Hbase is going offheap as much as possible. Voltdb uses java for management and c++ for low-level.
They will write c++ in java eventually. Depending on how much performance you REALLY need.
The same for elasticseach, if you want performance you need to do the same thing scylladb did to cassandra (per-core-sharding, skip filesystem across cores etc)
In elasticsearcch terms, vespa.ai, which claims better performance/scalability/maintanability uses c++ for lucene layer and java for the solr/elasticsearch layer.
There are blog posts speeding lucene by 2x+ by changing some stuff to c/c++. There are libraries (trinity) claiming 2x+ performance .
There is google-engineer saying "bigtable is 3x faster than hbase" that I've read.
They will write c++ in java eventually. Depending on how much performance you REALLY need.
The same for elasticseach, if you want performance you need to do the same thing scylladb did to cassandra (per-core-sharding, skip filesystem across cores etc)