
dist_worker_recovery_timeout_millis	10000L	Timeout in milliseconds for worker recovery when recovery balancer enabled.
inbox_deliverers	100	Number of inbox deliverers.
inbox_fetch_queues_per_range	Max(1, CPU cores / 4)	Number of fetch queues per range.
inbox_check_queues_per_range	1	Number of check queues per range.
inbox_store_load_estimation_window_seconds	5L	Time window in seconds for load estimation in inbox store.
inbox_store_range_split_max_cpu_usage	0.8	Maximum CPU usage threshold for range split in inbox store.
inbox_store_range_split_io_nanos_limit	30_000	Nanoseconds limit for I/O operations during range split in inbox store.
inbox_store_range_split_max_io_density	100	Maximum I/O density for range split operations in inbox store.
inbox_store_range_voter_count	1	Number of voters for range decisions in inbox store.
inbox_store_recovery_timeout_millis	10000L	Timeout in milliseconds for inbox store recovery.
mqtt_deliverers_per_server	CPU cores	Number of MQTT deliverers per server.
retain_store_range_split_max_cpu_usage	0.8	Maximum CPU usage threshold for range split in retain store.
retain_store_range_split_io_nanos_limit	30_000L	Nanoseconds limit for I/O operations during range split in retain store.
retain_store_range_split_max_io_density	100	Maximum I/O density for range split operations in retain store.
retain_store_range_voter_count	3	Number of voters for range decisions in retain store.
retain_store_load_est_window_seconds	5L	Time window in seconds for load estimation in retain store.
retain_store_recovery_timeout_millis	10000L	Timeout in milliseconds for retain store recovery.