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<div class="col-md-8 col-md-offset-2 opening-statement">
<div class="col-md-4">
<h3><a href="/2022/09/09/cmu15445-lab3/">cmu15445 project#3 - Query Execution</a></h3>
<span>
<span class="post-meta">
<time datetime="2022-09-09T08:18:46.350Z" itemprop="datePublished">
2022-09-09
</time>
</span>
</span>
</div>
<div class="col-md-8">
<p>
Project #3: Query Execution这部分实验要求为DBMS添加对查询执行的支持，根据给定的查询计划执行对应的查询操作
实验地址：https://15445.courses.cs.cmu.edu/fall2021/project3/
Task #1: Executors实验使用的处理模型是Iterator Model（也称Pipeline Model），查询计划中的每个操作符都提供了一个Next函数接口供上层操作符调用
</p>
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<a href="/2022/09/09/cmu15445-lab3/">Read More...</a>
</p>
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<div class="clearfix"></div>
<hr class="nogutter">
</div>
</div>
<div class="row">
<div class="col-md-8 col-md-offset-2 opening-statement">
<div class="col-md-4">
<h3><a href="/2022/09/09/cmu15445-lab4/">cmu15445 project#4 - Concurrency Control</a></h3>
<span>
<span class="post-meta">
<time datetime="2022-09-09T08:18:46.350Z" itemprop="datePublished">
2022-09-09
</time>
</span>
</span>
</div>
<div class="col-md-8">
<p>
Project #4: Concurrency Control这部分实验要求在DBMS中实现锁管理器LockManager以支持查询的并发执行，LockManager以元组作为数据共享的基本单位，事务对元组进行读写操作时需要根据隔离级别从LockManager处获取对应元组的共享锁或排他锁
实验地址：https://15445.courses.cs.cmu.edu/fall2021/project4/
Task #1: Lock Man
</p>
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<div class="col-md-8 col-md-offset-2 opening-statement">
<div class="col-md-4">
<h3><a href="/2022/09/09/cmu15445-lab1/">cmu15445 project#1 - Buffer Pool</a></h3>
<span>
<span class="post-meta">
<time datetime="2022-09-09T08:18:46.345Z" itemprop="datePublished">
2022-09-09
</time>
</span>
</span>
</div>
<div class="col-md-8">
<p>
Project #1: Buffer Pool这部分实验要求在存储管理器中实现一个buffer pool，用于在内存和磁盘间换入换出页面，从而允许DBMS提供给数据库远大于实际容量的内存空间。这里将磁盘中的块称作页面page，将内存中的块称作帧frame，buffer pool的换入换出操作对DBMS是透明的，DBMS向buffer pool请求指定page_id的页面，但并不知道页面是已缓存在内存中还是需要从磁盘读入
实验地址：htt
</p>
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<div class="col-md-8 col-md-offset-2 opening-statement">
<div class="col-md-4">
<h3><a href="/2022/09/09/cmu15445-lab2/">cmu15445 project#2 - Extendable Hash Index</a></h3>
<span>
<span class="post-meta">
<time datetime="2022-09-09T08:18:46.345Z" itemprop="datePublished">
2022-09-09
</time>
</span>
</span>
</div>
<div class="col-md-8">
<p>
Project #2: Extend-able Hash Index这部分实验要求为DBMS实现一个基于磁盘的可扩展哈希表，用于快速检索数据（个人理解是支持点查询）
实验地址：https://15445.courses.cs.cmu.edu/fall2021/project2/
Task #1: Page Layouts依赖于Project1的实现，哈希表需要通过DBMS的BufferPoolManager访问，即所有数据信息都必须保存
</p>
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<div class="col-md-8 col-md-offset-2 opening-statement">
<div class="col-md-4">
<h3><a href="/2022/09/09/cmu15445-lab0/">cmu15445 project#0 - C++ Primer</a></h3>
<span>
<span class="post-meta">
<time datetime="2022-09-09T08:18:46.332Z" itemprop="datePublished">
2022-09-09
</time>
</span>
</span>
</div>
<div class="col-md-8">
<p>
Project #0: C++ Primer这部分实验要求补充Matrix、RowMatrix和RowMaxtrixOperations三个类中对应函数的代码，RowMatrix类继承自Matrix类，表示一个二维矩阵；RowMatrixOperation类提供RowMatrix对象的矩阵加法和乘法运算
实验地址：https://15445.courses.cs.cmu.edu/fall2021/project0/
