Relational_Database_Index_Design_and_the_Optimizers

Relational databases have been around now for more than 20 years. In their early days, performance problems were widespread due to limited hardware resources and immature optimizers, and so performance was a priority consideration. The situation is very different nowadays; hardware and software have advanced beyond all recognition. It’s hardly surprising that performance is now assumed to be able to take care of itself! But the reality is that despite the huge growth in resources, even greater growth has been seen in the amount of information that is now available and what needs to be done with this information. Additionally, one crucial aspect of the hardware has not kept pace with the times: Disks have certainly become larger and incredibly cheap, but they are still relatively slow with regards to their ability to directly access data. Consequently many of the old problems haven’t actually gone away—they have just changed their appearance. Some of these problems can have enormous implications— stories abound of “simple” queries that might have been expected to take a fraction of a second appear to be quite happy to take several minutes or even longer; this despite all the books that tell us how to code queries properly and how to organize the tables and what rules to follow to put the right columns into the indexes. So it is abundantly clear that there is a need for a book that goes beyond the usual boundaries and really starts to think about why so many people are still having so many problems today.