SQL Server Performance Tuning

How We Made T-SQL Queries Run 589x Faster

Mark Varnas
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Here is what can be done during a session of SQL performance tuning.

Improvement after tuning







Minimize indexing for faster SQL Server performance; excess indexes slow it down.


The stored procedure below was one of the most called on the client’s SQL Server.

The procedure was overusing resources:

  • Duration: 227 ms
  • Average CPU: 50 ms
  • Disk, number of disk reads: 2,496

The solution

Here is how we improved that:

  • Dropped the [IX_ClientID_OrderDate]
  • Added the index [IX_ClientID_OrderDate_WorkOrderNumber]

That’s it! That simple!

Before vs. after

Here’s the before-and-after snapshot that showcases the efficiency gains:

We took 5 separate runs to analyze after the fix:

(8k page reads)
Run 128916312,4968
Run 29913112,4968
Run 311413112,4968
Run 431416312,4968
Run 532216212,4969

Disk, number of reads

Before tuning
After tuning

Before TuningAfter TuningImprovement (%)Improvement (X)
Overall improvement:58,900% faster589x faster
*The numbers are an average of multiple T-SQL [GetNextWorkOrderNumberByGroupID] runs.

Clearly, with just a few tweaks to indexing, the query execution time plummeted by 589 times!

Duration, ms

Before tuning
After tuning

Why do you merge two indexes into a single one?

Because indexing is not free. The fewer indexes you can get away with, the faster your SQL Server runs.

Indexes can greatly improve query performance in the SQL Server, but they may hamper the performance too.

So, it’s very important to understand your overall workload and find a good balance between making your queries efficient and not paying too much for that.

See more SQL Server Performance Optimization examples here.

Article by
Mark Varnas
Founder | CEO | SQL Veteran
Hey, I'm Mark, one of the guys behind Red9. I make a living performance tuning SQL Servers and making them more stable. I channel my SQL into our SQL Managed Services, SQL Consulting and our internal database products.

Managed SQL Server services, consulting, and emergency support from expert DBAs to improve performance, predictability, and cost.

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