Your question is ambiguous. Comparing RavenDb to SQL on the matter of efficiency is not relevant. Efficiency itself is ambiguous here. However..!
A well designed Lucene index (basic/core mechanics of RavenDb) will likely perform better than a stored procedure (especially if infested with logic). So basically, potentially faster.
Also, it will help extracting that logic (if any) to where it belongs.
The C# API is amazing…
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solved RavenDB: efficient enough? [closed]