前几条消息在传输到离线的mqtt客户端时丢失

Question

我有使用paho mqtt库的vernemq服务器和mqtt客户端(使用python或C-不要紧)。订阅服务器和发布服务器都使用Qos2和clean_session == False。所以问题是，当订阅者离线时，我会尝试发送一些消息。他们中的一些人迷路了。仔细研究参数后，我发现第一个max_inflight_messages丢失了。我的意思是。在配置文件vernemq.conf中，我设置了max_inflight_messages = 20 (默认情况下)。然后subscriber转到离线，我发送了21条消息，然后subscriber上线，前20条丢失，21条发送。我用不同数量的消息尝试了很多次-同样的结果，前20条消息丢失，21条消息和下一条消息被接收。当我尝试max_inflight_messages = 1时，第一条消息丢失，其他消息被接收。有什么想法吗？我的文件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

Answer 1

问题出在paho mqtt库中。当客户端连接到代理时，他会接收所有消息，但只有当消息被分配到具体主题时，才会分配此消息的处理程序。