Github user mikaelstaldal commented on the issue:
https://github.com/apache/logging-log4j2/pull/110
@mdvorak I think that we should not care so much about garbage and micro
optimizations in the Jackson based layouts, since they are far from
garbage-free or optimal anyway.
Keep it as is, and don't bother with ThreadLocals.
If we want to make JsonLayout garbage-free, we would have to stop using
Jackson and do something similar to GelfLayout.---
