One thing which is quite hard to do in Datomic is simple pagination on a large sorted dataset, as one can easily do with LIMIT/OFFSET in MySQL for example. There are solutions for some of the cases, but general case is not solved, as far as I remember (it’s been a while I used it extensively)
It depends! If you want to lazily walk data, you can read directly from the index (keep in mind, the index = the data = lives in your app), or use the index-pull API which is a bit more convenient.
However, if you want to paginate data that you need to sort first, and the data isn't sorted the way you want in the index, you have to read all of the data first, and then sort it. But this is also what a database server would need to do :)
Yep, I am well aware of these specifics and workarounds, but in general case where is no general solution to the question asked here, for example [0].
And for big datasets with complex sorting it will take some effort to implement a seemingly simple feature.
Guess it is just one of the tradeoffs, as while some features Datomic has out of the box are hard to replicate in RDBMS-es, things like pagination which are often took for granted is a bit of work to do in Datomic. So it is something to keep in mind when considering the switch
Datomic's covering indexes are heavily based on their built-in ordering, and doesn't really have much flexibility in different ways to sort and walk data.
Personally, I'm a fan of hybrid database approaches. In the world of serverless, I really enjoy the combo of DynamoDB and Elasticsearch, for example, where Dynamo handles everything that's performance critical, and Elasticsearch handles everything where dynamic queries (and ordering, and aggregation, and ....) is required. I've never done this with Datomic, but I'd imagine mirroring the "current" value of entities without historical data is relatively easy to set up.
