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
client_redirect_check_interval_seconds	600	The client redirection check interval in seconds.
cluster_domain_resolve_timeout_seconds	120L	Timeout for resolving the cluster domain to discover seed nodes.
control_plane_burst_latency_ms	5000L	The max latency in milliseconds tolerated for the control plane burst.
data_plane_burst_latency_ms	5000L	The max latency in milliseconds tolerated for the data plane burst.
dist_server_dist_worker_call_queues	CPU cores	Number of dist worker call queues.
dist_worker_inline_fanout_threshold	1000	The threshold of the fanout to be executed in the calling thread.
dist_worker_fanout_parallelism	Max(2, CPU cores / 8)	Parallelism level for fanout operations.
dist_worker_cache_fanout_check_seconds	5	Interval seconds for checking cached routes against fanout related settings.
dist_worker_match_parallelism	Max(2, CPU cores / 2)	Parallelism level for match operations.
dist_worker_max_cached_subs_per_tenant	200_000L	Maximum cached subscriptions per tenant.
dist_worker_topic_match_expiry_seconds	60	Expiry time in seconds for topic matches.
inbox_check_queues_per_range	1	Number of check queues per range.
inbox_deliverers	100	Number of inbox deliverers.
inbox_fetch_queues_per_range	Max(1, CPU cores / 4)	Number of fetch queues per range.
inbox_meta_cache_expiry_second	300	Timeout in seconds before cached inbox metadata expires.
ingress_slowdown_direct_memory_usage	0.8	Threshold for slowing down ingress traffic based on direct memory usage.
ingress_slowdown_heap_memory_usage	0.9	Threshold for slowing down ingress traffic based on heap 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.
max_slowdown_timeout_seconds	5	Maximum duration (in seconds) that the slowdown mechanism is allowed to operate before further backpressure protection measures are taken.
mqtt_deliverers_per_server	CPU cores	Number of MQTT deliverers per server.
persistent_session_detach_timeout_second	7200	The timeout seconds to consider persistent session is probably detached from mqtt client.
session_register_num	10	Number of concurrent session registers.
maxActiveDedupChannels	1024	Maximum active deduplication channels per session.
maxActiveDedupTopicsPerChannel	10	Maximum active deduplication topics per channel.