b-tree

Sequentially Constructing Full B-Trees

由 倾然丶 夕夏残阳落幕 提交于 2020-01-24 13:06:21
问题 If I have a sorted set of data, which I want to store on disk in a way that is optimal for both reading sequentially and doing random lookups on, it seems that a B-Tree (or one of the variants is a good choice ... presuming this data-set does not all fit in RAM). The question is can a full B-Tree be constructed from a sorted set of data without doing any page splits? So that the sorted data can be written to disk sequentially. 回答1: Constructing a "B+ tree" to those specifications is simple.

Sequentially Constructing Full B-Trees

由 不问归期 提交于 2020-01-24 13:06:15
问题 If I have a sorted set of data, which I want to store on disk in a way that is optimal for both reading sequentially and doing random lookups on, it seems that a B-Tree (or one of the variants is a good choice ... presuming this data-set does not all fit in RAM). The question is can a full B-Tree be constructed from a sorted set of data without doing any page splits? So that the sorted data can be written to disk sequentially. 回答1: Constructing a "B+ tree" to those specifications is simple.

B-Tree 和 B+Tree 结构及应用，InnoDB 引擎， MyISAM 引擎

由 吃可爱长大的小学妹 提交于 2020-01-23 23:45:30
1.什么是B-Tree 和 B+Tree，他们是做什么用的？ B-Tree是为了磁盘或其它存储设备而设计的一种 多叉平衡查找树 ，B-Tree 和 B+Tree 广泛应用于文件存储系统以及数据库系统中。 在大规模数据存储中，实现索引查询这样一个实际背景下，树节点存储的元素数量是有限的（如果元素数量非常多的话，树的高度就会增大，查找就退化成节点内部的线性查找了），这样导致二叉查找树结构由于 树的深度过大而造成磁盘I/O读写过于频繁，进而导致查询效率低下 （为什么会出现这种情况？这跟外部存储器-磁盘的存储方式有关）。那么该如何减少树的高度呢？一个基本的想法就是：采用 多叉树 结构（每个节点存放多个元素，每个节点有多个子节点，这样树的高度就降低了）。根据平衡二叉树的启发，自然就想到平衡多路查找树结构。B-Tree的各种操作能使B-Tree保持较低的高度，从而达到有效避免磁盘过于频繁的查找存取操作，从而有效提高查找效率。 2.B-Tree 2.1定义 m阶B-Tree满足以下条件： 1、每个节点最多拥有m个子树 2、根节点至少有2个子树 3、分支节点至少拥有m/2颗子树（除根节点和叶子节点外都是分支节点） 4、所有叶子节点都在同一层 5、每个节点最多可以有m-1个key 6、每个节点中的key以升序排列 7、节点中key元素左节点的所有值都小于或等于该元素

TurboPower B-Tree Filer and Delphi XE2 - Anyone done it?

由 穿精又带淫゛_ 提交于 2020-01-05 07:27:47
问题 I might be the last guy on the planet relying on B-Tree Filer but I made the jump from Delphi 2007 to XE2. After getting over all the AnsiChar and PAnsiChar issues, the code now crashes with a Range Check with zero items on a page. Is anyone successfully running B-Tree Filer under Delphi XE2? If so, how'd ya do it? :) Update Range check error here: procedure IsamUnPack(var Page : IsamPage; KeyL : Word); var I, K, S : Word; P : Array [0..0] Of Byte absolute Page; {Real bounds [0..65535]} begin

TurboPower B-Tree Filer and Delphi XE2 - Anyone done it?

