Redis 实现“附近的人”功能

/* GEOADD key long lat name [long2 lat2 name2 ... longN latN nameN] */
void geoaddCommand(client *c) {
//参数校验
  /* Check arguments number for sanity. */
  if ((c->argc - 2) % 3 != 0) {
    /* Need an odd number of arguments if we got this far... */
    addReplyError(c, "syntax error. Try GEOADD key [x1] [y1] [name1] "
             "[x2] [y2] [name2] ... ");
    return;
  }
//参数提取Redis
  int elements = (c->argc - 2) / 3;
  int argc = 2+elements*2; /* ZADD key score ele ... */
  robj **argv = zcalloc(argc*sizeof(robj*));
  argv[0] = createRawStringObject("zadd",4);
  argv[1] = c->argv[1]; /* key */
  incrRefCount(argv[1]);
//参数遍历+转换
  /* Create the argument vector to call ZADD in order to add all
   * the score,value pairs to the requested zset, where score is actually
   * an encoded version of lat,long. */
  int i;
  for (i = 0; i < elements; i++) {
    double xy[2];
  //提取经纬度
    if (extractLongLatOrReply(c, (c->argv+2)+(i*3),xy) == C_ERR) {
      for (i = 0; i < argc; i++)
        if (argv[i]) decrRefCount(argv[i]);
      zfree(argv);
      return;
    }
  //将经纬度转换为52位的geohash作为分值 & 提取对象名称
    /* Turn the coordinates into the score of the element. */
    GeoHashBits hash;
    geohashEncodeWGS84(xy[0], xy[1], GEO_STEP_MAX, &hash);
    GeoHashFix52Bits bits = geohashAlign52Bits(hash);
    robj *score = createObject(OBJ_STRING, sdsfromlonglong(bits));
    robj *val = c->argv[2 + i * 3 + 2];
  //设置有序集合的对象元素名称和分值
    argv[2+i*2] = score;
    argv[3+i*2] = val;
    incrRefCount(val);
  }
//调用zadd命令，存储转化好的对象
  /* Finally call ZADD that will do the work for us. */
  replaceClientCommandVector(c,argc,argv);
  zaddCommand(c);
}

GEORADIUS key longitude latitude radius m|km|ft|mi [WITHCOORD] [WITHDIST] [WITHHASH] [ASC|DESC] [COUNT count] [STORE key] [STORedisT key]

["member1","member2","member3"]

[
["member1", distance1, [longitude1, latitude1]]
["member2", distance2, [longitude2, latitude2]]
]

/* GEORADIUS key x y radius unit [WITHDIST] [WITHHASH] [WITHCOORD] [ASC|DESC]
 *                [COUNT count] [STORE key] [STORedisT key]
 * GEORADIUSBYMEMBER key member radius unit ... options ... */
void georadiusGeneric(client *c, int flags) {
  robj *key = c->argv[1];
  robj *storekey = NULL;
  int stoRedist = 0; /* 0 for STORE, 1 for STORedisT. */
//根据key获取有序集合
  robj *zobj = NULL;
  if ((zobj = lookupKeyReadOrReply(c, key, shared.null[c->resp])) == NULL ||
    checkType(c, zobj, OBJ_ZSET)) {
    return;
  }
//根据用户输入（经纬度/member）确认中心点经纬度
  int base_args;
  double xy[2] = { 0 };
  if (flags & RADIUS_COORDS) {
……
  }
//获取查询范围距离
  double radius_meters = 0, conversion = 1;
  if ((radius_meters = extractDistanceOrReply(c, c->argv + base_args - 2,
                        &conversion)) < 0) {
    return;
  }
//获取可选参数 （withdist、withhash、withcoords、sort、count）
  int withdist = 0, withhash = 0, withcoords = 0;
  int sort = SORT_NONE;
  long long count = 0;
  if (c->argc > base_args) {
    ... ...
  }
//获取 STORE 和 STORedisT 参数
  if (storekey && (withdist || withhash || withcoords)) {
    addReplyError(c,
      "STORE option in GEORADIUS is not compatible with "
      "WITHDIST, WITHHASH and WITHCOORDS options");
    return;
  }
//设定排序
  if (count != 0 && sort == SORT_NONE) sort = SORT_ASC;
//利用中心点和半径计算目标区域范围
  GeoHashRadius georadius =
    geohashGetAreasByRadiusWGS84(xy[0], xy[1], radius_meters);
//对中心点及其周围8个geohash网格区域进行查找，找出范围内元素对象
  geoArray *ga = geoArrayCreate();
  membersOfAllNeighbors(zobj, georadius, xy[0], xy[1], radius_meters, ga);
//未匹配返空
  /* If no matching results, the user gets an empty reply. */
  if (ga->used == 0 && storekey == NULL) {
    addReplyNull(c);
    geoArrayFree(ga);
    return;
  }
//一些返回值的设定和返回
  ……
  geoArrayFree(ga);
}

