In the final part of this series I want to cover one last source of Parallel Execution Skew: Skew caused by Outer Joins. If you have Outer Joins where the majority of foreign key values is NULL, this can lead to the following symptoms: From a processing point of view for a parallel outer join, the NULL value in the foreign… Read more
After providing a baseline for Parallel Execution working as expected in the introduction of this series, in this part I’ll demonstrate how things can go wrong with the work distribution. A Simple Example Of Parallel Execution Skew One common source of Parallel Execution Skew is a skewed foreign key, which means that the value distribution of the foreign key column… Read more
This is the first part of a mini-series about Parallel Execution Skew and how to address it. Introduction So what does “Parallel Execution Skew” mean? With Oracle Enterprise Edition you can have Oracle automatically spread the processing of a single SQL statement across several worker processes in the hope to complete the processing in less elapsed wall-clock time. Note: T… Read more
