Mysql: select from information_schema.STATISTICS hanging or slow? never saw a result I'm trying to check statistics with
    select from information_schema.STATISTICS
The query never ends. I have to stop it.

I checked innodb_stats_on_metadata=0 like in this post Solving INFORMATION_SCHEMA slowness, it was already set to 0.

Any idea?
I have more or less 20K tables and mysql 5.6.
Could this also give performance problem?
20K tables means opening 20K files on the system.  This takes minutes on the typical server.  How long did you wait?

20K tables often means poor schema design.

BTW, the slowness will be solved in 8.0, when the .frm files are moved into InnoDB tables.  Many I_S queries will be a hundred times as fast.