同步图运算框架GraphLite实例之PageRank算法

1.PageRank算法介绍

PageRank，网页排名，又称网页级别、Google左侧排名或佩奇排名，是一种由[1] 根据网页之间相互的超链接计算的技术，而作为网页排名的要素之一，以Google公司创办人拉里·佩奇（Larry Page）之姓来命名。Google用它来体现网页的相关性和重要性，在搜索引擎优化操作中是经常被用来评估网页优化的成效因素之一。Google的创始人拉里·佩奇和谢尔盖·布林于1998年在斯坦福大学发明了这项技术。
PageRank通过网络浩瀚的超链接关系来确定一个页面的等级。Google把从A页面到B页面的链接解释为A页面给B页面投票，Google根据投票来源（甚至来源的来源，即链接到A页面的页面）和投票目标的等级来决定新的等级。简单的说，一个高等级的页面可以使其他低等级页面的等级提升。

2.PageRank算法原理

3.GraphLite图运算系统的PageRank算法实现

/** * @file PageRankVertex.cc * This file implements the PageRank algorithm using graphlite API. */#include <stdio.h>#include <string.h>#include <math.h>#include "GraphLite.h"#define VERTEX_CLASS_NAME(name) PageRankVertex##name#define EPS 1e-6//class PageRankVertexInputFormatter: public InputFormatterclass VERTEX_CLASS_NAME(InputFormatter): public InputFormatter {public:    int64_t getVertexNum() {        unsigned long long n;        sscanf(m_ptotal_vertex_line, "%lld", &n);// read one long long number ,and let n=it        printf("at class PageRankVertexInputFormatter:    m_total_vertex=   %lld \n",n);    m_total_vertex= n;        return m_total_vertex;    }    int64_t getEdgeNum() {        unsigned long long n;        sscanf(m_ptotal_edge_line, "%lld", &n);// read one long long number ,and let n=it        m_total_edge= n;        printf("at class PageRankVertexInputFormatter:   m_total_edge=   %lld \n",n);        return m_total_edge;    }    int getVertexValueSize() {        m_n_value_size = sizeof(double);        return m_n_value_size;    }    int getEdgeValueSize() {        m_e_value_size = sizeof(double);        return m_e_value_size;    }    int getMessageValueSize() {        m_m_value_size = sizeof(double);        return m_m_value_size;    }    void loadGraph() {        unsigned long long last_vertex;        unsigned long long from;        unsigned long long to;        double weight = 0;        double value = 1;//initial PageRank        int outdegree = 0;//outdegree of node        const char *line= getEdgeLine(); // Get edge line, for user. Read from current file offset.                                          // return a string of edge in local subgraph        // Note: modify this if an edge weight is to be read        //       modify the 'weight' variable        sscanf(line, "%lld %lld", &from, &to);//from=source node, to=dest node        addEdge(from, to, &weight);//add one edge form->to weight=0        last_vertex = from;        ++outdegree;        printf("Excute loadGraph()  ,  m_total_edge=  %ld\n",m_total_edge);        for (int64_t i = 1; i < m_total_edge; ++i) {            line= getEdgeLine();// Get edge line, for user. Read from current file offset.                                 // return a string of edge in local subgraph            // Note: modify this if an edge weight is to be read            //       modify the 'weight' variable            sscanf(line, "%lld %lld", &from, &to);            if (last_vertex != from) {                addVertex(last_vertex, &value, outdegree);//addVertex and it's PageRank value,outdegree                last_vertex = from;                outdegree = 1;            } else {                ++outdegree;            }            addEdge(from, to, &weight);        }        addVertex(last_vertex, &value, outdegree);    }};class VERTEX_CLASS_NAME(OutputFormatter): public OutputFormatter {public:    void writeResult() {        int64_t vid;        double value;        char s[1024];        for (ResultIterator r_iter; ! r_iter.done(); r_iter.next() ) {            r_iter.getIdValue(vid, &value);            int n = sprintf(s, "%lld: %f\n", (unsigned long long)vid, value);            writeNextResLine(s, n);        }    }};// An aggregator that records a double value tom compute sum// <double> set the type of m_global and m_local value is doubleclass VERTEX_CLASS_NAME(Aggregator): public Aggregator<double> {public:    void init() {        m_global = 0;  //aggregator global value