May 2024
Intermediate to advanced
347 pages
5h 38m
Chinese
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第11章 Java大数据分析
“在拓荒时代，人们使用牛来牵拉重物，而如果一头牛拉不动圆木，人们并不会通过养一头更大的牛来解决这个问题。同样的，我们不应该通过更大的计算机来解决复杂的问题，而应该通过使用更多的计算机系统来解决问题。”
——Grace Hopper (1906—1992)
大数据这个术语通常指存储、检索以及分析大量数据集使用的算法，这些数据集太大，不能通过单个文件服务器管理。在商业上，这些算法是由Google首创的，本章也会考察它们的两个早期基准算法：PageRank和MapReduce。
在20世纪30年代，美国数学家爱德华•卡斯纳（Edward Kasner）的九岁侄子创造了单词“googol”，这个词表示10100。在那个年代，宇宙中的粒子数目据估计大约是1080。此后，Kasner又创造了一个新词汇“googolplex”，用来代表10google。这个数字可以写成1后面跟着10100个零。谷歌在加利福尼亚山景的总部就叫Googleplex。
11.1 扩展、数据分块和分片
关系数据库（Rdb）不擅长超大型数据库的管理。我们在第10章“NoSQL数据库”中看到过，这也是开发NoSQL数据库的一个主要原因。
一般来说，有两种方法来管理不断增长的大型数据集：垂直扩展和水平扩展。垂直扩展指的是增加单个服务器容量的策略，手段是升级到更有力的CPU，更多的主存储器以及更多的存储空间。水平扩展指的是通过增加系统中的服务器的数量来重新分配数据集。垂直扩展的优点是，它不需要对现有的软件进行任何明显更新，主要的缺点是比水平扩展更严格。水平扩展的主要问题是它确实要求软件上的调整。但是如我们所见，像MapReduce这样的框架使许多调整易于管理。 ...
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