November 14, 2006 at 9:32 am
Does anyone know how exactly the sub-tree cost is calculated and whether it is a sufficient metric for measuring query/stored procedure performance?
I used to think (although I could never find a single definitive source to state it clearly and precisely) that a sub-tree cost is some function of (reads + cpu time). However, my recent experience appears to challenge this belief.
Namely, I have a few versions of a stored procedure, where each version does the same thing, but differently.
Ver 1: # reads = 2 million and cpu_time = 19,707 and sub-tree cost = 0.1171
Ver 2: # reads = 1.5 million and cpu_time = 4,371 and sub-tree cost = 0.13
Ver 3: # reads = 154,000 and cpu_time = 935 and sub-tree cost = 0.25
Ver 4: # reads = 165,000 and cpu_time = 230 and sub-tree cost = 0.228
If I assume the sub-tree cost to be the benchmark, then I should go with Version 1. However, looking at other parameters, it it obviously the worst choice.
So, the question is, what is the best benchmark for judging performance ?
Thanks a lot
November 17, 2006 at 8:00 am
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December 1, 2006 at 10:24 am
An another website I was suggested to look at the following website, which does have a lot of information on the subject:
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