Hi,
we're working on an upgrade (from 2008R2 to 2012) of a fairly large DB (12TB).
It's the question how SQL Server will behave after an upgrade...
After upgrading from 2008R2 to 2012 will there be “no statistics“ or just “not optimal“ statistics to support the first queries after the upgrade? So what will happen if “auto update statistics” is disabled and queries hit an upgraded 2012 server the first
time? Will query optimizer work like “there is no statistics” or will it use the 2008R2 statistics?
Will SQL 2012 initiate an “update statistics” (having auto update statistics enabled) immediately for the first query hitting an index when it finds only a 2008R2 statistic or will the rules for a “when to initiate an auto update statistics” still apply?
Will SQL 2012 after an upgrade from 2008R2 kick off multiple update statistics in parallel when a lot of queries hit the server the first time when “auto update statistics” (asynchronous mode) is enabled?
At the end it's the question how long the "downtime" (untill SQL server will work like before the upgrade, not just being "accessible again") will be...
Thomas Pagel