of AggrValue        m_local = 0;   //aggregator local value of AggrValue    }    void* getGlobal() {        return &m_global;    }    void setGlobal(const void* p) {        m_global = * (double *)p;    }    void* getLocal() {        return &m_local;    }    void merge(const void* p) {        m_global += * (double *)p;         printf("excute merge()  on PageRankAggregator class, m_global= %lf\n",m_global);    }    void accumulate(const void* p) {        m_local += * (double *)p;        printf("excute accumulate()  on PageRankAggregator class, m_local= %lf\n",m_local);    }};class VERTEX_CLASS_NAME(): public Vertex <double, double, double> {public:    void compute(MessageIterator* pmsgs) {        printf("Excute compute(),  MessageIterrator *pmsgs, pmsgs.size=  %d\n ",pmsgs->m_vector_size);        double val;//PageRank value        if (getSuperstep() == 0) {   //Get current superstep number           val= 1.0;  //initial all vertex's PageRank=1  u maybe not initial val there,because we initial val at loadGraph()           printf("getSuperstep()==0     val=%lf\n",getValue());        } else {            if (getSuperstep() >= 2) {                double global_val = * (double *)getAggrGlobal(0);  //Get global value of  aggregator index=0                if (global_val < EPS) {   //judge convergence                        printf("at compute() on PageRankVertex class, global_val==%lf\n",global_val);            voteToHalt(); return;                }            }            double sum = 0;            for ( ; ! pmsgs->done(); pmsgs->next() ) {                sum += pmsgs->getValue();//getValue() on MessageIterator class  return message value.            }            val = 0.15 + 0.85 * sum;            double acc = fabs(getValue() - val);//getValude on Vertex class return vertex value            accumulateAggr(0, &acc);// Accumulate local value of some aggregator. first param is Aggregator index            * mutableValue() = val;        }        //set new PageRank value and then send Message       // * mutableValue() = val;        const int64_t n = getOutEdgeIterator().size();//Get an out-edge iterator.size()        sendMessageToAllNeighbors(val / n);//R_v/L_v   R_v=value  L_v=n    }};class VERTEX_CLASS_NAME(Graph): public Graph {public:    VERTEX_CLASS_NAME(Aggregator)* aggregator;public:    // argv[0]: PageRankVertex.so    // argv[1]: <input path>    // argv[2]: <output path>    void init(int argc, char* argv[]) {        setNumHosts(5);  //machine count=5, one master and 4  workers        setHost(0, "localhost", 1411);        setHost(1, "localhost", 1421);        setHost(2, "localhost", 1431);        setHost(3, "localhost", 1441);        setHost(4, "localhost", 1451);        if (argc < 3) {  //the number of param           printf ("Usage: %s <input path> <output path>\n", argv[0]);           exit(1);        }        m_pin_path = argv[1];//input file path        m_pout_path = argv[2];//output file path        aggregator = new VERTEX_CLASS_NAME(Aggregator)[1];  //define class array  PageRankAggregator[1]        regNumAggr(1);//set  m_aggregator_cnt=param,   aggregator count        regAggr(0, &aggregator[0]);   // m_paggregator[0]= second param ,type:  pointers of AggregatorBase    }    void term() {        delete[] aggregator;    }};/* STOP: do not change the code below. */extern "C" Graph* create_graph() {    Graph* pgraph = new VERTEX_CLASS_NAME(Graph);    pgraph->m_pin_formatter = new VERTEX_CLASS_NAME(InputFormatter);    pgraph->m_pout_formatter = new VERTEX_CLASS_NAME(OutputFormatter);    pgraph->m_pver_base = new VERTEX_CLASS_NAME();    return pgraph;}extern "C" void destroy_graph(Graph* pobject) {    delete ( VERTEX_CLASS_NAME()* )(pobject->m_pver_base);    delete ( VERTEX_CLASS_NAME(OutputFormatter)* )(pobject->m_pout_formatter);    delete ( VERTEX_CLASS_NAME(InputFormatter)* )(pobject->m_pin_formatter);    delete ( VERTEX_CLASS_NAME(Graph)* )pobject;}