`Recommend Index` statements may be slow and can't be killed

[time-and-fate]

Enhancement

In a Recommend Index statement, for all related DBs in the queries, it will fetch all the table metadata in those DBs. When there are a lot of queries (1000 by default) or the user has lots of tables, this process costs many resources and time, especially with infoschema v2 now.

What's worse, during this process, there is no checkpoint for the timeout option or kill signal, so the user is not able to kill it, and the timeout option is also ineffective.