What restricts the growth of the "tangle"

Question

In IOTA, each transactions are created by a node performing a fixed POW verification on two other transactions. Since the POW difficulty is never adjusted, node(s) ability to create transactions scales linearly with the amount of hashing power they have.

This means that the "tangle" can grow as large as the amount of hashing power available to it, which can make it hard for new nodes to sync to the network and existing nodes to keep up (classic blockchain scaling argument). So how does IOTA deal with this without using the coordinator?

I know that the coordinator can a) take snapshots and b) is rate limiting the transactions per second, but this does not seem to be a sufficient solution if they ever want to move away from using the coordinator which is a central point of failure and is often brought up as a criticism against IOTA and how decentralized it really is.

Answer 1

Since the POW difficulty is never adjusted,

The difficulty could be adjusted if there was a reason for it - and it was adjusted in the past. Also the testnet has a lower minimum weight magnitude (=difficulty).

the "tangle" can grow as large as the amount of hashing power available to it

The tangle will grow as fast as the amount of hashing power used to make transactions. Not all the hashing power that would be available is used. Whenever somebody wants to send a transaction + does the proof of work, the tangle grows.

I know that the coordinator can a) take snapshots

In the future, every node will be able to decide whether to store certain transactions (e.g. 0-value-trasactions) or not and whether and when to make snapshots or not.

I know that the coordinator b) is rate limiting the transactions per second

The coordinator is not rate limiting the transactions per second if the transactions are good transactions. (We don't know how exactly the COO determines the difference between good and bad transactions because it isn't open source yet)

If somebody sends 1000 transactions per second to perform some kind of attack, the coordinator doesn't confirm those bad transactions.