Can you point me at some? Because I've tried a few immutable data stores and been disappointed every time. Given about 10 GB of JSON structures, I keep finding things that can't outperform the boring combo of:

* Convert the versioned data to tab-separated values

* COPY it into Postgres every time

* Hope Postgres can act immutable enough even though it wasn't designed to be

The closest I've come to improving this situation was Kyoto Cabinet (unusable license) and rolling my own damn hashtable (it worked okay but adding new kinds of indexes was just unmaintainable, there's a reason databases should be made by experts).