• Wondertrader releases version v0.5.0


    Today (July 28, 2020), wondertrader released the latest version of v0.5.0, along with the latest version of wtpy, v0.5.0 Wondertrader has made the following changes in v0.5.0: High frequency strategy engine officially released。 High frequency strategy engine beforeWonderTraderHowever, due to insufficient testing, it has not been officially released for the time being. It only focuses […]

  • Deeply understand the implementation principle of transaction isolation level in MySQL


    preface When it comes to database transactions, it’s easy to get a lot of transaction related knowledge in your mind, such as the acid characteristics of transactions, isolation levels, and problems to be solved (dirty read, non repeatable read, phantom read), etc., but few people really know how these features of transactions are implemented and […]

  • [post] compatibility level of SQL Server


    Original post address:https://www.cnblogs.com/jinanxiaolaohu/p/10030021.html Alter database (transact SQL) compatibility level https://docs.microsoft.com/zh-cn/sql/t-sql/statements/alter-database-transact-sql-compatibility-level?view=sql-server-2017 Applicable objects:SQL Server (from 2008)Azure SQL databaseAzure SQL data warehouseParallel data warehouse Set some database behaviors to match the specifiedSQL server version is compatible.  For other alter database options, seeALTER DATABASE (Transact-SQL)。 For more information about syntax conventions, seeTransact SQL syntax conventions。 grammar copy ALTER […]

  • Layout of angular material (4): sub element alignment


    Child element alignment layout-alignThe command requires two values. The first value represents how the child elements are aligned horizontally in the layout, and the second value represents how the child elements are aligned vertically in the layout. When there is only one value in the instruction. For example,layout=”row” layout-align=”center”The element is centered horizontally and the […]

  • Django set default value to SQL


    Environment: Django 1.9.7 Background When Django migrate generates the table structure, default is not handled by default (that is, the default of the field is at the Django framework level, not at the database level). Of course, if you only use Django to do the project, but if the same library is operated by different […]

  • Spring 5 Chinese parsing core part – jsr330 standard annotation of IOC container


    1.11 use jsr330 standard annotation Starting with spring 3.0, spring provides support for jsr-330 standard annotations (dependency injection). These annotations are scanned in the same way as spring annotations. To use them, you need to rely on the relevant jar package in the classpath. If you use maven, javax.inject The components are in the standard […]

  • [mlflow series 4] mlflow upgrade cannot add foreign key constraint


    background staymlflow upgradeIn this article, we talked about the steps of mlflow upgrade. Fortunately, we did it in one go, and there were no mistakes,What I want to talk about today is how to handle the error of MySQL cannot add foreign key constraint during the upgrade processAmong them:Mlflow upgraded from 1.4.0 to 1.11.0MySQL version […]

  • InnoDB storage engine lock mechanism of MySQL


    1. Affairs 1.1 transaction overview Transactions are used to guarantee the integrity of the database — either all or none. Transactions must satisfy the four characteristics of acid. Atomicity means that the whole database transaction is an indivisible unit of work. Only if all database operations in the transaction are successful can the whole transaction […]

  • Twenty minutes package, the implementation of HTTP interaction between the front and back of an app


    In the process of react native development, almost all apps need to use HTTP requests, so the encapsulation of fetch is essential. Because the request parameters, parsing rules and token mechanism of different apps are completely different, in most app development, the implementation of HTTP requests in the front and back platforms is encapsulated by […]

  • Oracle SQL tree structure query


    The select statement in Oracle can use start with… Connect by prior clause to realize recursive query. Connect by is used in structured query, and its basic syntax is as follows: Copy codeThe code is as follows: select * from tablename start with cond1 connect by cond2 where cond3; In short, a tree structure is […]

  • 1.4 mastering the use of logging tools — Notes on the first line of Android code (Second Edition)


    The log tool class in Android is log( android.util.Log )The following five methods are provided in this class for us to print the log. Log. V(): used to print the most trivial and least significant log information. The corresponding level of verb is the lowest in Android logs. Log. D(): used to print some debugging […]

  • Take you to understand transform: rotate (including 3D view)


    preface Recently, in practice, we often need to use the CSS3 property transform: rotate, to X axis, Y axis, Z axisHow is it rotatedAfter struggling for a long time, I finally learned from my practice. I hope this article can help you. If you have any mistakes, please correct them, supplement them and exchange them […]