Extendible Hashing (Dynamic approach to DBMS)
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Extendible Hashing (Dynamic approach to DBMS)
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原文
缩写
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eg. = exempli gratia 比如
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viz. = 即，也就是
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w.r.t = 关于(with respect to)
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aka = also know as 也称为
译文
Extendible Hashing is a dynamic hashing method wherein directories, and buckets are used to hash data. It is an aggressively flexible method in which the hash function also experiences dynamic changes.
Extendible Hashing 是一种动态哈希方法，其中目录和桶被用于哈希数据。可扩展哈希是一个有力的灵活的方法，其中哈希函数也经历动态的改变。
Main features of Extendible Hashing: The main features in this hashing technique are:
Main features of Extendible Hashing: 在哈希技术中主要的特征如下：
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Directories: The directories store addresses of the buckets in pointers. An id is assigned to each directory which may change each time when Directory Expansion takes place.
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目录: 目录在指针中存储桶的地址。每个目录被分配一个id ，每次目录扩张时，id可能会发生变化。
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Buckets: The buckets are used to hash the actual data.
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桶: 桶被用于哈希真实的数据。
Basic Structure of Extendible Hashing:
可扩展哈希的基本结构
Frequently used terms in Extendible Hashing:
在可扩展哈希中常用术语
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Directories: These containers store pointers to buckets. Each directory is given a unique id which may change each time when expansion takes place. The hash function returns this directory id which is used to navigate to the appropriate bucket. Number of Directories = 2^Global Depth.
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目录: 这个容器存储指向桶的指针。每个目录给定一个唯一的id，当扩张发生时id可能随之改变。哈希函数返回这个目录的id，这个id被用来指向合适的桶。
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Buckets: They store the hashed keys. Directories point to buckets. A bucket may contain more than one pointers to it if its local depth is less than the global depth.
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桶: 它们存储哈希键。目录指向桶。如果局部深度小于全局深度时，一个桶可能包含不止一个指针指向它。
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Global Depth: It is associated with the Directories. They denote the number of bits which are used by the hash function to categorize the keys. Global Depth = Number of bits in directory id.
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全局深度：它跟目录相关联。它们表示哈希函数使用的比特位数目去分类这些键。全局深度=目录id的比特位数。
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Local Depth: It is the same as that of Global Depth except for the fact that Local Depth is associated with the buckets and not the directories. Local depth in accordance with the global depth is used to decide the action that to be performed in case an overflow occurs. Local Depth is always less than or equal to the Global Depth.
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局部深度：和全局深度类似，除了局部深度是跟桶关联，而不是跟目录。当桶溢出发生时，局部深度根据全局深度去决定执行的行为。局部深度通常小于等于全局深度。
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Bucket Splitting: When the number of elements in a bucket exceeds a particular size, then the bucket is split into two parts.
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桶分裂：当桶的元素超过了特定的大小，那么桶分裂成两个部分。