如何加快对地理位置过程的查询

Question

我有一个包含 10,301,390 个 GPS 记录、城市、国家和 IP 地址块的表。我有用户当前的经纬度位置。我创建了这个查询：

SELECT
  *, point(45.1013021, 46.3021011) <@> point(latitude, longitude) :: point AS distance
FROM
  locs
WHERE
  (
    point(45.1013021, 46.3021011) <@> point(latitude, longitude)
  ) < 10 -- radius
ORDER BY
  distance LIMIT 1;

这个查询成功地给了我我想要的东西，但它很慢。根据给定的纬度和经度，获得一条记录需要 2 到 3 秒。

我在latitude和longitude列上尝试了 B 树索引，也尝试过，GIST( point(latitude, longitude));但查询仍然很慢。

我怎样才能加快这个查询？

更新：

似乎缓慢是由 引起的，ORDER BY但我想获得最短距离，所以问题仍然存在。

Answer 1

您可以考虑使用基于使用函数的 GIST 索引ll_to_earth。该索引将允许快速“附近”搜索。

CREATE INDEX 
   ON locs USING gist (ll_to_earth(lat, lng));

一旦你有了这个索引，你的查询应该以不同的方式完成。

您的 (lat, lng) 对需要转换为earth类型，并与索引值（相同类型）进行比较。您的查询需要有两个条件，一个是“近似”结果，一个是“精确”结果。第一个将能够使用以前的索引：

SELECT
    *
FROM
    locs
WHERE
    /* First condition allows to search for points at an approximate distance:
       a distance computed using a 'box', instead of a 'circumference'.
       This first condition will use the index.
       (45.1013021, 46.3021011) = (lat, lng) of search center. 
       25000 = search radius (in m)
    */
    earth_box(ll_to_earth(45.1013021, 46.3021011), 25000) @> ll_to_earth(lat, lng) 

    /* This second condition (which is slower) will "refine" 
       the previous search, to include only the points within the
       circumference.
    */
    AND earth_distance(ll_to_earth(45.1013021, 46.3021011), 
             ll_to_earth(lat, lng)) < 25000 ;

要使用此代码，您需要两个扩展（包含在大多数 PostgreSQL 发行版中）：

CREATE EXTENSION IF NOT EXISTS cube ;
CREATE EXTENSION IF NOT EXISTS earthdistance;

这是他们的文档：

• 立方体。您应该查看@> 运算符的说明。下一个需要这个模块。
• 地球距离。您将在此处找到有关earth_box和 的信息earth_distance。该模块假设地球是球形的，这对于大多数应用程序来说是一个足够好的近似值。

一个由来自自由世界城市数据库的 220 万行组成的表的测试为我提供了对上一个查询的以下答案（与您的不完全相同）：

"ru","andra-ata","Andra-Ata","24",,44.9509,46.3327
"ru","andratinskiy","Andratinskiy","24",,44.9509,46.3327
"ru","chernozemelskaya","Chernozemelskaya","24",,44.9821,46.0622
"ru","gayduk","Gayduk","24",,44.9578,46.5244
"ru","imeni beriya","Imeni Beriya","24",,45.0208,46.3906
"ru","imeni kirova","Imeni Kirova","24",,45.2836,46.4847
"ru","kumskiy","Kumskiy","24",,44.9821,46.0622
"ru","kumskoy","Kumskoy","24",,44.9821,46.0622
"ru","lopas","Lopas","17",,44.937,46.1833
"ru","pyatogo dekabrya","Pyatogo Dekabrya","24",,45.1858,46.1656
"ru","svetlyy erek","Svetlyy Erek","24",,45.0079,46.4408
"ru","ulan tuk","Ulan Tuk","24",,45.1542,46.1097

对时间有一个“数量级”的想法：pgAdmin III 告诉我获得这个答案的时间是 22 毫秒。（带有“开箱即用”参数的 PostgreSQL 9.6.1，在装有 Mac OS 10.12、Core i7、SSD 的 Mac 上）