I am currently running Apache Pulsar for the Noswhere indexer and it works pretty well.
Discussion
That is also the basis of the event bus for NFDB relays, in non-persistent mode.
NFDB alone depends on 6 data stores, and has about 10 internal components
Sounds complicated until you try to store TBs of events cached all across the world, while maintaining high throughput, low cost, and supporting features like SmartCache and IA.
So yes, you can dump TBs of (public-domain) books into it, and it won’t care.