I have vernemq server and mqtt clients using paho mqtt library (with python or C - no matter). Both subscribers and publishers use Qos2 and clean_session == False. So the problem is when subscriber is offline, I try to send some messages. Some of them are lost. After a detailed study of the parameters, I found out that the first max_inflight_messages are lost. What I mean. In the config file vernemq.conf I set max_inflight_messages = 20 (by default). Then subscriber go to offline, I send 21 messages, then subscriber go online, and first 20 are lost, 21s is delivered. I tried it many times with different amount of messages - the same result, first 20 messages are lost, from 21 and next are received. When I try max_inflight_messages = 1, first message is lost, others are received. Any ideas? My file vernemq.conf:
allow_anonymous = on
allow_register_during_netsplit = off
allow_publish_during_netsplit = off
allow_subscribe_during_netsplit = off
allow_unsubscribe_during_netsplit = off
allow_multiple_sessions = off
coordinate_registrations = on
max_inflight_messages = 20
max_online_messages = 1000
max_offline_messages = 1000
max_message_size = 0
upgrade_outgoing_qos = off
listener.max_connections = 10000
listener.nr_of_acceptors = 10
listener.tcp.default = 0.0.0.0:1883
listener.vmq.clustering = 0.0.0.0:44053
listener.http.default = 0.0.0.0:8888
systree_enabled = on
systree_interval = 20000
graphite_enabled = off
graphite_host = localhost
graphite_port = 2003
graphite_interval = 20000
shared_subscription_policy = prefer_local
plugins.vmq_passwd = off
plugins.vmq_acl = on
plugins.vmq_diversity = off
plugins.vmq_webhooks = off
plugins.vmq_bridge = off
metadata_plugin = vmq_plumtree
vmq_acl.acl_file = ./etc/vmq.acl
vmq_acl.acl_reload_interval = 10
vmq_passwd.password_file = ./etc/vmq.passwd
vmq_passwd.password_reload_interval = 10
vmq_diversity.script_dir = ./share/lua
vmq_diversity.auth_postgres.enabled = off
vmq_diversity.postgres.ssl = off
vmq_diversity.postgres.password_hash_method = crypt
vmq_diversity.auth_cockroachdb.enabled = off
vmq_diversity.cockroachdb.ssl = on
vmq_diversity.cockroachdb.password_hash_method = bcrypt
vmq_diversity.auth_mysql.enabled = off
vmq_diversity.mysql.password_hash_method = password
vmq_diversity.auth_mongodb.enabled = off
vmq_diversity.mongodb.ssl = off
vmq_diversity.auth_redis.enabled = off
vmq_bcrypt.pool_size = 1
log.console = both
log.console.level = debug
log.console.file = ./log/console.log
log.error.file = ./log/error.log
log.syslog = off
log.crash = on
log.crash.file = ./log/crash.log
log.crash.maximum_message_size = 64KB
log.crash.size = 10MB
log.crash.rotation = $D0
log.crash.rotation.keep = 5
nodename = VerneMQ@127.0.0.1
distributed_cookie = vmq
erlang.async_threads = 64
erlang.max_ports = 262144
leveldb.maximum_memory.percent = 70
