smartclient | 易学教程

数据库中间件漫谈——看看云时代，它会走向何方

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1.前言随着业务的发展，MySQL数据库中的表会越来越多，表中的数据量也会越来越大，相应地，数据操作的开销也会越来越大；另外，无论怎样升级硬件资源，单台服务器的资源（CPU、磁盘、内存、网络IO、事务数、连接数）总是有限的，最终数据库所能承载的数据量、数据处理能力都将遭遇瓶颈。分表、分库和读写分离可以有效地减小单台数据库的压力。而数据库中间件，也火了很长一段时间，基本上每个大厂都会自研一套。本文主要针对业界主流的数据库中间件的实现、功能、成本等方面进行对比，总结数据库中间件的实现方式，并展望未来的可能发展。实现方式一般来说，对于数据库中间件，可以在以下六个层次做切入。 2.1 代码层在同一个项目中创建多个数据源，采用if else的方式，直接根据条件在代码中路由。 Spring中有动态切换数据源的抽象类，具体参见AbstractRoutingDataSource。如果项目不是很庞大，使用这种方式能够快速的进行分库。但缺点也是显而易见的，这种海量的代码侵入是绝不能被接受的。而且当查询结果返回时，需要对跨库、聚合等查询结果进行归并，开发工作量非常巨大。这种方式了解一下即可，一般不会去使用。 2.2 框架层主要是修改或增强现有ORM框架的功能，在SQL中增加一些自定义原语或者hint来实现。常见的比如实现一些拦截器（比如Mybatis的Interceptor接口）

三点须知：当我们在开发过程中需要用到分布式缓存Redis的时候

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当我们在开发过程中需要用到分布式缓存Redis 的时候，我们首先要明白缓存在系统中用来做什么？ 1. 少量数据存储，高速读写访问。通过数据全部in-momery 的方式来保证高速访问，同时提供数据落地的功能，实际这正是Redis最主要的适用场景。 2. 海量数据存储，分布式系统支持，数据一致性保证，方便的集群节点添加/删除。Redis3.0以后开始支持集群，实现了半自动化的数据分片，不过需要smart-client的支持。华为云分布式缓存Redis ，目前已经进入 Redis5.0 公测阶段，公测阶段注册既能免费使用，那么我们在开发过程中需要用到Redisde 时候，需要明白哪些问题呢？下面小编给大家一一道来。一、为什么使用 Redis？我觉得在项目中使用 Redis，主要是从两个角度去考虑：性能和并发。当然，Redis 还具备可以做分布式锁等其他功能，但是如果只是为了分布式锁这些其他功能，完全还有其他中间件，如 ZooKpeer 等代替，并不是非要使用 Redis。因此，这个问题主要从性能和并发两个角度去答。性能：如下图所示，我们在碰到需要执行耗时特别久，且结果不频繁变动的 SQL，就特别适合将运行结果放入缓存。这样，后面的请求就去缓存中读取，使得请求能够迅速响应。题外话：忽然想聊一下这个迅速响应的标准。根据交互效果的不同，这个响应时间没有固定标准。

Is smartclient suitable?

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问题 How does the waiting time for SmartClient scale across thousands of users editing grids? I have received warnings before that ExtJS would not be suitable. 回答1: SmartClient has a single grid component that does both horizontal and vertical incremental rendering, so it handles a very very large number of both rows (several million) and columns (several hundred) without degradation in performance. All of the grid features supported by SmartClient - inline editing, grouping, filtering, dynamic

SmartClient: How to use modal window

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问题 I want to develop an application in SmartClient using javascript. In that application, it takes inputs like price range and category. On form submit, without reloading the page it will send request to server and will get the list of items.few of them will be displayed after submit(on step 2) and other will be displayed on 3rd step. And there will be a database query fired after step-2 and step-3 Structure to display items details contains item_pic, Item_name, item_price and availability. How

SmartClient: How to use modal window

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ExtJS or SmartClient?

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问题 I would like your opinion about these two frameworks. I like a lot the features of ExtJS, but recently I saw SmartClient and it seems to be great too, and free (its Client side features) for commercial projects. I tried a little of SmartClient and it seems to be easier than ExtJS, and it has a better documentation tnan ExtJS. BUT.. I didn't work with any of these frameworks and maybe I'm wrong. That's why I would like the opinion of people who has worked with them. And BTW.. how does the

How to apply style on StaticTextItem component of DynamicForm in SmartGWT?

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问题 I want to apply style on StaticTextItem in SmartGWT's DynamicForm item. I did not find any method like setStyleName for this component. Is there any alternate way to apply style on StaticTextItem? I have also noticed that ToolStrip Component can add only Form items, So Here I am stuck how would I apply a style particularly on StaticTextItem. My goal is just add label with style on ToolStrip. Any alternative to this appreciated!!! Thanks!!! 回答1: You can use following properties to apply styles

.NET ClickOnce deployment and wrong assemblies called after updated version

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问题 I have a ClickOnce application (app1) that calls DLL files from another solution (app2). I recently updated this application at one customer and a strange thing occurred. He got the new version (publish version was correct in Control Panel / Add or Remove Programs ) of app1 and the application version was correct as manually inspected in the application. But the DLL files called from the referenced solution (app2) was still the old ones. We deleted all files in C:\Documents and Settings

.NET - ClickOnce Install - Company Name and Application Name

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问题 What is the proper way to set the Company Name and Application Name in a ClickOnce application? I have a set of projects in a solution called RecordNavigator. The GUI project is called RecordNavigator.Gui. When I publish the application - I want the Start menu to have a folder called Tyndall Software and the application shortcut to be called Record Navigator . Right now the folder says Organization and the shortcut says RecordNavigator.Gui . The AssemblyInfo.cs file seems to have no effect.

ExtJS or SmartClient?

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I would like your opinion about these two frameworks. I like a lot the features of ExtJS, but recently I saw SmartClient and it seems to be great too, and free (its Client side features) for commercial projects. I tried a little of SmartClient and it seems to be easier than ExtJS, and it has a better documentation tnan ExtJS. BUT.. I didn't work with any of these frameworks and maybe I'm wrong. That's why I would like the opinion of people who has worked with them. And BTW.. how does the license of ExtJS work? you've to but one license for each developer and then you're able to develop and

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