Unused Indexes Might Not Be

Tara Kizer has a warning for people eager to drop “unused” indexes:

About 10 years ago, I decided to drop an unused index on a table that had 2 billion rows. The database was around 7TB in size. We were having storage and performance issues. I thought I could help the system out if I were to drop the index.

4 days after I dropped the index, I got a call from our NOC that CPU utilization was pegged at 100% for an hour so they were reaching out to the on-call DBA to check it out. I logged in and saw a query using A LOT of CPU. Its WHERE clause matched the index I had dropped. The execution plan showed it was scanning the table.

It turned out that I only had 2 weeks of uptime, which didn’t include the 1st of the month. The query that was causing the high CPU utilization was a report that ran on the 1st of each month.

Tara has also provided us with a script to track these details over time, so check that out.

Related Posts

Putting TempDB Files On Azure IaaS D Drive

John McCormack tries out using the temporary drive on Azure VMs for tempdb: Azure warn you not to to store data on the D drive in Azure VMs, but following this advice could mean you are missing out on some very fast local storage. It’s good general advice because this local storage is not permanently […]

Read More

Sizing Azure SQL Database

Arun Sirpal takes us through finding the right size for Azure SQL Database: Do you want to identify the correct Service Tier and Compute Size ( was once known as performance level) for your Azure SQL Database? How would you go about it? Would you use the DTU (Database Transaction Unit) calculator? What about the […]

Read More

Categories

October 2018
MTWTFSS
« Sep Nov »
1234567
891011121314
15161718192021
22232425262728
293031