Comments on: CBO: the “non-empty result set” assumption

By: non zero values

non zero values — Wed, 24 Mar 2010 21:10:55 +0000

[...] with a zero simulation however they can if required be executed in a non zero simulation time. …Alberto Dell’Era’s Oracle blog CBO: the non-empty result …The CBO assumes that SELECT statements are always going to retrieve at least one row – even if this [...]

By: Alberto Dell’Era’s Oracle blog » CBO: “NewDensity” replaces “density” in 11g, 10.2.0.4 (densities part III)

Sun, 25 Oct 2009 17:46:07 +0000

[...] (class) of all possible equality filter predicate statements that hit the NPS, under the usual “non-empty result set assumption” and the further (strange and strong) assumption that the more a value is represented in the NPS, [...]

By: Alberto Dell’Era’s Oracle blog » CBO: the formula for the “density” column statistic (densities part II)

Sun, 25 Oct 2009 17:45:32 +0000

[...] is known to be not popular, hence hitting the NPS – remember that the CBO operates under the “non-empty result set assumption”, hence if the literal does not hit a popular value, it must hit a value of the [...]

By: Alberto Dell’Era’s Oracle blog » CBO: NewDensity for Frequency Histograms,11g-10.2.0.4 (densities part IV)

Fri, 23 Oct 2009 16:07:18 +0000

[...] statistics collection time, hence it returns the minimal cardinality estimate compatible with the non empty result set assumption (check this post for the importance of this assumption). If the statistics are reasonably fresh, [...]

By: Alberto Dell’Era’s Oracle blog » CBO: about the statistical definition of “cardinality” (densities part I)

Sat, 03 Oct 2009 10:32:28 +0000

[...] all values of :x for which w(:x) is non zero. At the other end of the spectrum, that is, under the non empty result set assumption, we have E[card] = sum ( w(:x) ) * num_rows / num_distinct(X) = num_rows / num_distinct(X), the [...]

By: Entradas de Oracle semanas 35-37 « Gruñidos sobre Oracle y SAP

Entradas de Oracle semanas 35-37 « Gruñidos sobre Oracle y SAP — Sun, 13 Sep 2009 11:42:49 +0000

[...] en SAP debe ser configurado según sus recomendaciones. Alberto Dell’Era nos explica que el CBO asume siempre que una sentencia SELECT devuelve por lo menos una fila. Acabo con un articulo interesante de Porus Homi Havewala, “Patch a Thousand Databases, Using [...]