// geohash_helper.c
GeoHashRadius geohashGetAreasByRadiusWGS84(double longitude, double latitude,
                      double radius_meters) {
  return geohashGetAreasByRadius(longitude, latitude, radius_meters);
}
//返回能够覆盖目标区域范围的9个geohashBox
GeoHashRadius geohashGetAreasByRadius(double longitude, double latitude, double radius_meters) {
//一些参数设置
  GeoHashRange long_range, lat_range;
  GeoHashRadius radius;
  GeoHashBits hash;
  GeoHashNeighbors neighbors;
  GeoHashArea area;
  double min_lon, max_lon, min_lat, max_lat;
  double bounds[4];
  int steps;
//计算目标区域外接矩形的经纬度范围（目标区域为：以目标经纬度为中心，半径为指定距离的圆）
  geohashBoundingBox(longitude, latitude, radius_meters, bounds);
  min_lon = bounds[0];
  min_lat = bounds[1];
  max_lon = bounds[2];
  max_lat = bounds[3];
//根据目标区域中心点纬度和半径，计算带查询的9个搜索框的geohash精度（位）
//这里用到latitude主要是针对极地的情况对精度进行了一些调整（纬度越高，位数越小）
  steps = geohashEstimateStepsByRadius(radius_meters,latitude);
//设置经纬度最大最小值：-180<=longitude<=180, -85<=latitude<=85
  geohashGetCoordRange(&long_range,&lat_range);
//将待查经纬度按指定精度（steps）编码成geohash值
  geohashEncode(&long_range,&lat_range,longitude,latitude,steps,&hash);
//将geohash值在8个方向上进行扩充，确定周围8个Box（neighbors）
  geohashNeighbors(&hash,&neighbors);
//根据hash值确定area经纬度范围
  geohashDecode(long_range,lat_range,hash,&area);
//一些特殊情况处理
  ……
//构建并返回结果  
  radius.hash = hash;
  radius.neighbors = neighbors;
  radius.area = area;
  return radius;
}

// geo.c
//在9个hashBox中获取想要的元素
int membersOfAllNeighbors(robj *zobj, GeoHashRadius n, double lon, double lat, double radius, geoArray *ga) {
  GeoHashBits neighbors[9];
  unsigned int i, count = 0, last_processed = 0;
  int debugmsg = 0;
//获取9个搜索hashBox
  neighbors[0] = n.hash;
  neighbors[8] = n.neighbors.south_west;
//在每个hashBox中搜索目标点
  for (i = 0; i < sizeof(neighbors) / sizeof(*neighbors); i++) {
    if (HASHISZERO(neighbors[i])) {
      if (debugmsg) D("neighbors[%d] is zero",i);
      continue;
    }
//剔除可能的重复hashBox (搜索半径>5000KM时可能出现)
    if (last_processed &&
      neighbors[i].bits == neighbors[last_processed].bits &&
      neighbors[i].step == neighbors[last_processed].step)
    {
      continue;
    }
//搜索hashBox中满足条件的对象  
    count += membersOfGeoHashBox(zobj, neighbors[i], ga, lon, lat, radius);
    last_processed = i;
  }
  return count;
}
int membersOfGeoHashBox(robj *zobj, GeoHashBits hash, geoArray *ga, double lon, double lat, double radius) {
//获取hashBox内的最大、最小geohash值（52位）
  GeoHashFix52Bits min, max;
  scoresOfGeoHashBox(hash,&min,&max);
//根据最大、最小geohash值筛选zobj集合中满足条件的点
  return geoGetPointsInRange(zobj, min, max, lon, lat, radius, ga);
}
int geoGetPointsInRange(robj *zobj, double min, double max, double lon, double lat, double radius, geoArray *ga) {
//搜索Range的参数边界设置（即9个hashBox其中一个的边界范围）
  zrangespec range = { .min = min, .max = max, .minex = 0, .maxex = 1 };
  size_t origincount = ga->used;
  sds member;
//搜索集合zobj可能有ZIPLIST和SKIPLIST两种编码方式，这里以SKIPLIST为例，逻辑是一样的
  if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
    ……
  } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
    zset *zs = zobj->ptr;
    zskiplist *zsl = zs->zsl;
    zskiplistNode *ln;
//获取在hashBox范围内的首个元素（跳表数据结构，效率可比拟于二叉查找树），没有则返0
    if ((ln = zslFirstInRange(zsl, &range)) == NULL) {
      /* Nothing exists starting at our min. No results. */
      return 0;
    }
//从首个元素开始遍历集合
    while (ln) {
      sds ele = ln->ele;
//遍历元素超出range范围则break
      /* Abort when the node is no longer in range. */
      if (!zslValueLteMax(ln->score, &range))
        break;
//元素校验（计算元素与中心点的距离）
      ele = sdsdup(ele);
      if (geoAppendIfWithinRadius(ga,lon,lat,radius,ln->score,ele)
        == C_ERR) sdsfree(ele);
      ln = ln->level[0].forward;
    }
  }
  return ga->used - origincount;
}
int geoAppendIfWithinRadius(geoArray *ga, double lon, double lat, double radius, double score, sds member) {
  double distance, xy[2];
//解码错误, 返回error
  if (!decodeGeohash(score,xy)) return C_ERR; /* Can't decode. */
//最终距离校验(计算球面距离distance看是否小于radius)
  if (!geohashGetDistanceIfInRadiusWGS84(lon,lat, xy[0], xy[1],
                      radius, &distance))
  {
    return C_ERR;
  }
//构建并返回满足条件的元素
  geoPoint *gp = geoArrayAppend(ga);
  gp->longitude = xy[0];
  gp->latitude = xy[1];
  gp->dist = distance;
  gp->member = member;
  gp->score = score;
  return C_OK;
}