What do self-driving cars, smart homes, autonomous stock/crypto trading algorithms, or energy sensor systems have in common? These applications are all based on a form of data that measures how things change over time. It’s called time-series data and it plays a very important role in our lives today.
Accordingly, time-series databases also became a hot topic.
What is a time-series database?
A time-series database (TSDB) can be defined simply as a database optimized for storing and using time-stamped or time-series data. You don’t need to use a TSDB to work with time-series data. Any relational or NoSQL database or a key-value-store will do, e.g. MongoDB or redis. However, when dealing with time-series data (e.g. temperature, air pressure or car velocity data), a TSDB makes your life as a developer a hell of a lot easier.
Indeed, the two main reasons why TSDBs is the fastest-growing category of databases, are usability and scalability. A purpose-built time-series database typically includes common functions of time-series data analysis, which is convenient when working with time-series data. Because time-series data typically continually produces new data entries, data grows pretty quickly, and with high-frequency data or many time-series data sources, data ingestion quickly becomes a challenge. Time-series databases are optimized to scale well for time-series data with time being a common denominator and outperform any other database without specific time-series optimizations. This is why more and more people are adopting time-series databases and using them for a variety of use cases.
What are time-series database use cases?
Monitoring sensor data
One of the use cases is the monitoring of sensor data for safety measurements, predictive maintenance, or assistance functions. E.g. a car stores and uses all kinds of sensor data like tyre pressure, surrounding temperature and humidity for driver assistance and maintenance support. An aircraft monitors gravity and aerodynamic principles to reassure pilots that everything is alright – or to alert them that something has gone wrong. In fact, a Boeing creates on average half a terabyte of data per flight, most of which is time-series data. 
Tracking assets is ideal for a time-series database as you constantly want to monitor where assets are, e.g. the cars of a fleet or any goods you might be stocking or shipping. These applications typically include unique vehicle or asset IDs, GPS coordinates, and additional metadata per timestamp. Apart from keeping track of the assets in realtime, you also can use the data for logistics and optimize e.g. your stocking and delivery processes.
Analyzing and predicting shopping behavior
Or, many e-commerce systems store all information of an item from product inventory, logistics data and any available environmental data to transaction amount, all items of the shopping cart purchased, to payment data, order information etc. In this case, a TSDB will be used to collect these large amounts of data and analyze them quickly to determine e.g. what to recommend to customers to buy next or optimize the inventory or predict future shopping behavior.
What are the most popular time series databases?
Well, here is our list of popular / established time series databases to use in 2020 to get you started:
- InfluxDB: an open-source time series database, written in Go and optimized for high-availability storage and retrieval of time series data for operations monitoring, application metrics, IoT sensor data, and real-time analytics
- KairosDB: a fast distributed scalable time series database written on top of Cassandra.
- Kdb+: is a column-based relational time series database with a focus on applications in the financial sector.
- Objectbox TS: superfast object persistence with time-series data on the edge. Collect, store, and query time-series data on the edge and sync selective data to / from a central location on-premise or in the cloud as needed.
- TimescaleDB: an open-source database designed to make SQL scalable for time-series data. It is engineered up from PostgreSQL and packaged as a PostgreSQL extension with full SQL support.
For an overview of time-series databases currently available for productive use, see DB Engines. The database of databases is also a good resource if you are deeply interested in the database landscape; it is more extensive, but it includes any DB available independent of the level of support or if it is still maintained, also hobby projects.
What do you do when you have more than just time-series data?
Typically, a time-series database is not well suited to model non-time-based data. Therefore, many companies choose to implement two databases. This increases overhead, disk space, and is especially impractical when you deal with edge devices.
Time Series + Object-Oriented Data Persistence
Storing and processing both time series data and objects, developers can collect complex datasets and combine them with time-series data. Combining these data types gives a more complete understanding and context to the data – not just what happens over time, but also other factors that affect the results.
The best option is a robust object-oriented database solution that lets you model your data as it reflects the factual use case / the real world in objects and on-top is optimized for time series data. You can model your world in objects and combine this with the power of time-series data to identify patterns in your data. If this is indeed a database optimized for restricted devices and Edge Computing, you can even use this data in real-time and on the device. By combining time series data with more complex data types, an object time-series edge database can empower new use cases on the edge based on a fast and easy all-in-one data persistence solution.
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 Time Series Management Systems: A Survey Søren Kejser Jensen, Torben Bach Pedersen, Senior Member, IEEE, Christian Thomsen