Niko Neugebauer has two new posts up on columnstore index changes with SQL Server 2016.
Row Group merging & cleanup is a very long waited improvement that came out in SQL Server 2016. Once Microsoft has announced this functionality, everyone who has worked with SQL Server 2014 & Clustered Columnstore Indexes has rejoiced – one of the major problems with logical fragmentation because of the deleted data is solved! Amazing!
Just as a reminder – logical fragmentation is the process when we mark obsolete data in the Deleted Bitmap (in Columnstore Indexes there is no direct data removal from the compressed Segments with Delete command and Update command uses Deleted Bitmap as well marking old versions of rows as deleted).
Stretch DB or alternatively Stretch Database is a way of spreading your table between SQL Server (on-premises, VM in Azure) and a Azure SQLDatabase. This means that the dat of the table will shared between the SQL Server and the Azure SQLDatabase giving the opportunity to lower the total cost of the local storage, since Azure SQLDatabase is cheap relatively expensive storage typically used on the local SQL Server installations.
This mean that the table data will be separated intoHot Data & Cold Data, where Hot Data is the type of data that is frequently accessed and it extremely important (this is typically some OLTP data) and the Cold Data (this is typically rarely or almost never accessed archival or log data).
For the final user the experience should be the same as before – should he ask for some data that is not on the SQL Server, then it will be read from Azure SQLDatabase by the invocation of remote query, joined with the local results (if any) and then presented to the user.
These two posts are must-reads if you work with columnstore indexes.