• Linux multithreading: mutex, conditional variable, read-write lock, spin lock, semaphore


    1、 Mutex (synchronous) In a multitasking operating system, multiple tasks running at the same time may need to use the same resource. This process is a bit similar to that in the company department, while I am using the printer to print things (I haven’t finished printing), others are also using the printer to print […]

  • Mongo basic operation


    ======Install document===== https://docs.mongodb.com/manual/installation/ Crud operation of database DB display the current database, the default is test Show DBS lists the available databases Show tables, show collections lists the available collections in the database Use < Database > is used to switch databases =====View database show dbs =====Switch rocketchat database use rocketchat =====View database集合 show tables,show […]

  • Flag pager_ Non analysis of pages


    Database information: Code program: if __name__ == “__main__”: user=User.query.paginate(1,2) for i in user.iter_pages(): print(i,end=” “) Output information: 1 2 3 4 5 none 8 9 Today, I have a look at the source code to analyze it def iter_pages(self, left_edge=2, left_current=2, right_current=5, right_edge=2): last = 0 for num in xrange(1, self.pages + 1): if num […]

  • [20201126] 11g VPD problem.txt


    [20201126] 11g VPD problem.txt –//Links https://hourim.wordpress.com/2020/09/30/ddl-optimization-and-vpd/ The problems mentioned in the test environment test look.–//You can check the Chinese version for a more detailed description of the changes in the operation mode of adding columns in 10g, 11g and 12C–//https://www.oracle.com/technetwork/cn/articles/database/ddl-optimizaton-in-odb12c-2331068-zhs.html–//I only tested 11g environments. 1. Environment:[email protected]> @ ver1PORT_STRING                    VERSION        BANNER—————————— ————– ——————————————————————————–x86_64/Linux 2.4.xx       Oracle […]

  • A case of SQL optimization: or condition optimization


    This paper is compiled from:Kangaroo cloud technology | SQL optimization case ( two ) : or condition optimization Data stack is a cloud native station data center PAAS. We have an interesting open source project on GitHub:https://github.com/DTStack/flinkx Flinkx is a Flink based batch flow unified data synchronization tool, which can collect both static data, such […]

  • Relearning front end JavaScript (2) JavaScript statements


    This article mainly introduces the statements in JavaScript, including several loop statements and conditional statements. Conditional statements in JavaScript 1、 Definition  Conditional statementWhen the condition is satisfied, execute a statement2Conditional statements in JavaScript  1) if…else if … else: when the specified condition is true, the if statement will execute a section of statement. If the condition of […]

  • Mongoose data query or, and, where usage


    or by$orThe condition specifies the parameters; //member = [“zhangsan”, “lisi”, “wangwu”]; let filter = { $or: [ {docKey: “public”}, {owner: “zhangsan”}, {member: “lisi”} ] } db.getCollection(‘docs’).find(filter); Data filtering or yes or query If one of the following conditions is met, the relevant data can be found If the database parameter is an array, it will […]

  • Django uses or conditional queries and various query keywords


    Django uses or condition query: from django.db.models import Q User.objects.filter(Q(state=0) | Q(state=1)) Django query keywords: __ Exact equals like ‘AAA’__ Iexact is exactly the same as ignore case like ‘AAA’__ Contains contains like% AAA%__ Icontains contains ignore case like ‘% AAA%’, but for SQLite, the effect of contains is equivalent to icontains.__ GT greater than__ […]

  • Bayesian simple linear regression simulation analysis of R language Gibbs sampling


    Link to the original text:http://tecdat.cn/?p=4612 Many introductions of Bayesian analysis use relatively simple teaching examples (for example, the inference of success probability based on Bernoulli data). Although this is a good introduction to Bayesian principles, it is not direct to extend these principles to regression. This article will outline how these principles can be extended […]

  • Mybatis dynamic mapping, this time I finally got it


    Focus on “Java back end technology stack” Reply to “interview” for full interview information Dynamic SQL is one of the powerful features of mybatis. If you have used JDBC or other similar frameworks, you should be able to understand how painful it is to splice SQL statements according to different conditions. For example, when splicing, […]

  • Database mysql needs to learn basic knowledge


    MySQL as the current mainstream of relational database management system, it is no exaggeration to say that every programmer must master the basic skills. So, what basic knowledge does MySQL database need to learn? First of all, you need to know mysql, understand the operation of database and table, learn where conditional query and MySQL […]

  • SQL query of data scientist


    Author | soner y ı LD ı R ı MCompile VKSource: towards Data Science SQL is a programming language, which is used by most RDBMS to manage data stored in tabular form. SQL is a basic skill expected by data scientists. You might say that this is the job of a data engineer, but the […]