此文已由作者张镐薪授权网易云社区发布。

欢迎访问网易云社区，了解更多网易技术产品运营经验。

意思就是，开头为北京的范围在A0000000~A9999999的根据后面的哈希值对5取模平均分布在0，1，2,3,4分片节点上。开头为北京的范围在B0000000以上的根据后面的哈希值对5取模平均分布在5,6,7,8,9分片节点上。开头为上海的范围在00000000~10000000的根据后面的哈希值对2取模平均分布在10,11分片节点上，剩下的开头为上海的，对6取模平均分布在10,11，12,13,14,15上。  这样，在发现某个开头的分片不够用时，可以随时改变分片规则，只要不删除之前的分片规则，就不影响以前数据的访问。在完成数据迁移后，可以删除之前的规则。 实现方法就是采用hashmap存储这些对应关系：

/**
* 首先实现不带范围约定的复合规则，即配置文件中为：
* 北京=0，1，2,3,4
* 上海=10,11
*/public class PartitionByRouteHash extends AbstractPartitionAlgorithm implements RuleAlgorithm {    protected String routeFile;    private Map<String, List<Integer>> routeNodeMap;    protected static final String DEFAULT_NODE = "DEFAULT_NODE";    protected int keyStartIndex;    protected int keyEndIndex;    protected int valueStartIndex;    protected int valueEndIndex;    public void setKeyStartIndex(int keyStartIndex) {        this.keyStartIndex = keyStartIndex;}    public void setKeyEndIndex(int keyEndIndex) {        this.keyEndIndex = keyEndIndex;}    public void setValueStartIndex(int valueStartIndex) {        this.valueStartIndex = valueStartIndex;}    public void setValueEndIndex(int valueEndIndex) {        this.valueEndIndex = valueEndIndex;}    public void setRouteFile(String routeFile) {        this.routeFile = routeFile;}@Override    public void init() {initialize();}@Override    public Integer calculate(String columnValue) {String key = columnValue.substring(keyStartIndex,keyEndIndex);String value = columnValue.substring(valueStartIndex,valueEndIndex);List<Integer> nodes = routeNodeMap.get(key);        if(nodes == null)nodes = routeNodeMap.get(DEFAULT_NODE);BigInteger bigNum = new BigInteger(""+value.hashCode());        return nodes.get((bigNum.mod(BigInteger.valueOf(nodes.size()))).intValue());}    /*** 读取文件，创建哈希表保存对应关系*/private void initialize() {BufferedReader in = null;        try {            // FileInputStream fin = new FileInputStream(new File(fileMapPath));InputStream fin = this.getClass().getClassLoader().getResourceAsStream(routeFile);            if (fin == null) {                throw new RuntimeException("can't find class resource file "+ routeFile);}            in = new BufferedReader(new InputStreamReader(fin));routeNodeMap = new HashMap<String, List<Integer>>();            for (String line = null; (line = in.readLine()) != null;) {line = line.trim();                if (line.startsWith("#") || line.startsWith("//"))                    continue;                int ind = line.indexOf('=');                if (ind < 0)                    continue;                try {String key = line.substring(0, ind).trim();String value = line.substring(ind+1).trim();String []nodes = value.split(",");List<Integer> values = new ArrayList<Integer>();                    for(int i = 0 ; i< nodes.length ; i++){values.add(Integer.parseInt(nodes[i].trim()));}routeNodeMap.put(key,values);} catch (Exception e) {System.out.println("something wrong in the route hash configuration!");}}} catch (Exception e) {            if (e instanceof RuntimeException) {                throw (RuntimeException) e;} else {                throw new RuntimeException(e);}} finally {            try {                in.close();} catch (Exception e2) {}}}
}

