[lovelearning]

At one point, their search used LucidWorks Fusion [1], a commercial product based around Solr (that uses Lucene indexes under the hood) but also integrates a vector database and the like for semantic search. The linked wiki page still has Lucene-style queries.

[1]: https://lucidworks.com/customers/reddit/

[tmikaeld]

That's kind of my point, Solr and Lucene put the index in memory.

[omegalulw]

Can't the index be shared across a cluster? Possibly with multiple replicas for a share to allow for servers to easily go up and down?

[tmikaeld]

It can, but that would be slow and cost would be prohibitive.

[kevincox]

Really? It's just a bit of text. RAM is fairly cheap these days.

[liveoneggs]

not the entire index, only what is needed for each query.