承接上一篇博客《GaussDB(DWS)性能调优系列基础篇一:万物之始analyze统计信息》,在GaussDB(DWS)的优化器根据analyze统计信息生成计划后,这里继续介绍如何详细解读计划以及计划的执行过程,从中发现可能存在的性能瓶颈点及其产生的原因。 前言 执行计划(又称解释计划)是数据库执行SQL语句的具体步骤,例如通过索引还是全表扫描...
The algorithm isn't simply returning the values that account for the biggest amount of the change. For example, if most (98%) sales came from the USA, then it would commonly be the case that most of the increase was also in the USA. Yet unless the USA or other countries/regions had...
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 ...
For example we may do a Full index scan when we do an unbounded scan of an index and want the data to be ordered in the index order. The optimizer may decide that selecting all the information from the index and not sorting is more efficient than doing a FTS or a Fast Full Index Sc...
The longest match number string dial-peer algorithm finds the dial-peer with the most numbers in a sequence that exactly match a sequence of numbers in a number string. This concept is clarified in the subsequent scenario. Scenario: Eligible dial-peers have been configured with t...
SortSelected rows were sorted using a sort algorithm. Union MergeThe results of multiple subselects were merged or combined into a single result. Subquery MergeThe results of multiple subselects were merged or combined into a single result. ...
1. What is the difference between the worse case and the best case running time of a merge sort? 2. True or false? Let Ai and Ai+1 be the ith largest and the (i+1) largest elements in A. Any algorithm E...
Seems to me, it simply means "has that playing position (i.e. the current state) been reached by pitting 'the algorithm' vs. any particular genuine chess-engine". (Or otherwise. The alternative, presumably, that it was a 'hand-crafted' response on Randall's part... Or possibly a volu...
If, for any reason, the algorithm of a large online platform favors one candidate, there is no way to counteract its impact, and if multiple online platforms all favor the same candidate, the impact of these dif- ferent sources of influence might be additive. Implications and Concerns ...
The "crypto nerd" (short for cryptography in this case, not cryptocurrency, which was only invented a few months before this comic) would be concerned with strongly encrypting data on their personal machine. This would conceivably come in handy when "villains" attempt to steal information on his...