Tag: cbo

Home Tag: cbo

Strange things with the Oracle optimizer

May072018Freek D'Hoogecbo, Oracle optimizer

Recently I needed to investigate a performance problem for 2 customers, which turned out to be problematic execution plans. It had the smell of Oracle optimizer bugs all over them. Although the first one is maybe somewhat self-inflicted injury. Both environments were using Oracle 12.1.0.2 with the October 2017 patch set. Case 1: functions on…

DOP and explain plan notes

Aug042016Freek D'Hooge12c, cbo, explain plan, oracle, parallel query

Earlier this week I was discussing some parallel server parameters with a client, when I noticed something strange. It looked like Oracle was upholding the parallel slave limits set in the parallel_degree_limit parameter, while the parallel_degree_policy was set to manual. According to the documentation, this parameter should not be active with the parallel_degree_policy set to…