/**
* 实现范围约定的复合规则
*/public class PartitionByScalableRouteHash extends PartitionByRouteHash {    private Map<String,Map<String[],List<Integer>>> routeNodeMap;@Override    public void init() {initialize();}@Override    public Integer calculate(String columnValue) {String key = columnValue.substring(keyStartIndex,keyEndIndex);String value = columnValue.substring(valueStartIndex,valueEndIndex);Map<String[],List<Integer>> scaleMap = routeNodeMap.get(key);        if(scaleMap==null){scaleMap = routeNodeMap.get(this.DEFAULT_NODE);}String []ranges = new String[1];        for(String []range:scaleMap.keySet()){            if(range[0].equals(this.DEFAULT_NODE))                continue;            if(range[0].compareTo(value)<0&&range[1].compareTo(value)>0)ranges = range;}        if(ranges.length==1) {            for(String []range:scaleMap.keySet()){                if(range[0].equals(this.DEFAULT_NODE)){ranges = range;                    break;}}}List<Integer> nodes = scaleMap.get(ranges);BigInteger bigNum = new BigInteger(""+value.hashCode());        return nodes.get((bigNum.mod(BigInteger.valueOf(nodes.size()))).intValue());}    private void initialize(){BufferedReader in = null;        try {            // FileInputStream fin = new FileInputStream(new File(fileMapPath));InputStream fin = this.getClass().getClassLoader().getResourceAsStream(routeFile);            if (fin == null) {                throw new RuntimeException("can't find class resource file "+ routeFile);}            in = new BufferedReader(new InputStreamReader(fin));routeNodeMap = new HashMap<String, Map<String[], List<Integer>>>();            for (String line = null; (line = in.readLine()) != null;) {line = line.trim();                if (line.startsWith("#") || line.startsWith("//"))                    continue;                int lb = line.indexOf('('),rb = line.indexOf(')'),mb = line.indexOf(':');                int ind = line.indexOf('=');                if((lb!=-1&&rb!=-1&&mb!=-1)&&(mb<lb||mb>rb||lb>rb||rb>ind)){                    throw new RuntimeException("Wrong format! Error use of (),:,=!");}                if (ind < 0)                    continue;                try {String key = line.substring(0, lb<0?ind:lb).trim();Map<String[],List<Integer>> scaleMap = routeNodeMap.get(key);                    if(scaleMap == null){scaleMap = new HashMap<String[],List<Integer>>();routeNodeMap.put(key,scaleMap);}String[] valueRange = new String[2];                    if(lb!=-1&&rb!=-1&&mb!=-1) {String minValue = line.substring(lb + 1, mb).trim();String maxValue = line.substring(mb + 1, rb).trim();                        if (minValue.length() != maxValue.length() || minValue.compareTo(maxValue) >= 0) {                            throw new RuntimeException("Wrong value range! ");}valueRange[0] = minValue;valueRange[1] = maxValue;}                    else {valueRange[0] = this.DEFAULT_NODE;}String value = line.substring(ind+1).trim();String []nodes = value.split(",");List<Integer> node = new ArrayList<Integer>();                    for(int i = 0 ; i< nodes.length ; i++){node.add(Integer.parseInt(nodes[i].trim()));}scaleMap.put(valueRange,node);} catch (Exception e) {System.out.println("something wrong in the route hash configuration!");}}} catch (Exception e) {            if (e instanceof RuntimeException) {                throw (RuntimeException) e;} else {                throw new RuntimeException(e);}} finally {            try {                in.close();} catch (Exception e2) {}}}}

之后如果想用这个规则，在rule.xml中添加如下配置即可：

<tableRule name="scalable-route-hash"><rule><columns>order_id</columns><algorithm>scalable-route-hash</algorithm></rule></tableRule><function name="scalable-route-hash" class="org.opencloudb.route.function.PartitionByRouteHash"><property name="routeFile">scalable-route-hash.txt</property><property name="keyStartIndex">0</property><property name="keyEndIndex">5</property><property name="valueStartIndex">5</property><property name="valueEndIndex">11</property></function>

免费体验云安全(易盾)内容安全、验证码等服务

更多网易技术、产品、运营经验分享请点击。

相关文章：
【推荐】 AndroidView的事件分发
【推荐】 Dubbo与HadoopRPC的区别
【推荐】 npm和package.json那些不为常人所知的小秘密