summary

Generate_statistics grows QueryStatistics ConcurrentHashMap indefinitely

Description

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:

public void query(int id, int userId) {
		// ...
		CriteriaBuilder builder = session.getCriteriaBuilder();
		CriteriaQuery<InboxMessage> query = builder.createQuery(InboxMessage.class);
		Root<InboxMessage> root = query.from(InboxMessage.class);
		query.where(builder.and(
			builder.equal(root.get(InboxMessage_.id), id)),
			builder.equal(root.get(InboxMessage_.inboxUser).get("id"), userId));
		// ...
	}

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: