I'm an architect working on a project to rebuild our current consumer site, possibly using Drupal, and am new to Drupal and learning as much as I can as fast as I can. I see that one of the things that's been added in D7 is support for master/slave DB configurations, so I wanted to get more info. about that.
I've found in the DB documentation that 1) slave DBs can be specified in the DB configuration (http://drupal.org/node/310071), and 2) that module writers can pass an optional 3rd argument to db_query() to mark queries that are save to send to slaves (http://drupal.org/node/310072). Were there any other slave-related changes made in D7 and if so, what were they?
Since 2) requires code changes to modules, I'm curious how much progress has been made in updating code to mark slave-safe queries. Can anyone speak to the extent to which that's been done in core modules and contrib modules?
And can anyone post sample stats from slave-using installations as to what percentage of queries are seen going to slaves?