computer-science

问题 Are MySQL operations multithreaded? Specifically, on running a select, does the select (or join) algorithm spawn multiple threads to run together? Would being multi-threaded prevent being able to support a lot of concurrent users? 回答1: Several background threads run in a MySQL server. Also, each database connection is served by a single thread. Parallel queries (selects using multiple threads) are not implemented in MySQL. MySQL as is can support "a lot of concurrent useres". For example

问题 I am refreshing on algorithm theory (from Cormen). There is an exercise in the chapter for binary tries that asks: Can the min-heap property be used to print out the keys of an n-node tree in sorted order in O(n) time? Show how, or explain why not. I thought yes it is possible. In the min heap the element in a node is smaller than both its children. So the root of the heap is always the smaller element of all the n elements and the left child of the root is the smaller than all the elements

问题 Since version 3.0, DenseFeatureDetector is no longer available. Could anybody please show me how to compute Dense SIFT features in OpenCV 3.0? I couldn't find it in the documentation. Thank you very much in advance! 回答1: Here's how I used dense SIFT in OpenCV 3 C++: SiftDescriptorExtractor sift; vector<KeyPoint> keypoints; // keypoint storage Mat descriptors; // descriptor storage // manual keypoint grid int step = 10; // 10 pixels spacing between kp's for (int y=step; y<img.rows-step; y+

问题 Suppose I have two arrays and I want to merge them so that the merged array has the minimum amount of repetitions . For example [ 'x', 'x' ] is a repetition. arr1 = [ 'x', 'd', 'd', 'm', 'f', 'm' ] arr2 = [ 'd', 'd', 'x', 'f', 'f', 'm' ] The only condition is that in the merged array, the elements from arr1 and arr2 must appear in their respective orders within arr1 and arr2 . Below is an example of the merged array with 0 repetitions while maintaining this condition. merged = [ 'd', 'x', 'd'

问题 This is a question just for the sake of asking: Barring all intermediate to advanced topics or techniques (clustered indices, BULK INSERTS, export/import tricks, etc.), does an INSERT take longer the larger a table grows? This assumes that there is only one auto-int column, ID [i.e., all new rows are INSERTED at the bottom, where no memory has to shuffled to accommodate a specific row positioning]. A link to a good "benchmarking MySQL" would be handy. I took Oracle in school, and so far the

问题 Specifically a Multigraph. Some colleague suggested this and I'm completely baffled. Any insights on this? 回答1: It's pretty straightforward to store a graph in a database: you have a table for nodes, and a table for edges, which acts as a many-to-many relationship table between the nodes table and itself. Like this: create table node ( id integer primary key ); create table edge ( start_id integer references node, end_id integer references node, primary key (start_id, end_id) ); However,

问题 We have two lists, let's say students and their scores. I want to compare these two lists and find the delta between the new list and the old list, then find the least intrusive way to Insert or Update into the new list any changes. What is the best algorithm to approach this? Want to focus on minimal amount of changes to new list and performance. Example code: List<ListItem> existingList = new List<ListItem>(); List<ListItem> newList = new List<ListItem>(); public TopLists() { InitTwoLists()

问题 It occurred to me today that although I've adopted and don't infrequently use the term "semantics" when referring to language elements and naming conventions, I don't have any sense of a formal definition. My attempt to find a formal definition in the programming domain made my eyes glaze over. I have a sense of its meaning from the contexts in which I've encountered it, and from its more common usage with respect to linguistics, and I typically use the term to refer to the meaning or

问题 I've been reading things here and there for a while now about using an "ant colony" model as a heuristic approach to optimizing various types of algorithms. However, I have yet to find an article or book that discusses ant colony optimizations in an introductory manner, or even in a lot of detail. Can anyone point me at some resources where I can learn more about this idea? 回答1: On the off chance that you know German (yes, sorry …), a friend and I have written an introduction with code about

问题 I've been working through a recent Computer Science homework involving recursion and big-O notation. I believe I understand this pretty well (certainly not perfectly, though!) But there is one question in particular that is giving me the most problems. The odd thing is that by looking it, it looks to be the most simple one on the homework. Provide the best rate of growth using the big-Oh notation for the solution to the following recurrence? T(1) = 2 T(n) = 2T(n - 1) + 1 for n>1 And the