MSSQL一直以来被人们认为简单、好学,但等到大家掌握了入门操作,深入理解起来又觉得非常的“拧巴”,尤其是对用惯了Oracle的同学来说,究其根本原因,无非是MSSQL引入和暴露了太多的概念、细节和理论层,而Oracle恰恰屏蔽了这些,比如下面讲到的这些概念,即使是使用很久MSSQL的同学来说,也未必就真理解的正确,下面这段文字,很好的解释了MSSQL中的几个基本概念:

Scheduler (SOS Scheduler)– the object that manages thread scheduling in SQL Server and allows threads to be exposed to the CPU (described in sys.dm_os_schedulers). This is the all-powerful but benign and graceful master whom everyone abides.  He does not control things but lets the workers work with each other and relies on their cooperation (co-operative scheduling mode). Each scheduler /master (one per logical CPU) accepts new tasks and hands them off to workers. SOS Scheduler allows one worker at a time to be exposed to the CPU.

Task –a task represents the work that needs to be performed (sys.dm_os_tasks). A task contains one of the following requests: query request (RPC event or Language event), a prelogin request (prelogin event),  a login request (connect event), a logout request (disconnect event), a query cancellation request (an Attention event), a bulk load request (bulk load event), a distributed transaction request (transaction manager event). A task is what the Master is about – it is what defines its existence. Note these are tracked at the SOS scheduler layer (thus dm_OS_tasks)

Worker (worker thread) – This is the logical SQL Server representation of a thread (think of it as a wrapper on top of the OS thread). It is a structure within the Scheduler which maintains SQL Server-specific information about what a worker thread does. sys.dm_os_workers. Workers are the humble servants who carry out the task assigned to them by the Master (scheduler).

Thread – this is the OS thread sys.dm_os_threads that is created via calls like CreateThread()/_beginthreadex(). A Worker is mapped 1-to-1 to a Thread.

Request is the logical representation of a query request made from the client application to SQL Server (sys.dm_exec_requests). This query request has been assigned to a task that the scheduler hands off to a worker to process. This represents query requests as well as system thread operations (like checkpoint, log writer, etc); you will not find login, logouts, attentions and the like here. Also, note that this is a representation at the SQL execution engine level (thus dm_EXEC_requests) not at the SOS Scheduler layer.

Sessions – when the client application connects to SQL Server the two sides establish a "session" on which to exchange information. Strictly speaking a session is not the same as the underlying physical connection, it is a SQL Server logical representation of a connection. But for practical purposes, you can think of this as being a connection (session =~ connection). See sys.dm_exec_sessions. This is the old SPID that existed in SQL Server 2000 and earlier. You may sometimes notice a single session repeating multiple times in a DMV output. This happens because of parallel queries. A parallel query uses the same session to communicate with the client, but on the SQL Server side multiple worker (threads) are assigned to service this request. So if you see multiple rows with the same session ID, know that the query request is being serviced by multiple threads.

Connections – this is the actual physical connection established at the lower protocol level with all of its characteristics sys.dm_exec_connections . There is a 1:1 mapping between a Session and a Connection.tr

Scheduler & Task & Worker & Thread & Request & Session & Connection of SQL Server的更多相关文章

  1. 【总算解决了】A network-related or instance-specific error occurred while establishing a connection to SQL Server

    给别人做的网站莫名其妙连接不上数据库.百度了好多,总算知道自己的错在哪了. 报 "A network-related or instance-specific error occurred  ...

  2. 【SQL Server 问题记录】A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible.

    本文涉及的相关问题,如果你的问题或需求有与下面所述相似之处,请阅读本文 A network-related or instance-specific error occurred while esta ...

  3. idea Connection to SQL Server - 公网8 failed java

    Connection to SQL Server - 公网8 failed java.sql.SQLException: I/O Error: SSO Failed: Native SSPI libr ...

  4. A network-related or instance-specific error occurred while establishing a connection to SQL Server

    今天同事给我发了个图片过来,  服务器环境 sql 2000 + IIS7 看到这张图片,我先自己试了下,确实是有这个问题的,而且不是偶然性的,那么再看报错意思,在跟sql建立连接的时候发生了一个错误 ...

  5. Tosca Connection Validation error:40 - Could not open a connection to SQL Server (不知道怎么解决)

    谁知道下面这个错怎么解决,请给我留言,谢谢. 数据库能正常链接,服务也是 normal running

  6. Do waiting or suspended tasks tie up a worker thread?

      https://blogs.msdn.microsoft.com/askjay/2012/07/29/do-waiting-or-suspended-tasks-tie-up-a-worker-t ...

  7. WPF数据库连接错误:The user is not associated with a trusted SQL Server connection.

    我当初安装sql server的时候选的Window Authentication mode,没选SQL Server Windows Authentication. 后来做WPF时连接数据库时需要一 ...

  8. Exception thrown on Scheduler.Worker thread. Add `onError` handling

    <html> <head></head> <body> java.lang.IllegalStateException: Exception throw ...

  9. MS SQL错误:SQL Server failed with error code 0xc0000000 to spawn a thread to process a new login or connection. Check the SQL Server error log and the Windows event logs for information about possible related problems

          早晨宁波那边的IT人员打电话告知数据库无法访问了.其实我在早晨也发现Ignite监控下的宁波的数据库服务器出现了异常,但是当时正在检查查看其它服务器发过来的各类邮件,还没等到我去确认具体情 ...

随机推荐

  1. CentOS6.5下安装配置MySQL数据库

    一.MySQL简介 说到数据库,我们大多想到的是关系型数据库,比如MySQL.Oracle.SQLServer等等,这些数据库软件在Windows上安装都非常的方便,在Linux上如果要安装数据库,咱 ...

  2. redhat 配置yum源(配置163 yum repo)

    一般安装好redhat后,不能注册的话,不能使用系统自带的yum源.但是我们可以自己配置yum源来解决这一问题.下面介绍下redhat配置163yum源. 1) 查看版本号和系统类别: cat /et ...

  3. VS2010_慢

    ZC:IntelliSense 一旦关闭,代码提示 也就没有了... ZC:IntelliSense 和 IntelliTrace,不是一个东西... 1.http://blog.csdn.net/c ...

  4. JNI手动释放内存(避免内存泄露)

    . 哪些需要手动释放? 不要手动释放(基本类型): jint , jlong , jchar 需要手动释放(引用类型,数组家族): jstring,jobject ,jobjectArray,jint ...

  5. QT---事件系统

    1         QT事件系统 1.1  事件的定义 QT中事件是有专门的类QEvent,常见的有键盘事件QKeyEvent.鼠标事件QMouseEvent和定时器事件QTimerEvent.例如用 ...

  6. Asp.net core 学习笔记 ( Web Api )

    asp.net core 把之前的 webapi 和 mvc 做了结合. mvc 既是 api. 但是后呢,又发现, api 确实有独到之处,所以又开了一些补助的方法. namespace Proje ...

  7. (转)c#反射

    1. 什么是反射2. 命名空间与装配件的关系3. 运行期得到类型信息有什么用4. 如何使用反射获取类型5. 如何根据类型来动态创建对象6. 如何获取方法以及动态调用方法7. 动态创建委托 1.什么是反 ...

  8. 用ActionController::Renderer的render方法渲染模版

    使用Cable进行pub: ActionCable.server.broadcast "call", {address: AddressesController.render(@a ...

  9. vue select的change事件,将点击过的城市名存在数组中,下次调用不需要再调用接口

    <template> <div id="body" class="application" v-show="show" v ...

  10. vux 给元素动态添加css

    <template> <div class="jdtI" :style="{styleObj}"></div> </t ...