This article discusses issues related to the databases for time series. Time series are widely used
in various applications. Accordingly, the theme of time series persistence is very important. The description
of time series persistence and processing from the perspective of the database is the subject
of this article. This paper deals with the use of traditional relational databases to store time series, as
well as solutions that are classified as NoSQL systems. Of course, under certain conditions, which are
discussed in this article, we can use traditional relational databases. Possible limitations are primarily
associated with the new data accumulation rate. In this connection, we discuss fractal trees as optimal
indexes for time series in relational databases. As the useful data processing tool, we describe
widow functions and other SQL extensions for time series processing. On the other hand, possible
limitations and peculiarities of processing time series lead to the need to use specialized systems for
storing time series. NoSQL solutions present a rich set of tools for time series processing. We discuss
data models (structured files, column-based databases) as well as data formats and network protocols
for time series. As a general result of our survey, it can be concluded that the choice of solutions for
time series databases is determined, primarily, by the rate of arrival of new data. From NoSQL solutions,
Cassandra is the preferred choice.
Key words
time series, databases, NoSQL, Internet of Things.