October 20, 2015 at 4:04 am
When working with this, what measurement are the fields in? Is it milliseconds ?
avg_user_impact and avg_total_user_cost
October 20, 2015 at 4:13 am
Just answered my own question on the avg_user_impact column, that's a %.
if someone could clarify if avg_total_user_cost is MS then that would be great.
October 20, 2015 at 4:20 am
Cost is not in milliseconds. It's a unit-less number that is only useful for comparing with other costs. It's an amalgam of the CPU, IO, duration, memory, etc estimated by the query optimiser.
A higher cost query will use more resources than a lower cost query, that's about all you can say.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability
October 20, 2015 at 4:27 am
The cost is a relative number without any units or range associated with it.
The optimizer assigns a cost to every execution plan it creates , think of it as a number to indicate the amount of effort involved.
So a query can have a cost of 20 right now the thing to keep in mind is its not 20 out of 100 or even thousand its just 20.
After the index is created the cost of the query can come down to say 5 , this change is what is captured with avg _total_user_cost, as defined by BOL
Average cost of the user queries that could be reduced by the index in the group.
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