CDNs, caching (such as with memcached or redis), and read-only MySQL slave servers can scale Drupal for anonymous, read-only traffic. However, these approaches do not help
scale Drupal to handle increased dynamic page generation (such as for logged-in users) or heavy write loads (such as high comment volume). Also, Drupal 7's support for read-only slave servers is incomplete, with many contrib modules not supporting it at all.

At this BOF, we will describe our solution for horizontally scaling MySQL in a way that allows elastically scalable read and write capacity while maintaining 100% compatibility
with existing Drupal core and all contrib modules.