April, 2010

(more SQL Bits questions) Does the SQL Server Query Optimizer consider index fragmentation in plan selection?    No, it does not directly care.  The optimizer does currently consider the number of pages consumed by the index.  So,...

A question from two of the MVPs: Are these two queries conceptually the same? select a.id, b.id, c.id from A left join C on A.id = C.id left join B on A.id = B.id;   select a.id, b.id, c.id from A left join B on A.id = B.id left join C on A.id =...

In my prior post, I introduced the concept of runtime constants.  Now let’s take this and apply the concept further to the topic of matching scalar predicates to indexes.   I will paraphrase a customer question I was mailed after SQL Bits last...

(more questions resulting from SQL Bits – some of these answers will be a bit more terse than my usual verbose self :))   A customer asked a different question and I need to introduce a concept to you before I can answer that question, so I will...

I got a few requests for additional topics where one can read about the SQL Server query optimizer’s search framework (which happens to be called Cascades).  I will warn you that most of these are academic papers.  Some of these use different...

One question I received at SQL Bits had to do with a reasonable programming practice that has an unintended performance impact.   SELECT <something> FROM T WHERE (@p is NULL or col = @p)   This pattern is common and we call it the “optional...

Greetings all.  I just had a fascinating week.  I was invited to go give a talk at the SQLBits conference in London, England and I flew over on Wednesday/Thursday for a talk on Friday.  I was supposed to leave on Saturday but found myself...