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latch：cache buffers chains的优化思路
数据块在buffer cache存放是以linked list方式存放的。当一个session想要访问/修改buffer cache的block,首先需要通过hash算法检查该block是否存在于buffer cache中，检查相同的SQL语句是否存在于library cache中也是通过hash算法实现的。要判断block是否存在于buffer cache中，就需要扫描linked list(此...
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LNNVL官方解释
LNNVL官方解释LNNVL provides a concise way to evaluate a condition when one or both operands of the condition may be null. The function can be used only in the WHERE clause of a query. It takes as an argument a condition and returns TRUE if the condition is FALSE or UNKNOWN and FALSE if the condit...
