What leads people to think this is related to the recent serialization format changes? And are there any more concrete suspicions on where exactly the problem occurs?
I'm not aware of any code in DataModel or the serialization components being unacceptably slow. There are various places where improvements could be made, though without data indicating that tackling such an instance would help us, this is really shooting in the dark. My suspicion is that the problem lies with the code that uses it. For instance there might be some code looping over a bunch of serializations to get a single sitelinks, and for each item use the regular entity deserializer. That'd be terribly inefficient. The issue would be that the code uses the regular entity deserializer rather than a suitable dedicated approach, not that the general entity deserializer is not tailored for this particular use case. Again, actual data on the problem, rather than suspicions, are needed to solve the issue.
> Thiemo was doing some benchmarking earlier, together with aude