May 17th, 2013 by Alberto Dell'Era

This post is a brief discussion about the advantages of activating parallelism by altering the session environment instead of using the alternative ways (hints, DDL). The latter ways are the most popular in my experience, but I have noticed that their popularity is actually due, quite frequently,...

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August 27th, 2012 by Alberto Dell'Era

One of the most useful information that the Oracle kernel attaches to plans in the library cache are measures of various resource consumption figures, such as elapsed time, consistent and current gets, disk reads, etcetera. These can be made available for each plan line (aka “row source...

Read morePosted in CBO, performance tuning, xplan | 12 comments

October 23rd, 2009 by Alberto Dell'Era

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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October 16th, 2009 by Alberto Dell'Era

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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October 10th, 2009 by Alberto Dell'Era

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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