New version of the VATS algorithm (Largest Dependency Set First)

[sensssz]

This pull request uses a new version of the VATS algorithm under version 5.7.

[grooverdan]

what is different about the new implementation?

[mysql-oca-bot]

Hi, thank you for your contribution. Please confirm this code is submitted under the terms of the OCA (Oracle's Contribution Agreement) you have previously signed by cutting and pasting the following text as a comment:
"I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it."
Thanks

[sensssz]

Hi, Daniel. In this new implementation we look at the sub-tree of each lock instead of just looking at the arrival time in the system. This gives us a more accurate yet efficient enough way of deciding which transaction to schedule first.

[sensssz]

I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

[grooverdan]

@sensssz , great, keep up the good work! 👍

[mysql-oca-bot]

Hi, thank you for your contribution. Your code has been assigned to an internal queue. Please follow
bug http://bugs.mysql.com/bug.php?id=84266 for updates.
Thanks