[Maria-discuss] How many open files by daemon is still sane?

Hey, with limited experiences with mariadb deployments, I'm wondering how many open files by the mysqld daemon is still sane (expected). We have a customer that reports hundreds of thousands of open files with 600 connections (thread_pool_max_threads is used). Those processes seem rather stalled, but files in the datadir are often opened 40.000 times. Is it even possible that one file is opened several times during processing one query? Or does it mean there are ~40.000 queries running? Version of MariaDB: 5.5.40 Honza