离线消息保存到 Cassandra

搭建 Cassandra 数据库，并设置用户名密码为 root/public，以 MacOS X 为例:

$ brew install cassandra
## 修改配置，关闭匿名认证
$  vim /usr/local/etc/cassandra/cassandra.yaml
    authenticator: PasswordAuthenticator
    authorizer: CassandraAuthorizer
$ brew services start cassandra
## 创建 root 用户
$ cqlsh -ucassandra -pcassandra
create user root with password 'public' superuser;

初始化 Cassandra 表空间:

$ cqlsh -uroot -ppublic
CREATE KEYSPACE mqtt WITH replication = {'class': 'SimpleStrategy', 'replication_factor': '1'}  AND durable_writes = true;

创建 mqtt_msg 表:

CREATE TABLE mqtt.mqtt_msg (
    topic text,
    msgid text,
    arrived timestamp,
    payload text,
    qos int,
    retain int,
    sender text,
    PRIMARY KEY (topic, msgid)
) WITH CLUSTERING ORDER BY (msgid DESC)
    AND bloom_filter_fp_chance = 0.01
    AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
    AND comment = ''
    AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
    AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
    AND crc_check_chance = 1.0
    AND dclocal_read_repair_chance = 0.1
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND read_repair_chance = 0.0
    AND speculative_retry = '99PERCENTILE';
CREATE TABLE mqtt.acked (
    clientid text,
    topic text,
    msgid text,
    PRIMARY KEY (clientid, topic)
) WITH CLUSTERING ORDER BY (topic ASC)
    AND bloom_filter_fp_chance = 0.01
    AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
    AND comment = ''
    AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
    AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
    AND crc_check_chance = 1.0
    AND dclocal_read_repair_chance = 0.1
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND read_repair_chance = 0.0
    AND speculative_retry = '99PERCENTILE';

WARNING

消息表结构不能修改，请使用上面SQL语句创建

创建规则:

打开 EMQ X Dashboard (opens new window)，选择左侧的“规则”选项卡。

然后填写规则 SQL:

FROM说明

​ t/#: 发布者发布消息触发保存离线消息到Cassandra

​ $events/session_subscribed: 订阅者订阅主题触发获取离线消息

​ $events/message_acked: 订阅者回复消息ACK后触发删除已经被接收的离线消息

SELECT * FROM "t/#", "$events/session_subscribed", "$events/message_acked" WHERE topic =~ 't/#'

关联动作:

在“响应动作”界面选择“添加动作”，然后在“动作”下拉框里选择“离线消息保存到 Cassandra ”。

现在资源下拉框为空，可以点击右上角的 “新建” 来创建一个 Cassandra 资源:

弹出一个“创建资源”对话框

填写资源配置:

填写真实的 Cassandra 服务器地址，其他配置填写相应的值，然后点击 “测试连接” 按钮，确保连接测试成功。

最后点击 “确定” 按钮。

返回响应动作界面，点击 “确认”。

返回规则创建界面，点击 “创建”。

规则已经创建完成，通过 Dashboard 的 WebSocket 客户端发一条数据**(发布消息的QoS必须大于0)**:

消息发送后，通过 cqlsh 查看到消息被保存到 Cassandra 里面:

使用另外一个客户端，订阅主题 “t/1” (订阅主题的QoS必须大于0，否则消息会被重复接收):

订阅后马上接收到了保存到 Cassandra 里面的离线消息:

离线消息被接收后会在 Cassandra 中删除: