关于influxdb:InfluxDB-Continuous-Query解析

Continuous Query(CQ)是外部周期运行的InfluxQL的查问，将查问后果写入指定的measurement，用它能够实现降采样downsampling。

联合CQ和RP(Retention Policy)，能够将历史数据保留为低精度，最近的数据保留为高精度，以升高存储用量。

Continuous Query的语法结构：

CREATE CONTINUOUS QUERY <cq_name> ON <database_name>
BEGIN
<cq_query>
END

其中的<cq_query>须要一个函数，一个INTO字句和一个GROUP BY time()字句，其语句构造：

SELECT <function[s]> INTO <destination_measurement> FROM <measurement> [WHERE <stuff>] GROUP BY time(<interval>)[,<tag_key[s]>]

举个简略的例子

将cpu.user数据进行5m均匀：

CREATE CONTINUOUS QUERY "cq_5" ON falcon 
BEGIN 
SELECT mean(value) INTO falcon.autogen."5_cpu.user" FROM falcon.autogen."cpu.user" GROUP BY time(5m), * 
END

其中的falcon.autogen.”5_cpu.user”，falcon示意database，autogen示意retention policy，5_cpu.user示意新的table。

//查问cq
> show continuous queries;
name: falcon
name  query
----  -----
cq_5  CREATE CONTINUOUS QUERY cq_5 ON falcon BEGIN SELECT mean(value) INTO falcon.autogen."5_cpu.user" FROM falcon.autogen."cpu.user" GROUP BY time(5m), * END

//查问cq中的数据
> select * from "5_cpu.user" order by time desc limit 10;
name: 5_cpu.user
time                 endpoint mean
----                 -------- ----
2020-06-09T04:55:00Z trovedev 6.806252400038498
2020-06-09T04:50:00Z trovedev 13.796289128479335
2020-06-09T04:45:00Z trovedev 16.57212610575366
2020-06-09T04:40:00Z trovedev 28.577591691423635
2020-06-09T04:35:00Z trovedev 6.02882334702075
2020-06-09T04:30:00Z trovedev 4.667398282326042
2020-06-09T04:25:00Z trovedev 4.746237171675345
2020-06-09T04:20:00Z trovedev 5.006169574660594
2020-06-09T04:15:00Z trovedev 5.002280037736261
2020-06-09T04:10:00Z trovedev 4.775274987155538

值得注意的是，CQ仅对实时的数据进行聚合，不会对历史数据聚合；也就是说，如果没有新的源数据，就不会产生新的聚合点。

逆向援用主动采样

应用通配符(*)和INTO查问的逆向援用语法，能够将db中的所有measurement依照对立的聚合办法进行采样，比方：将prometheus中的每个measuremnt每10min采样平均值，而后存入到opsultra的雷同名称的measurement中

create continuous query "cq_basic" on "prometheus" 
begin 
    select mean(*) into "opsultra"."six_month".:MEASUREMENT from /.*/ group by time(10m),* 
end

参考：
1.CQ:https://jasper-zhang1.gitbook…