[masklinn]

I don't believe that's the case (an other commenter notes they run solr processes up to 160GB), however they may have run into the compressed oops optimisation, or more precisely the end of it: because Java is a very pointer-heavy language, if the maximum heap size is under 32GB many 64b JVMs use a variant of tagged pointers where they have 35 bit pointers stored in 32 bits (since the lower 3 bits are always empty they can shift them in/out).

Except once you breach the 32GB limit, your 32 bit pointers grow to 64, and depending on your application you might need to grow your maximum heap into the high 40s to get room for new objects: https://blog.codecentric.de/en/2014/02/35gb-heap-less-32gb-j...