Why finalise step is slow in immer ? Why is it more performant to setAutoFreeze to true?

[vsvamsi1]

🙋‍♂ Question

I have noticed the finalise step in a "produce" to be quiet slow and i was looking out to see if there are any alternative libraries to immer which is faster. I have come across a library called mutative, in that they have stated the following about immer

But its performance issue causes a runtime performance overhead. Immer must have auto-freeze enabled by default(Performance will be worse if auto-freeze is disabled), such immutable state with Immer is not common. In scenarios such as cross-processing, remote data transfer, etc., these immutable data must be constantly frozen.

I noticed the same, the performance of immer improving after setting autoFreeze is true. I was wondering why does this happen, isn't there a cost associated to freezing? What affects the finalise step of a draft in a produce?

[mweststrate]

Immer currently scans the returned object tree from a producer to see if there is a draft lurking somewhere in there, to finalize it. However, it will skip any part of the tree that is frozen (since it can't have changed since the previous produce run). So autofreezing is a bit more expensive when the data "enters" the state tree, but cheaper thereafter.

I intended to claw back the performance drops of Immer in #1152, just need a big chunk of time somewhere to get started, which I'm lacking at the moment :)