菜鸟末端轨迹(解密支撑每天251亿个包裹的数据库) - 阿里云RDS PostgreSQL最佳实践

背景

菜鸟末端轨迹项目中涉及的一个关键需求，面面判断。

在数据库中存储了一些多边形记录，约几百万到千万条记录，例如一个小区，在地图上是一个多边形。

不同的快递公司，会有各自不同的多边形划分方法（每个网点负责的片区(多边形)，每个快递员负责的片区(多边形)）。

用户在寄件时，根据用户的位置，查找对应快递公司负责这个片区的网点、或者负责该片区的快递员。

一、需求

1、在数据库中存储了一些静态的面信息，代表小区、园区、写字楼等等。所有的面不相交。

2、为了支持不同的业务类型，对一个地图，可能划分为不同的多边形组成。

例如不同的快递公司，会有各自不同的多边形划分方法（网点负责的片区(多边形)，某个快递员负责的片区(多边形)）。

因此在一张地图上，有多个图层，每个图层的多边形划分方法可能不一样。

3、快速的根据快递公司、客户的位置，求包含这个点的多边形（即得到对应快递公司负责这个片区的网点、或者负责该片区的快递员）。

二、架构设计

用到阿里云的RDS PostgreSQL，以及PG提供的PostGIS插件。

我们需要用到PostGIS的函数有两个

http://postgis.net/docs/manual-2.3/ST_Within.html

1、ST_within

ST_Within — Returns true if the geometry A is completely inside geometry B

boolean ST_Within(geometry A, geometry B);

Returns TRUE if geometry A is completely inside geometry B. For this function to make sense, the source geometries must both be of the same coordinate projection, having the same SRID. It is a given that if ST_Within(A,B) is true and ST_Within(B,A) is true, then the two geometries are considered spatially equal.

This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries. To avoid index use, use the function _ST_Within.

-- a circle within a circle
SELECT ST_Within(smallc,smallc) As smallinsmall,
        ST_Within(smallc, bigc) As smallinbig,
        ST_Within(bigc,smallc) As biginsmall,
        ST_Within(ST_Union(smallc, bigc), bigc) as unioninbig,
        ST_Within(bigc, ST_Union(smallc, bigc)) as biginunion,
        ST_Equals(bigc, ST_Union(smallc, bigc)) as bigisunion
FROM
(
SELECT ST_Buffer(ST_GeomFromText('POINT(50 50)'), 20) As smallc,
        ST_Buffer(ST_GeomFromText('POINT(50 50)'), 40) As bigc) As foo;
-- Result
 smallinsmall | smallinbig | biginsmall | unioninbig | biginunion | bigisunion
--------------+------------+------------+------------+------------+------------
 t            | t          | f          | t          | t          | t
(1 row)

2、ST_Contains

ST_Contains — Returns true if and only if no points of B lie in the exterior of A, and at least one point of the interior of B lies in the interior of A.

boolean ST_Contains(geometry geomA, geometry geomB);

Returns TRUE if geometry B is completely inside geometry A. For this function to make sense, the source geometries must both be of the same coordinate projection, having the same SRID. ST_Contains is the inverse of ST_Within. So ST_Contains(A,B) implies ST_Within(B,A) except in the case of invalid geometries where the result is always false regardless or not defined.

This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries. To avoid index use, use the function _ST_Contains.

-- A circle within a circle
SELECT ST_Contains(smallc, bigc) As smallcontainsbig,
           ST_Contains(bigc,smallc) As bigcontainssmall,
           ST_Contains(bigc, ST_Union(smallc, bigc)) as bigcontainsunion,
           ST_Equals(bigc, ST_Union(smallc, bigc)) as bigisunion,
           ST_Covers(bigc, ST_ExteriorRing(bigc)) As bigcoversexterior,
           ST_Contains(bigc, ST_ExteriorRing(bigc)) As bigcontainsexterior
FROM (SELECT ST_Buffer(ST_GeomFromText('POINT(1 2)'), 10) As smallc,
                         ST_Buffer(ST_GeomFromText('POINT(1 2)'), 20) As bigc) As foo;      

-- Result
  smallcontainsbig | bigcontainssmall | bigcontainsunion | bigisunion | bigcoversexterior | bigcontainsexterior
------------------+------------------+------------------+------------+-------------------+---------------------
 f                | t                | t                | t          | t        | f      

