Want a Slow Website? Use InnoDB
I have many web-apps running online, and most are supported by a MySQL backend, with tables using the InnoDB engine.
InnoDB is great, it enforces data-integrity with foreign keys, not like MyISAM that doesn't give a damn.
When I recently benchmarked a particular web-app, I noticed one update query taking approximately 0.45 seconds. This was simply to update the user table to set the last-login field.
UPDATE user SET last_login = ? WHERE ( id = ? ) : '2015-06-01 17:57:03', '2' Took: 0.456952 seconds
The user table has less than 200 rows, and 5 columns.
It did however have 11 foreign keys linking to it, so I quickly dropped those, and finally converted the table to MyISAM.
mysql> alter table user engine=myisam;
Which reduced timings ever so slightly!
UPDATE user SET last_login = ? WHERE ( id = ? ) : '2015-06-01 19:24:16', '2' Took: 0.000180 seconds
I'm using DBIx::Class in Perl when dealing with the database, so relationships are configured to deal with cascading of deletes in the app, saving the database engine the job.
For high-performance web-apps InnoDB doesn't appear to be the best idea in the world.