Generate_statistics grows QueryStatistics ConcurrentHashMap indefinitely

We've encountered a problem with the generate_statistics configuration in production.

The ConcurrentStatisticsImpl uses a ConcurrentHashMap that saves the statistics for all the HQL queries that are executed. However from our application we generate a lot of unique query HQL queries because we use the JPA query builder, and something like this:

creates a new query string for each new input.

This is problematic because the map only grows, and after a couple of days our application consumes too much memory.

It seems possible to clear the stats periodically, however:

• the default behavior 'leaks' memory

• it's not documented

So perhaps it'd be better to have a default max_size option or something to limit the size of the queryStatistics.

Link to discourse: https://discourse.hibernate.org/t/generate-statistics-grows-querystatistics-concurrenthashmap-indefinitely/1287