其他时序数据库
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* RRDtool http://oss.oetiker.ch/rrdtool/
* 关联: `Graphite`  
* Kdb+  http://kx.com/
* Druid http://druid.io/
* KairosDB  http://kairosdb.github.io/


* from: https://www.sojson.com/blog/67.html
* RRD(round-robin-database): RRDtool使用的底层存储。C语言编写的。性能比较高
* whisper: Graphite底层的存储,Python写的
* prometheus: An open-source service monitoring system and time series database. 目前只有单机版本
* kairosdb: OpenTSDB的改善版，底层存储引擎是Cassandra。
* Heroic: Kairosdb的改善版，Spotify公司开源的时序数据库（Spotify的监控框架），引入了ElasticSearch作为元数据索引。目前还处于不稳定状态。

* CorfuDB: https://github.com/CorfuDB/CorfuDB::
  
    A cluster consistency platform


* TimescaleDB: https://www.timescale.com/::
  
    PostgreSQL for time‑series

* BTrDB: http://btrdb.io/::
  
    The Berkeley Tree DataBase provides very fast storage of 
      scalar-valued timeseries data

* Confluo: 
  * https://www.usenix.org/conference/nsdi19/presentation/khandelwal
  * https://github.com/ucbrise/confluo
  * Real-time Monitoring and Analysis of Data Streams