# Cassandra 消息存储

提示

EMQX 3.1 版本后推出强大的规则引擎用于替换插件,建议您前往使用保存数据到 Cassandra规则引擎中创建 保存数据到 Cassandra

# 配置 Cassandra 服务器

配置文件: emqx_backend_cassa.conf

支持配置多台Cassandra服务器连接池:

## Cassandra 节点地址
backend.ecql.pool1.nodes = 127.0.0.1:9042

## Cassandra 连接池大小
backend.ecql.pool1.size = 8

## Cassandra 自动重连间隔(s)
backend.ecql.pool1.auto_reconnect = 1

## Cassandra 认证用户名/密码
backend.ecql.pool1.username = cassandra
backend.ecql.pool1.password = cassandra

## Cassandra Keyspace
backend.ecql.pool1.keyspace = mqtt

## Cassandra Logger type
backend.ecql.pool1.logger = info

##--------------------------------------------------------------------
## Cassandra Backend Hooks
##--------------------------------------------------------------------

## Client Connected Record
backend.cassa.hook.client.connected.1    = {"action": {"function": "on_client_connected"}, "pool": "pool1"}

## Subscribe Lookup Record
backend.cassa.hook.session.created.1     = {"action": {"function": "on_subscription_lookup"}, "pool": "pool1"}

## Client DisConnected Record
backend.cassa.hook.client.disconnected.1 = {"action": {"function": "on_client_disconnected"}, "pool": "pool1"}

## Lookup Unread Message QOS > 0
backend.cassa.hook.session.subscribed.1  = {"topic": "#", "action": {"function": "on_message_fetch"}, "pool": "pool1"}

## Lookup Retain Message
backend.cassa.hook.session.subscribed.2  = {"action": {"function": "on_retain_lookup"}, "pool": "pool1"}

## Store Publish Message  QOS > 0
backend.cassa.hook.message.publish.1     = {"topic": "#", "action": {"function": "on_message_publish"}, "pool": "pool1"}

## Delete Acked Record
backend.cassa.hook.session.unsubscribed.1= {"topic": "#", action": {"cql": ["delete from acked where client_id = ${clientid} and topic = ${topic}"]}, "pool": "pool1"}

## Store Retain Message
backend.cassa.hook.message.publish.2     = {"topic": "#", "action": {"function": "on_message_retain"}, "pool": "pool1"}

## Delete Retain Message
backend.cassa.hook.message.publish.3     = {"topic": "#", "action": {"function": "on_retain_delete"}, "pool": "pool1"}

## Store Ack
backend.cassa.hook.message.acked.1       = {"topic": "#", "action": {"function": "on_message_acked"}, "pool": "pool1"}

## 获取离线消息
### "offline_opts": 获取离线消息的配置
####   - max_returned_count: 单次拉去的最大离线消息数目
####   - time_range: 仅拉去在当前时间范围的消息
## backend.cassa.hook.session.subscribed.1  = {"topic": "#", "action": {"function": "on_message_fetch"}, "offline_opts": {"max_returned_count": 500, "time_range": "2h"}, "pool": "pool1"}

## 如果需要存储 Qos0 消息, 可开启以下配置
## 警告: 当开启以下配置时, 需关闭 'on_message_fetch', 否则 qos1, qos2 消息会被存储俩次
## backend.cassa.hook.message.publish.4     = {"topic": "#", "action": {"function": "on_message_store"}, "pool": "pool1"}
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backend 消息存储规则包括:

hooktopicaction说明
client.connectedon_client_connected存储客户端在线状态
session.createdon_subscribe_lookup订阅主题
client.disconnectedon_client_disconnected存储客户端离线状态
session.subscribed#on_message_fetch获取离线消息
session.subscribed#on_retain_lookup获取retain消息
session.unsubscribed#删除 akced 消息
message.publish#on_message_publish存储发布消息
message.publish#on_message_retain存储retain消息
message.publish#on_retain_delete删除retain消息
message.acked#on_message_acked消息ACK处理

自定义 CQL 语句 可用参数包括:

hook可用参数示例(cql语句中${name} 表示可获取的参数)
client.connectedclientidinsert into conn(clientid) values(${clientid})
client.disconnectedclientidinsert into disconn(clientid) values(${clientid})
session.subscribedclientid, topic, qosinsert into sub(topic, qos) values(${topic}, ${qos})
session.unsubscribedclientid, topicdelete from sub where topic = ${topic}
message.publishmsgid, topic, payload, qos, clientidinsert into msg(msgid, topic) values(${msgid}, ${topic})
message.ackedmsgid, topic, clientidinsert into ack(msgid, topic) values(${msgid}, ${topic})
message.delivermsgid, topic, clientidinsert into deliver(msgid, topic) values(${msgid}, ${topic})

