Hi folks:
I see a node named "Bookmark Lookup" in my execution plan.
What does it means? It costs most among steps inside the plan. Any suggestion to optimize it?
+1
A:
It means the optimiser uses a non-clustered (NC) index first, then uses the NC->C pointer/bookmark into the clustered index (which is your data) to get more data. And yes, it's expensive usually.
You'd use a "covering index" to remove the lookup so all data part of the NC index (the link explains what I've just said above too)
gbn
2010-03-12 09:36:40
+1
A:
You might find this free ebook from Redgate useful http://downloads.red-gate.com/ebooks/HighPerformanceSQL_ebook.zip
Martin Smith
2010-03-12 09:38:38