Redis高效检索地理位置的原理解析

static void geohash_move_x(GeoHashBits *hash, int8_t d) {
if (d == 0)
return;

uint64_t x = hash->bits & 0xaaaaaaaaaaaaaaaaULL;
uint64_t y = hash->bits & 0x5555555555555555ULL;

uint64_t zz = 0x5555555555555555ULL >> (64 – hash->step * 2);

if (d > 0) {
x = x + (zz + 1);
} else {
x = x | zz;
x = x – (zz + 1);
}

x &= (0xaaaaaaaaaaaaaaaaULL >> (64 – hash->step * 2));
hash->bits = (x | y);
}

static void geohash_move_y(GeoHashBits *hash, int8_t d) {
if (d == 0)
return;

uint64_t x = hash->bits & 0xaaaaaaaaaaaaaaaaULL;
uint64_t y = hash->bits & 0x5555555555555555ULL;

uint64_t zz = 0xaaaaaaaaaaaaaaaaULL >> (64 – hash->step * 2);
if (d > 0) {
y = y + (zz + 1);
} else {
y = y | zz;
y = y – (zz + 1);
}
y &= (0x5555555555555555ULL >> (64 – hash->step * 2));
hash->bits = (x | y);
}

/* GEOADD key [CH] [NX|XX] long lat name [long2 lat2 name2 … longN latN nameN] */
void geoaddCommand(client *c) {
int xx = 0, nx = 0, longidx = 2;
int i;

/* 解析可选参数 */
while (longidx < c->argc) {
char *opt = c->argv[longidx]->ptr;
if (!strcasecmp(opt,”nx”)) nx = 1;
else if (!strcasecmp(opt,”xx”)) xx = 1;
else if (!strcasecmp(opt,”ch”)) {}
else break;
longidx++;
}

if ((c->argc – longidx) % 3 || (xx && nx)) {
/* 解析所有的经纬度值和member，并对其个数做校验 */
addReplyErrorObject(c,shared.syntaxerr);
return;
}

/* 构建zadd的参数数组 */
int elements = (c->argc – longidx) / 3;
int argc = longidx+elements*2; /* ZADD key [CH] [NX|XX] score ele … */
robj **argv = zcalloc(argc*sizeof(robj*));
argv[0] = createRawStringObject(“zadd”,4);
for (i = 1; i < longidx; i++) {
argv[i] = c->argv[i];
incrRefCount(argv[i]);
}

/* 以3个参数为一组，将所有的经纬度和member信息从参数列表里解析出来，并放到zadd的参数数组中 */
for (i = 0; i < elements; i++) {
double xy[2];

if (extractLongLatOrReply(c, (c->argv+longidx)+(i*3),xy) == C_ERR) {
for (i = 0; i < argc; i++)
if (argv[i]) decrRefCount(argv[i]);
zfree(argv);
return;
}

/* 将经纬度坐标转化成score信息 */
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[longidx + i * 3 + 2];
argv[longidx+i*2] = score;
argv[longidx+1+i*2] = val;
incrRefCount(val);
}

/* 转化成zadd命令所需要的参数格式*/
replaceClientCommandVector(c,argc,argv);
zaddCommand(c);
}

void georadiusGeneric(client *c, int srcKeyIndex, int flags) {
robj *storekey = NULL;
int storedist = 0; /* 0 for STORE, 1 for STOREDIST. */

/* 根据key找找到对应的zojb */
robj *zobj = NULL;
if ((zobj = lookupKeyReadOrReply(c, c->argv[srcKeyIndex], shared.emptyarray)) == NULL ||
checkType(c, zobj, OBJ_ZSET)) {
return;
}

/* 解析请求中的经纬度值 */
int base_args;
GeoShape shape = {0};
if (flags & RADIUS_COORDS) {
/*
* 各种必选参数的解析，省略细节代码，主要是解析坐标点信息和半径
*/
}

/* 解析所有的可选参数. */
int withdist = 0, withhash = 0, withcoords = 0;
int frommember = 0, fromloc = 0, byradius = 0, bybox = 0;
int sort = SORT_NONE;
int any = 0; /* any=1 means a limited search, stop as soon as enough results were found. */
long long count = 0; /* Max number of results to return. 0 means unlimited. */
if (c->argc > base_args) {
/*
* 各种可选参数的解析，省略细节代码
*/
}

/* Get all neighbor geohash boxes for our radius search
* 获取到要查找范围内所有的9个geo邻域 */
GeoHashRadius georadius = geohashCalculateAreasByShapeWGS84(&shape);

/* 创建geoArray存储结果列表 */
geoArray *ga = geoArrayCreate();
/* 扫描9个区域中是否有满足条的点，有就放到geoArray中 */
membersOfAllNeighbors(zobj, georadius, &shape, ga, any ? count : 0);

/* 如果没有匹配结果，返回空对象 */
if (ga->used == 0 && storekey == NULL) {
addReply(c,shared.emptyarray);
geoArrayFree(ga);
return;
}

long result_length = ga->used;
long returned_items = (count == 0 || result_length < count) ?
result_length : count;
long option_length = 0;

/*
* 后续一些参数逻辑，比如处理排序，存储……
*/
// 释放geoArray占用的空间
geoArrayFree(ga);
}