I disagree that any serious installation is using innodb_file_per_table. It does have downsides. In our use case we're making very heavy usage of table partiti

I disagree that any serious installation is using innodb_file_per_table. It does have downsides. In our use case we're making very heavy usage of table partitioning (over 500 partitions for some of our very large tables). Because each partition is effectively another table under the covers, if we were to use innodb_file_per_table then we'd have tens of thousands of files. This means a lot more file handles being opened/closed (as well as the obvious ulimit gotchas for the uninitiated). This noticeably hampered query performance when seeking data from random partitions.