Answer
A spill happens when the memory grant is too small and SQL Server must offload intermediate data to TempDB.
Common causes: inaccurate cardinality estimation, heavy sorts, hash joins, window functions.
Quick Answer
A spill to TempDB happens when SQL Server allocated less memory than a sort or hash operation actually needed. Overflow data is written to TempDB disk, which is orders of magnitude slower than memory. Caused by underestimated row counts (bad statistics). Look for sort warnings and hash warnings in execution plans.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