The order of attributes in Json might matter as far as I can remember, so LinkedHashMap might not be replaceable with a concurrenthashmap.
Plus concurrenthashmap is not exactly without concurrency overhead…
I wrote a util that creates a immutable schema <>
But you would have to use it it conjunction with a unsynchronized avro implementation. (which I do in my fork, and you can do as well).

I wonder if there is interest in merging this into the avro lib someday.

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