-- Example demonstrating difference between contains and contains properly
SELECT ST_GeometryType(geomA) As geomtype, ST_Contains(geomA,geomA) AS acontainsa, ST_ContainsProperly(geomA, geomA) AS acontainspropa,
   ST_Contains(geomA, ST_Boundary(geomA)) As acontainsba, ST_ContainsProperly(geomA, ST_Boundary(geomA)) As acontainspropba
FROM (VALUES ( ST_Buffer(ST_Point(1,1), 5,1) ),
                         ( ST_MakeLine(ST_Point(1,1), ST_Point(-1,-1) ) ),
                         ( ST_Point(1,1) )
          ) As foo(geomA);      

  geomtype    | acontainsa | acontainspropa | acontainsba | acontainspropba
--------------+------------+----------------+-------------+-----------------
ST_Polygon    | t          | f              | f           | f
ST_LineString | t          | f              | f           | f
ST_Point      | t          | t              | f           | f

三、DEMO与性能

1 PG内置几何类型面点搜索压测

为了简化测试，采样PG内置的几何类型进行测试，用法与PostGIS是类似的。

1、创建测试表

postgres=# create table po(id int, typid int, po polygon);
CREATE TABLE

2、创建分区表或分区索引

create extension btree_gist;
create index idx_po_1 on po using gist(typid, po);

3、创建空间排他约束，可选

如果要求单个typid内的po不重叠，可以创建空间排他约束

create table tbl_po(id int, typid int, po polygon)
PARTITION BY LIST (typid);    

CREATE TABLE tbl_po_1
    PARTITION OF tbl_po (
    EXCLUDE USING gist (po WITH &&)
) FOR VALUES IN (1);    

...    

CREATE TABLE tbl_po_20
    PARTITION OF tbl_po (
    EXCLUDE USING gist (po WITH &&)
) FOR VALUES IN (20);    

查看某分区表的空间排他约束如下    

postgres=# \d tbl_po_1
             Table "postgres.tbl_po_1"
 Column |  Type   | Collation | Nullable | Default
--------+---------+-----------+----------+---------
 id     | integer |           |          |
 typid  | integer |           |          |
 po     | polygon |           |          |
Partition of: tbl_po FOR VALUES IN (1)
Indexes:
    "tbl_po_1_po_excl" EXCLUDE USING gist (po WITH &&)

4、写入1000万多边形测试数据

insert into po select id, random()*20, polygon('(('||x1||','||y1||'),('||x2||','||y2||'),('||x3||','||y3||'))') from (select id, 180-random()*180 x1, 180-random()*180 x2, 180-random()*180 x3, 90-random()*90 y1, 90-random()*90 y2, 90-random()*90 y3 from generate_series(1,10000000) t(id)) t;

5、测试面点判断性能

查询包含point(1,1)的多边形，响应时间0.57毫秒。

postgres=# explain (analyze,verbose,timing,costs,buffers) select * from po where typid=1 and po @> polygon('((1,1),(1,1),(1,1))') limit 1;
                                                           QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=0.42..1.76 rows=1 width=93) (actual time=0.551..0.551 rows=1 loops=1)
   Output: id, typid, po
   Buffers: shared hit=74
   ->  Index Scan using idx_po_1 on postgres.po  (cost=0.42..673.48 rows=503 width=93) (actual time=0.550..0.550 rows=1 loops=1)
         Output: id, typid, po
         Index Cond: ((po.typid = 1) AND (po.po @> '((1,1),(1,1),(1,1))'::polygon))
         Rows Removed by Index Recheck: 17
         Buffers: shared hit=74
 Planning time: 0.090 ms
 Execution time: 0.572 ms
(10 rows)

6、压测

vi test.sql
\set x random(-180,180)
\set y random(-90,90)
\set typid random(1,20)
select * from po where typid=:typid and po @> polygon('((:x,:y),(:x,:y),(:x,:y))') limit 1;   

pgbench -M simple -n -r -P 1 -f ./test.sql -c 64 -j 64 -T 100
transaction type: ./test.sql
scaling factor: 1
query mode: simple
number of clients: 64
number of threads: 64
duration: 100 s
number of transactions actually processed: 29150531
latency average = 0.220 ms
latency stddev = 0.140 ms
tps = 291487.813205 (including connections establishing)
tps = 291528.228634 (excluding connections establishing)
script statistics:
 - statement latencies in milliseconds:
         0.002  \set x random(-180,180)
         0.001  \set y random(-90,90)
         0.000  \set typid random(1,20)
         0.223  select * from po where typid=:typid and po @> polygon('((:x,:y),(:x,:y),(:x,:y))') limit 1;

惊不惊喜、意不意外

TPS：29万，平均响应时间：0.2毫秒

2 PostGIS空间数据库面点搜索压测

阿里云 RDS PostgreSQL，HybridDB for PostgreSQL 已经内置了PostGIS空间数据库插件，使用前创建插件即可。

create extension postgis;

1、建表

postgres=# create table po(id int, typid int, po geometry);
CREATE TABLE

2、创建空间索引

postgres=# create extension btree_gist;
postgres=# create index idx_po_1 on po using gist(typid, po);

