DBLE 与 MyCat 对应分片算法名和异同

第七种 DBLE分片算法—jumpStringHash

除了以上六种常见的分片算法之外，DBLE 还独有一种分片算法：跳跃字符串算法。

具体配置如下：

#rule.xml<function name="jumphash"          class="jumpStringHash">        <property name="partitionCount">2</property>        <property name="hashSlice">0:2</property></function>

partitionCont：分片数量

hashSlice：分片截取长度

该算法来自于 Google 的一篇文章《A Fast, Minimal Memory, Consistent Hash Algorithm》其核心思想是通过概率分布的方法将一个hash值在每个节点分布的概率变成1/n，并且可以通过更简便的方法可以计算得出，而且分布也更加均匀。

注意事项：分片字段值为NULL时，数据恒落在0号节点之上;当真实存在于mysql的字段值为not null的时候,报错 "Sharding column can't be null when the table in MySQL column is not null"

至此，我们DBLE中支持的七种分片算法就介绍完了，相信读者朋友对 DBLE 的使用也慢慢熟悉。

系列文章的最后：

完整分区实例

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE dble:rule SYSTEM "rule.dtd"><dble:rule xmlns:dble="; version="9.9.9.9">    <tableRule name="sharding-by-enum">        <rule>            <columns>id</columns>            <algorithm>enum</algorithm>        </rule>    </tableRule>    <tableRule name="sharding-by-range">        <rule>            <columns>id</columns>            <algorithm>rangeLong</algorithm>        </rule>    </tableRule>    <tableRule name="sharding-by-hash">        <rule>            <columns>id</columns>            <algorithm>hashLong</algorithm>        </rule>    </tableRule>    <tableRule name="sharding-by-hash2">        <rule>            <columns>id</columns>            <algorithm>hashLong2</algorithm>        </rule>    </tableRule>    <tableRule name="sharding-by-hash3">        <rule>            <columns>id</columns>            <algorithm>hashLong3</algorithm>        </rule>    </tableRule>    <tableRule name="sharding-by-mod">        <rule>            <columns>id</columns>            <algorithm>hashmod</algorithm>        </rule>    </tableRule>    <tableRule name="sharding-by-hash-str">        <rule>            <columns>id</columns>            <algorithm>hashString</algorithm>        </rule>    </tableRule>    <tableRule name="sharding-by-date">        <rule>            <columns>calldate</columns>            <algorithm>partbydate</algorithm>        </rule>    </tableRule>    <tableRule name="sharding-by-pattern">        <rule>            <columns>id</columns>            <algorithm>pattern</algorithm>        </rule>    </tableRule>    <!-- enum partition -->    <function name="enum"              class="Enum">        <property name="mapFile">partition-hash-int.txt</property>        <property name="defaultNode">0</property><!--the default is -1,means unexpected value will report error-->        <property name="type">0</property><!--0 means key is a number, 1 means key is a string-->    </function>    <!-- number range partition -->    <function name="rangeLong" class="NumberRange">        <property name="mapFile">autopartition-long.txt</property>        <property name="defaultNode">0</property><!--he default is -1,means unexpected value will report error-->    </function>    <!-- Hash partition,when partitionLength=1, it is a mod partition-->    <!--MAX(sum(count*length[i]) must not more then 2880-->    <function name="hashLong" class="Hash">        <property name="partitionCount">8</property>        <property name="partitionLength">128</property>        <!-- <property name="partitionCount">2,3</property>        <property name="partitionLength">4,5</property>-->    </function>    <!-- Hash partition,when partitionLength=1, it is a mod partition-->    <!--MAX(sum(count*length[i]) must not more then 2880-->    <function name="hashLong2" class="Hash">        <property name="partitionCount">2</property>        <property name="partitionLength">512</property>        <!-- <property name="partitionCount">2,3</property>        <property name="partitionLength">4,5</property>-->    </function>    <!-- Hash partition,when partitionLength=1, it is a mod partition-->    <!--MAX(sum(count*length[i]) must not more then 2880-->    <function name="hashLong3" class="Hash">        <property name="partitionCount">2,1</property>        <property name="partitionLength">256,512</property>        <!-- <property name="partitionCount">2,3</property>        <property name="partitionLength">4,5</property>-->    </function>    <!-- eg:  mod 4 -->    <function name="hashmod" class="Hash">        <property name="partitionCount">4</property>        <property name="partitionLength">1</property>    </function>    <!-- Hash partition for string-->    <function name="hashString" class="StringHash">        <property name="partitionCount">8</property>        <property name="partitionLength">128</property>        <property name="hashSlice">0:2</property>        <!--<property name="hashSlice">-4:0</property> -->    </function>    <!-- date partition -->    <!-- 4 case:    1.set sEndDate and defaultNode: input <sBeginDate ,router to defaultNode; input>sEndDate ,mod the period    2.set sEndDate, but no defaultNode:input <sBeginDate report error; input>sEndDate ,mod the period    3.set defaultNode without sEndDate: input <sBeginDate router to defaultNode;input>sBeginDate + (node size)*sPartionDay-1 will report error(expected is defaultNode,but can't control now)    4.sEndDate and defaultNode are all not set: input <sBeginDate report error;input>sBeginDate + (node size)*sPartionDay-1 will report error     -->    <function name="partbydate" class="Date">        <property name="dateFormat">yyyy-MM-dd</property>        <property name="sBeginDate">2015-01-01</property>        <property name="sEndDate">2015-01-31        </property> <!--if not set sEndDate,then in fact ,the sEndDate = sBeginDate+ (node size)*sPartionDay-1 -->        <property name="sPartionDay">10</property>        <property name="defaultNode">0</property><!--the default is -1-->    </function>    <!-- pattern partition -->    <!--mapFile must contains all value of 0~patternValue-1,key and value must be Continuous increase-->    <function name="pattern"              class="PatternRange">        <property name="mapFile">partition-pattern.txt</property>        <property name="patternValue">1024</property>        <property name="defaultNode">0</property><!--contains string which is not number,router to default node-->    </function></dble:rule>

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