Execution plan quotes spill level 1

Question

Running a very simple query:

SELECT TOP 10 *
FROM WH.dbo.vw_data m
ORDER BY DateCompleted

Takes around 4 minutes.

96% of the execution is taken up by the following:

What does the warning mean and how is it interpretted?

The field DateCompleted isn't indexed: does this mean unless we hit an alternative field with an index, or add an index to DateCompleted it will always be slow?

Answer 1

Definitely index DateCompleted. You can see from the execution plan that 96% of the cost occurs when sorting this field, therefore it makes sense to add an index.

CREATE NONCLUSTERED INDEX IX_DATE_COMPLETED
    ON YourTable (DateCompleted); 

Answer 2

Sort Warnings are raised by SQL Server when a sort operation cannot be done in memory and must spill to tempdb

This article answers your question on Sort Warnings (link updated again, thanks to @quarkonium:

http://blogs.solidq.com/en/sqlserver/identifying-solving-sort-warnings-problems-sql-server/