Data portability is certainly an important issue here to consider here given the points you mentioned. When adopting a vendor, the relevant question is "How much work is it to get data in?". And when planning for the contingency of vendor loss, the question is "How much work is it to get the data out?".
The first question is tied closely to the interfaces provided by the database, and those interfaces are usually commensurate with the associated tooling. In the case of time series databases, they include statsd, collectd, and good old JSON. Relational databases utilize SQL as expected. Take the example of migrating from Oracle to Postgres; you shouldn't have to spend an inordinate amount of retooling your applications because the data interfaces are similar.
Data egress is similar; SQL databases generally provide SQL/CSV exports, and most TSDBs (the good ones at least) allow you to get the data out via JSON through a REST interface.
Whether or not the DB you choose is open source, or from a small vendor, you should pick the right tool to solve your problem with data portability in mind. (disclosure, I work for http://irondb.io, and have used Postgres for 18 years)
The first question is tied closely to the interfaces provided by the database, and those interfaces are usually commensurate with the associated tooling. In the case of time series databases, they include statsd, collectd, and good old JSON. Relational databases utilize SQL as expected. Take the example of migrating from Oracle to Postgres; you shouldn't have to spend an inordinate amount of retooling your applications because the data interfaces are similar.
Data egress is similar; SQL databases generally provide SQL/CSV exports, and most TSDBs (the good ones at least) allow you to get the data out via JSON through a REST interface.
Whether or not the DB you choose is open source, or from a small vendor, you should pick the right tool to solve your problem with data portability in mind. (disclosure, I work for http://irondb.io, and have used Postgres for 18 years)