Matrix：
拷贝
</p>
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<div class="col-md-8 col-md-offset-2 opening-statement">
<div class="col-md-4">
<h3><a href="/2022/09/09/mit6.s081-lab10/">mit6.s081 lab10 - mmap</a></h3>
<span>
<span class="post-meta">
<time datetime="2022-09-09T07:51:27.921Z" itemprop="datePublished">
2022-09-09
</time>
</span>
</span>
</div>
<div class="col-md-8">
<p>
lab mmap这部分实验要求实现mmap和munmap系统调用，将完整或部分文件映射到内存空间中，从而通过内存地址相关指令来操纵文件，相较于read/write系统调用省去了在用户空间和内核空间来回切换的开销；并支持在移除映射时将脏数据写回磁盘
mmap函数定义如下，表示从文件描述符fd的addr+offset位置开始映射length字节到虚拟地址addr，并设置相应的访问权限和写回策略
1void *mmap(void *addr,
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<div class="col-md-8 col-md-offset-2 opening-statement">
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<h3><a href="/2022/09/09/mit6.s081-lab3/">mit6.s081 lab3 - pgtbl</a></h3>
<span>
<span class="post-meta">
<time datetime="2022-09-09T07:51:27.921Z" itemprop="datePublished">
2022-09-09
</time>
</span>
</span>
</div>
<div class="col-md-8">
<p>
lab pgtbl这部分实验主要关注页表page table，每个进程都有自己的页表，satp寄存器用于保存当前进程页表的物理地址，页表主要用于将虚拟地址转换为物理地址（实际上是MMU得到要转换的虚拟地址，通过CPU获取页表地址，查询页表得到对应的物理地址）
如果是一个虚拟地址对应页表中的一个表单项，那么64位的系统原则上会有2的64次方个地址，这会使得页表占用很大一部分内存并且难以管理，因此通常是以页面为单位，每个页面对应一个页表表项
</p>
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<div class="col-md-8 col-md-offset-2 opening-statement">
<div class="col-md-4">
<h3><a href="/2022/09/09/mit6.s081-lab7/">mit6.s081 lab7 - networking</a></h3>
<span>
<span class="post-meta">
<time datetime="2022-09-09T07:51:27.921Z" itemprop="datePublished">
2022-09-09
</time>
</span>
</span>
</div>
<div class="col-md-8">
<p>
lab networking这部分实验内容主要是实现网卡（E1000）驱动程序，完成数据包的发送和接收
E1000手册：8254x Family of Gigabit Ethernet Controllers Software Developer’s Manual (mit.edu)
一些相近的主机之间通过局域网相连，局域网能够容纳的主机数量是有限的，因此大型网络通常由多个独立的局域网组成，局域网之间通过路由器连接，路由器将来自一个局域
</p>
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<div class="col-md-8 col-md-offset-2 opening-statement">
<div class="col-md-4">
<h3><a href="/2022/09/09/mit6.s081-lab8/">mit6.s081 lab8 - lock</a></h3>
<span>
<span class="post-meta">
<time datetime="2022-09-09T07:51:27.921Z" itemprop="datePublished">
2022-09-09
</time>
</span>
</span>
</div>
<div class="col-md-8">
<p>
lab lock这部分实验要求对xv6内存分配器和块缓存进行锁优化，以提高在多核机器上的并行性
什么时候需要加锁？
一个简单而保守的回答是：如果两个进程访问了同一个数据结构，并涉及对这个数据结构的修改操作，那么就需要对这个数据结构加锁
加锁的两种实现方式：
使用coarse-grain lock，也就是全局锁，在访问某个数据结构的时候，对所有相关数据结构上锁，从而操作系统只能线性运行，失去了并发执行的能力
拆分锁，将其与数据结构和进程
</p>
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</div>
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<div class="col-md-8 col-md-offset-2 opening-statement">
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<h3><a href="/2022/09/09/mit6.s081-lab4/">mit6.s081 lab4 - traps</a></h3>
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<time datetime="2022-09-09T07:51:27.910Z" itemprop="datePublished">
2022-09-09
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lab trapslab4分为三个部分，第一部分是一些寄存器相关的基础问题，第二部分需要了解stack的相关用法实现backtrace，第三部分是通过time interrupt中断处理实现定期调用的功能，在这之前需要对xv6中的寄存器和栈stack有一定的了解
寄存器：
下图是xv6中的32个寄存器，汇编代码是在寄存器上执行而不是在内存中执行，因为寄存器是数据读取和运算的最快方式，在汇编代码中通过load指令将数据存放在寄存器中（这里
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