When To Use DBCC DROPCLEANBUFFERS When You're Tuning SQL Server Queries
In this video, I delve into the question of how to determine if a query tuning effort has been successful. Often, clients ask me, "Did my query really get faster?" To address this, we explore various techniques such as using recompile hints, tweaking cardinality estimation models, and employing temp tables or table variables. However, one powerful method is utilizing the 'DBCC DROPCLEANBUFFERS' command to simulate a clean buffer pool state, which can highlight whether memory constraints are affecting query performance. I walk through an example where running this command reveals significant differences in query execution times, indicating that memory might be the limiting factor rather than parameter sniffing or other issues. By understanding these nuances, you can better assess the effectiveness of your tuning efforts and make informed decisions about hardware upgrades or index optimizations.
CHAPTERS
00:00:00 - Introduction
00:01:24 - Dump CTE into Temp Table
00:02:04 - Query Optimization Decisions
00:03:13 - Parameter Sniffing Issue
00:05:39 - Repeated Queries Discussion
00:06:18 - Parameter Sniffing Check
00:07:32 - Query Performance Variability
00:08:48 - Resource Usage and IO
00:09:04 - Index Considerations
00:10:04 - Disk Read Impact
00:11:29 - Weight Stats Analysis
00:12:17 - Memory and Performance
00:13:04 - Server Situation Proof
00:14:05 - Query Tuning Tools
00:15:16 - Hardware Impact
00:16:00 - Cardinality Estimation Hints
00:17:02 - Thank You
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