3、写入1000万多边形测试数据

postgres=# insert into po
select
  id, random()*20,
  ST_PolygonFromText('POLYGON(('||x1||' '||y1||','||x2||' '||y2||','||x3||' '||y3||','||x1||' '||y1||'))')
from
(
  select id, 180-random()*180 x1, 180-random()*180 x2, 180-random()*180 x3, 90-random()*90 y1, 90-random()*90 y2, 90-random()*90 y3 from generate_series(1,10000000) t(id)
) t;

4、测试面点判断性能

postgres=# explain (analyze,verbose,timing,costs,buffers) select * from po where typid=1 and st_within(ST_PointFromText('POINT(1 1)'), po) limit 1;
                                                         QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=0.42..4.21 rows=1 width=40) (actual time=0.365..0.366 rows=1 loops=1)
   Output: id, typid, po
   Buffers: shared hit=14
   ->  Index Scan using idx_po_1 on public.po  (cost=0.42..64.92 rows=17 width=40) (actual time=0.364..0.364 rows=1 loops=1)
         Output: id, typid, po
         Index Cond: ((po.typid = 1) AND (po.po ~ '0101000000000000000000F03F000000000000F03F'::geometry))
         Filter: _st_contains(po.po, '0101000000000000000000F03F000000000000F03F'::geometry)
         Rows Removed by Filter: 1
         Buffers: shared hit=14
 Planning time: 0.201 ms
 Execution time: 0.389 ms
(11 rows)  

postgres=# select id,typid,st_astext(po) from po where typid=1 and st_within(ST_PointFromText('POINT(1 1)'), po) limit 5;
   id    | typid |                                                                       st_astext
---------+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------
 9781228 |     1 | POLYGON((0.295946141704917 0.155529817566276,16.4715472329408 56.1022255802527,172.374844718724 15.4784881789237,0.295946141704917 0.155529817566276))
  704428 |     1 | POLYGON((173.849076312035 77.8871315997094,167.085936572403 23.9897218951955,0.514283403754234 0.844541620463133,173.849076312035 77.8871315997094))
 5881120 |     1 | POLYGON((104.326644698158 44.4173073163256,3.76680867746472 76.8664212757722,0.798425730317831 0.138536808080971,104.326644698158 44.4173073163256))
 1940693 |     1 | POLYGON((0.774057107046247 0.253543308936059,126.49553722702 22.7823389600962,8.62134614959359 56.176855028607,0.774057107046247 0.253543308936059))
 3026739 |     1 | POLYGON((0.266327261924744 0.406031627207994,101.713274326175 38.6256391229108,2.88589236326516 15.3229149011895,0.266327261924744 0.406031627207994))
(5 rows)

5、压测

vi test.sql
\setrandom x -180 180
\setrandom y -90 90
\setrandom typid 1 20
select * from po where typid=:typid and st_within(ST_PointFromText('POINT(:x :y)'), po) limit 1;    

pgbench -M simple -n -r -P 1 -f ./test.sql -c 64 -j 64 -T 120
transaction type: Custom query
scaling factor: 1
query mode: simple
number of clients: 64
number of threads: 64
duration: 120 s
number of transactions actually processed: 23779817
latency average: 0.321 ms
latency stddev: 0.255 ms
tps = 198145.452614 (including connections establishing)
tps = 198160.891580 (excluding connections establishing)
statement latencies in milliseconds:
        0.002615        \setrandom x -180 180
        0.000802        \setrandom y -90 90
        0.000649        \setrandom typid 1 20
        0.316816        select * from po where typid=:typid and st_within(ST_PointFromText('POINT(:x :y)'), po) limit 1;

惊不惊喜、意不意外

TPS：19.8万，平均响应时间：0.32毫秒

四、技术点

1、空间排他约束

这个约束可以用于强制记录中的多边形不相交。例如地图这类严谨数据，绝对不可能出现两个多边形相交的，否则就有领土纷争了。

PostgreSQL就是这么严谨，意不意外。

2、分区表

本例中不同的快递公司，对应不同的图层，每个快递公司根据网点、快递员负责的片区(多边形)划分为多个多边形。

使用LIST分区，每个分区对应一家快递公司。

3、空间索引

GiST空间索引，支持KNN、包含、相交、上下左右等空间搜索。

效率极高。

4、空间分区索引

《分区索引的应用和实践 - 阿里云RDS PostgreSQL最佳实践》

5、面面、点判断

面面判断或面点判断是本例的主要需求，用户在寄包裹时，根据用户位置在数据库的一千万多边形中找出覆盖这个点的多边形。

五、云端产品

阿里云 RDS PostgreSQL

六、类似场景、案例

《PostgreSQL 物流轨迹系统数据库需求分析与设计 - 包裹侠实时跟踪与召回》

七、小结