(1)sort 算子,会显示排序信息 Sort Method代表排序的方法,包括quicksort(快排)和disksort(外排)。快排即内存够用时,所有的排序操作均在内存中完成,外排说明当前可用内存不足,需要下盘。 (2)hashjoin算子 Buckets:代表hash表中实际使用的桶的个数 Batches:代表hashjoin中实际分块的数量。如果Batches=1,则说明所有...
filesort使用的算法是QuickSort,即对需要排序的记录生成元数据进行分块排序,然后再使用mergesort方法合并块。其中filesort可以使用的内存空间大小为参数sort_buffer_size的值,默认为2M。当排序记录太多sort_buffer_size不够用时,mysql会使用临时文件来存放各个分块,然后各个分块排序后再多次合并分块最终全局完成排序。 Us...
这个filesort是说, MySQL要多做一次额外的排序, 确切的说是快速排序(Quicksort). 先初步了解下Quicksort排序的概念(From Wikipedia). Quicksort is a divide and conquer algorithm. Quicksort first divides a large array into two smaller sub-arrays: the low elements and the high elements. Quicksort can ...
Filtered measures - filtered measures are visual level calculations with a specific filter applied (for example, Total Sales for France) and are used on some of the visuals created by the insights feature Categorical columns on X-axis unless it defines a sort by column that's scalar. If using...
This example is also interesting in that it has a NOSORT function. The group by does not need to sort because the index row source is already pre sorted. Views When a view cannot be merged into the main query you will often see a projection view operation. This indicates that the 'view...
wood-explain. Latest version: 40.5.607, last published: a year ago. Start using wood-explain in your project by running `npm i wood-explain`. There are 90 other projects in the npm registry using wood-explain.
With sonic toothbrushes, the entire brush head vibrates very quickly—and the manufacturers claim this produces a different type of cleaning action that makes them more effective. According to the marketing spiel, because a sonic toothbrush buzzes over your teeth at much higher speed than a normal...
Free Essay: Units help you better understand a problem because it gives you a basic understanding of what you're trying to solve. You can't just say "put two...
If you have a rotten wooden door or window, for example, you might chisel out the rot and replace it with epoxy resin filler, a very strong thermosetting plastic that will turn rock hard in a matter of minutes and stay that way for years. Car fenders are now mostly made of plastic—...
(s) with one degree or other of image-processing applied to their images to (for example) identify when a particularly nice sunset is happening with plenty of rose-tinted clouds. With enough foresight (and the right processing) it could pick up particularly aesthetic cloudscapes, the spontaneous...