SQL Server supported Linked Servers for years. Now Microsoft is letting us know this capability is going to be deprecated in a future release. When they do stop supporting linked servers, what will be the impact on you?
For the un-initiated, a linked server may be created on an instance of SQL Server allowing access to an external SQL source. That source may be another instance, or even the same instance, of SQL Server. however, it may be another database engine or even Active Directory, All that is required is a valid ADO accessable device.
There are some issues you should understand. When executing a query on a remote linked server, even if it is SQL Server, the query plan cannot take advantage of indexes or statistics to find the best way to resolve your query. I have seen queries that often simply perform a table scan, which may not be efficient, especially on large tables.
When you end up with sharded data where the fulfillment of data requests crosses multiple instances of SQL Server, the best performing technique is to perform queries on each database separately, and handle the heterogeneous aspects locally in a different application. For SQL Azure this is your only option.
So, what are you going to do? Are you going to stop sharding your data and put it all into a single large database so Heterogeneous queries are not required? Are you going to do the joins in a data access layer? Are ykou going to stop upgrading when remote queries are no longer supported? Is this really just not a problem for most of us?
Share your thoughts or plans online or in email to btaylor@sswug.org.
Cheers,
Ben