Plan Explorer Row Estimates

Joey D’Antoni shows how in SQL Sentry Plan Explorer, estimated counts can differ from what SSMS shows:

I quickly honed into the fact that the bad query was doing a lazy spool with 6 BILLION rows versus the 229 million in the good query. However, my friend who was looking at Management Studio was asking where I was getting those numbers. This is what the XML from the original plan showed:

<RelOp AvgRowSize=”51″ EstimateCPU=”0.00889634″ EstimateIO=”0.01″ EstimateRebinds=”0″ EstimateRewinds=”139581″ EstimatedExecutionMode=”Row” EstimateRows=”48868″
LogicalOp=”Lazy Spool” NodeId=”55″ Parallel=”true” PhysicalOp=”Table Spool” EstimatedTotalSubtreeCost=”1242.86″>

This is a helpful feature in scenarios like this, where operator weight is skewed because it only shows a single run but in reality happens more than once.

Related Posts

When AT TIME ZONE Is Too Slow

Robert Davis troubleshoots a performance problem relating to time zones: Time Zones were definitely being a drag today. I got an email from one of the developers at work asking about the performance difference between 2 queries. The only difference between the 2 queries is that one of them uses the AT TIME ZONE clause that was […]

Read More

When Join Order Matters

Bert Wagner takes a look at one of the lesser appreciated tricks in performance tuning: I had a great question submitted to me (thank you Brandman!) that I thought would make for a good blog post: …I’ve been wondering if it really matters from a performance standpoint where I start my queries. For example, if […]

Read More

Categories

February 2016
MTWTFSS
« Jan Mar »
1234567
891011121314
15161718192021
22232425262728
29