Anything that represents numeric values as text will be an order of magnitude slower to deserialize than a binary format. I don’t have a published benchmark but in my testing which is easy to replicate I’m storing an array of around 50 million uint64 values in a contiguous block of data to maximize deserialization speed. Just to get a sense of the difference I also tested using a JSON array as a more user friendly storage format and the penalty of deserializing the JSON and populating the array was around 20x in runtime cost in my use case. The platforms I tested on were C# and Java.