Earlier today, I was working with a developer on a query that had poor performance. This query was large and complex, and initially it looked like a daunting effort to find out where the performance problem lies. With Explain Plan we can sometimes use the cost to help narrow down the performance pain point of a large, complex query.
Looking at an Explain Plan of this query, we can see its overall cost is pretty high.
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The overall cost is only a little more than the cost to access this table. It is clear that the FTS on this table is largest contributor to the pain point of this query being analyzed.
By looking at the Explain Plan costs in this manner, we were able to very quickly focus in on the one area of a very complex query that is causing the most performance pain. Without the cost analysis done here, determining which portion of the query below is causing problem would have been a lot of work.
