Archive for October, 2009

CBO: NewDensity for Frequency Histograms,11g-10.2.0.4 (densities part IV)

As we have seen in the previous posts of this series, in 11g a new figure named “NewDensity” has been introduced as a replacement for the “density” column statistic for columns whose histogram has been collected; this change has been backported in 10.2.0.4 also. In the...
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CBO: “NewDensity” replaces “density” in 11g, 10.2.0.4 (densities part III)

In this post we are going to explore and explain the rationale for the formula used by the CBO to compute the “NewDensity” figure that replaces, from 10.2.0.4 onwards, the “density” column statistic in the cardinality estimation formulae for columns with height-balanced (HB)...
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CBO: the formula for the “density” column statistic (densities part II)

In this post we are going to explore and explain the rationale for the formula used by dbms_stats to compute the “density” column statistic, used by the CBO in versions less than 10.2.0.4 to estimate the cardinality of a class of SQL statements. In the next post, we will speak about its...
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CBO: about the statistical definition of “cardinality” (densities part I)

Let’s explore the concept of cardinality from the point of view of the statistician; this is both to get a clearer vision of the matter (i.e. for fun) and to path the way for understanding the rationale for the “density” statistics as calculated by dbms_stats (the topic of an...
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