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InfluxDB
Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
And if you don't want to write it yourself, you use a library. I was always quite happy with Expresso, but as it is not JUST a parser for math expressions, you might need to look into security of executing unknown user input.
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