由 感情迁移 提交于 2020-01-05 07:27:11
问题 I might be the last guy on the planet relying on B-Tree Filer but I made the jump from Delphi 2007 to XE2. After getting over all the AnsiChar and PAnsiChar issues, the code now crashes with a Range Check with zero items on a page. Is anyone successfully running B-Tree Filer under Delphi XE2? If so, how'd ya do it? :) Update Range check error here: procedure IsamUnPack(var Page : IsamPage; KeyL : Word); var I, K, S : Word; P : Array [0..0] Of Byte absolute Page; {Real bounds [0..65535]} begin

MySQL when can I use HASH instead of BTREE

由 无人久伴 提交于 2020-01-02 04:05:21
问题 Since MySQL uses BTREE by default when creating an index, is there some instance when I can use HASH ? For example, if my table only consists of Foreign Keys which are just INT UNSIGNED values. Is it a good improvement to override BTREE with HASH in this case? Not sure if it matters, but I'm using InnoDB . 回答1: The HASH index type is only supported for MEMORY (aka HEAP ) storage engine. 来源： https://stackoverflow.com/questions/14418260/mysql-when-can-i-use-hash-instead-of-btree

MySQL when can I use HASH instead of BTREE

由 ╄→гoц情女王★ 提交于 2020-01-02 04:05:08
问题 Since MySQL uses BTREE by default when creating an index, is there some instance when I can use HASH ? For example, if my table only consists of Foreign Keys which are just INT UNSIGNED values. Is it a good improvement to override BTREE with HASH in this case? Not sure if it matters, but I'm using InnoDB . 回答1: The HASH index type is only supported for MEMORY (aka HEAP ) storage engine. 来源： https://stackoverflow.com/questions/14418260/mysql-when-can-i-use-hash-instead-of-btree

MySQL Hash Indexes for Optimization

由 感情迁移 提交于 2020-01-01 09:37:07
问题 So maybe this is noob, but I'm messing with a couple tables. I have TABLE A roughly 45,000 records I have TABLE B roughly 1.5 million records I have a query: update schema1.tablea a inner join ( SELECT DISTINCT ID, Lookup, IDpart1, IDpart2 FROM schema1.tableb WHERE IDpart1 is not NULL AND Lookup is not NULL ORDER BY ID,Lookup ) b Using(ID,Lookup) set a.Elg_IDpart1 = b.IDpart1, a.Elg_IDpart2 = b.IDpart2 where a.ID is NOT NULL AND a.Elg_IDpart1 is NULL So I am forcing the index on ID, Lookup.

B+树|MYSQL索引使用原则

由 早过忘川 提交于 2020-01-01 04:57:06
‘’MYSQL一直了解得都不多，之前写sql准备提交生产环境之前的时候，老员工帮我检查了下sql，让修改了一下存储引擎，当时我使用的是Myisam，后面改成InnoDB了。为什么要改成这样，之前都没有听过存储引擎，于是网上查了一下。 事实上使用不同的存储引擎也是有很大区别的，下面猿友们可以了解一下。 一、存储引擎的比较 注：上面提到的B树索引并没有指出是B-Tree和B+Tree索引，但是B-树和B+树的定义是有区别的。 在 MySQL 中，主要有四种类型的索引，分别为： B-Tree 索引， Hash 索引， Fulltext 索引和 R-Tree 索引。 B-Tree 索引是 MySQL 数据库中使用最为频繁的索引类型，除了 Archive 存储引擎之外的其他所有的存储引擎都支持 B-Tree 索引。Archive 引擎直到 MySQL 5.1 才支持索引，而且只支持索引单个 AUTO_INCREMENT 列。 不仅仅在 MySQL 中是如此，实际上在其他的很多数据库管理系统中B-Tree 索引也同样是作为最主要的索引类型，这主要是因为 B-Tree 索引的存储结构在数据库的数据检索中有非常优异的表现。 一般来说， MySQL 中的 B-Tree 索引的物理文件大多都是以 Balance Tree 的结构来存储的，也就是所有实际需要的数据都存放于 Tree 的 Leaf

Number of nodes in a B-Tree

由 落花浮王杯 提交于 2019-12-25 11:54:37
问题 How many nodes does a resulting B-Tree(min degree 2) have if I insert numbers from 1 to n in order? I tried inserting nodes from 1 to 20 there was a series for the number of nodes coming but i could not generalize it. Can anyone please help me derive the formula for this. 回答1: It will depend on the order of the B-Tree. The order of a BTree is the maximum number of children nodes a non-leaf node may hold (which is one more than the minimum number of keys such a node could hold). According to
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