We have a multi-column primary key with an auto-increment column as
the 3rd column in the primary key in InnoDB.
Is there a requirement to have the auto-increment column as the
leftmost column in the primary key in order for InnoDB to cluster by
the multi-column primary key?
I don't believe this to be the case but there has been some discussion
on this topic.
I haven't been able to find any definitive answers.
Judging by the query profiling results and explain output, we are
seeing the benefits of clustering by primary key.
If you have any insight on this matter, it would be much appreciated.