支持 CQL 语句配置:

考虑到用户的需求不同, backend cassandra 自带的函数无法满足用户需求, 用户可根据自己的需求配置 cql 语句

在 etc/plugins/emqx_backend_cassa.conf 中添加如下配置:

## 在客户端连接到 EMQX 服务器后,执行一条 cql 语句(支持多条 cql 语句)
backend.cassa.hook.client.connected.3 = {"action": {"cql": ["insert into conn(clientid) values(${clientid})"]}, "pool": "pool1"}
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# Cassandra 创建一个 Keyspace

CREATE KEYSPACE mqtt WITH replication = {'class': 'SimpleStrategy', 'replication_factor': '1'}  AND durable_writes = true;
USR mqtt;
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# 导入 Cassandra 表结构

cqlsh -e "SOURCE 'emqx_backend_cassa.cql'"
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# Cassandra 用户状态表(Client Table)

mqtt.client 存储设备在线状态:

CREATE TABLE mqtt.client (
  client_id text PRIMARY KEY,
  connected timestamp,
  disconnected timestamp,
  node text,
  state int
);
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查询设备在线状态:

select * from mqtt.client where client_id = ${clientid};
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例如 ClientId 为 test 的客户端上线:

select * from mqtt.client where client_id = 'test';

 client_id | connected                       | disconnected  | node            | state
-----------+---------------------------------+---------------+-----------------+-------
      test | 2017-02-14 08:27:29.872000+0000 |          null | emqx@127.0.0.1|   1
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例如ClientId为test客户端下线:

select * from mqtt.client where client_id = 'test';

 client_id | connected                       | disconnected                    | node            | state
-----------+---------------------------------+---------------------------------+-----------------+-------
      test | 2017-02-14 08:27:29.872000+0000 | 2017-02-14 08:27:35.872000+0000 | emqx@127.0.0.1|     0
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# Cassandra 用户订阅主题表(Sub Table)

mqtt.sub 存储订阅关系:

CREATE TABLE mqtt.sub (
  client_id text,
  topic text,
  qos int,
  PRIMARY KEY (client_id, topic)
);
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用户test分别订阅主题test_topic1 test_topic2:

insert into mqtt.sub(client_id, topic, qos) values('test', 'test_topic1', 1);
insert into mqtt.sub(client_id, topic, qos) values('test', 'test_topic2', 2);
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某个客户端订阅主题:

select * from mqtt_sub where clientid = ${clientid};
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查询ClientId为'test'的客户端已订阅主题:

select * from mqtt_sub where clientid = 'test';

 client_id | topic       | qos
-----------+-------------+------
      test | test_topic1 |   1
      test | test_topic2 |   2
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# Cassandra 发布消息表(Msg Table)

mqtt.msg 存储MQTT消息:

CREATE TABLE 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);
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查询某个客户端发布的消息:

select * from mqtt_msg where sender = ${clientid};
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查询ClientId为'test'的客户端发布的消息:

select * from mqtt_msg where sender = 'test';

 topic | msgid                | arrived                         | payload      | qos | retain | sender
-------+----------------------+---------------------------------+--------------+-----+--------+--------
 hello | 2PguFrHsrzEvIIBdctmb | 2017-02-14 09:07:13.785000+0000 | Hello world! |   1 |      0 |   test
 world | 2PguFrHsrzEvIIBdctmb | 2017-02-14 09:07:13.785000+0000 | Hello world! |   1 |      0 |   test
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# Cassandra 保留消息表(Retain Message Table)

mqtt.retain 存储 Retain 消息:

CREATE TABLE mqtt.retain (
  topic text PRIMARY KEY,
  msgid text
);
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查询 retain 消息:

select * from mqtt_retain where topic = ${topic};
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查询 topic 为 't/retain' 的 retain 消息:

select * from mqtt_retain where topic = 't/retain';

 topic  | msgid
--------+----------------------
 retain | 2PguFrHsrzEvIIBdctmb
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# Cassandra 接收消息 ack 表(Message Acked Table)

mqtt.acked 存储客户端消息确认:

CREATE TABLE mqtt.acked (
  client_id text,
  topic text,
  msgid text,
  PRIMARY KEY (client_id, topic)
);
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# 启用 Cassandra 存储插件

./bin/emqx_ctl plugins load emqx_backend_cassa
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