> Ever-growing state: for CRDTs to work well they need to keep a record of both what exists, and what has been deleted (so that the deletes aren’t accidentally

> Ever-growing state: for CRDTs to work well they need to keep a record of both what exists, and what has been deleted (so that the deletes aren’t accidentally added back in later). This means that CRDT state will continually expand. I guess a couple things: It depends on the CRDT. Some CRDTs grow with the number of replicas and others with the number of events. State-based CRDTs don't need to keep history and don't need causal ordering of messages, but internal bookkeeping grows with the number of replicas. And for large states (like sets and maps), it can be prohibitive to send the state all over the wire for an idempotent merge. That's why in practice, people implement Op-based CRDTs, which makes the trade: in order to send small ops over the wire, we now need causal ordering of messages. To make sure we can sync with replicas long offline, we keep as much history so that they can catch up. There are other variations, such as delta-state based CRDTs that send diffs, and merkle CRDTs, which use merkle data structures to calculate diffs and detect concurrency, which have different growth characteristics. --- As for a growing state: Is this actually a concern for devs that aren't using CRDTs for collaborative text? I can see that being an issue with the amount of changes that can happen. But outside of that, lots of data don't grow that fast. We all regularly use Git and it keeps a history of everything. Our disks are huge, and having an immutable record is great for lots of things (providing you can access it). > Opaque state: ...you’re generally left with an opaque blob of binary encoded data. Most CRDT libraries take a document-orientated angle. It assumes that you can contain the entire "unit of work", like a document, inside of a CRDT. However, if your data is more relational, it doesn't quite fit. And while there's immutable data in a CRDT, I do wish it was more accessible and queryable. In addition, being a binary blob, it's not exactly composable. I think CRDT libraries should be composable with each other.