Many banks, hedge funds use kdb+/q for time series databases. This (very expensive) software is literally unheard of outside of these niche domains. I've been using it for close to 5 years for high frequency data, and honestly nothing out there comes close to this awesomeness of kdb+
I would be interested to hear what you consider high volume (writes/second). I am supporting a manufacturing system and it sits at the moment at 7 000 writes/second (it is a normal time series, ie id,time,value,quality).
7000 writes per-second is pretty low for many high-volume time series needs.
Though it's not usually write throughput that most of these technologies are worried about. It's usually compression using dsp methods, aggregate stream folding computations, etc... that matters.
The systems I deal with start at millions of writes per second and go up from there. I have heard of systems that do over a billion writes per second, though I have not breached that threshold personally (yet).
From an IoT or sensor network standpoint, 7000 writes/second is an idle server.
I don't have numbers handy. The real power of kdb+/q comes from the column oriented architecture and the extremely powerful vector functional language q. The language q is inspired by APL. I highly recommend you to check out this article to get a sense of the APL family of languages https://scottlocklin.wordpress.com/2013/07/28/ruins-of-forgo...
If you want a database for blazing fast data-storage and retrieval, there are many options available. You start seeing the real benefits of kdb+/q when you use q to simplify very complex operations that aren't easily done in SQL. Also, the high level operators that q makes your code extremely terse. I've written complex backtesting systems that perform data mining on massive datasets - all in one page of very tight q code!
There is a free 32bit version of kdb available (http://kx.com/software-download.php). For the commercial version, pricing information is not publically available.
The thing with KDB is almost all uses of it are in memory deployments. It isn't hard to make something that has little persistence or relegates persistence to a 2nd class citizen to run quickly.
