Neater way of dynamically selecting a database other than sp_executesql - sql-server

Question

I am looking to set up a high availability architecture whereby two mirror databases exist (DB1 & DB2) that serve another database with views (DBV) on it. DB1 has the overnight ETL on it, whilst DBV looks at DB2 until the etl is complete on DB1, at which point its views switch to the underlying tables on DB1. Once the ETL is complete on DB1, DB2 is restored with DB1 data before the next day's ETL. The next day, DB1 and DB2 switch roles.
I am looking for a neater/more secure way of switching between the two views than running sp_executesql to run a dynamically built string. I will be looking to also do this on stored procedures from a staging database which need to have their scripts dynamically altered to use the correct database to run the ETL on. Essentially, I am looking to pass the USE statement dynamically and then execute the rest of the script outside of any dynamic statement.
I want to avoid sp_executesql for support reasons for other developers and also to get around any possible extensive concatenation of strings if the stored procedure/view gets particularly lengthy.
Any ideas / different approaches to high availability in this context would be welcome.

Answer 1

One option might be to create a copy of each view in DBV for both target databases - i.e.
some_schema.DB1_myview
some_schema.DB2_myview
and then use a synonym to expose the views under their final names.
CREATE SYNONYM some_schema.myview ON some_schema.DB1_myview
Your switch process would then need only to drop and recreate the synonyms, rather than the views themselves. This would still need to be done with a dynamic SQL statement, but the complexity would be much lower.
A downside would be that there would be a risk of the definitions of the underlying views getting out of sync.
Edit
At the cost of more risk of getting out of sync, it would be possible to avoid dynamic SQL altogether by creating (for instance) a pair of stored procedures each of which generated the synonyms for one database or the other. Your switch code would then only need to work out which procedure to call.

Answer 2

Have you considered renaming the databases as you switch things around? I.e. the following prints 1 followed by 2, nothing in DBV had to be modified:
create database DB1
go
use DB1
go
create table T (ID int not null);
insert into T(ID) values (1);
go
create database DB2
go
use DB2
go
create table T (ID int not null);
insert into T(ID) values (2);
go
create database DBV
go
use DBV
go
create view V
as
select ID
from DB1..T
go
select * from V
go
alter database DB1 modify name = DBt
go
alter database DB2 modify name = DB1
go
alter database DBt modify name = DB2
go
select * from V
Obviously better names than 1 and 2 may be used. This way, DB1 is always the one used for live and DB2 is used for any staging work.