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

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

作者

digoal

日期

2017-08-03

标签

PostgreSQL , PostGIS , 多边形 , 面 , 点 , 面点判断 , 菜鸟

---

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

注意&&是指多边形的bound box相交时返回TRUE，所以可能导致实际不相交但是bound box相交的两个对象不能同时入口。

为了解决这个问题，可以使用本文末尾用到的函数写入方法，不要直接INSERT，也不要使用exclude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bound box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。

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

注意&&是指多边形的bound box相交时返回TRUE，所以可能导致实际不相交但是bound box相交的两个对象不能同时入口。

解决这个问题的方法，使用函数写入，在函数中使用pg_try_advisory_xact_lock和ST_Intersects保证约束的一致性，不用担心并发写导致约束不可靠的问题。

postgres=# select ST_Intersects(st_makepolygon(ST_LineFromText('LINESTRING(1 1,2 1,1.5 2,1 1)') ), st_makepolygon(ST_LineFromText('LINESTRING(1.9 1.9,3 1.9,2.5 3,1.9 1.9)') ));st_intersects 
---------------f
(1 row)postgres=# select st_makepolygon(ST_LineFromText('LINESTRING(1 1,2 1,1.5 2,1 1)') ) && st_makepolygon(ST_LineFromText('LINESTRING(1.9 1.9,3 1.9,2.5 3,1.9 1.9)') );?column? 
----------t
(1 row)create table tbl(id int, geo geometry);
create index idx_tbl_1 on tbl using gist (geo);create or replace function insert_tbl (int, geometry) returns void as $$
declarevid int;var geometry;
beginloopif pg_try_advisory_xact_lock(1) then -- 串行写select geo into var from tbl where ST_Intersects(geo, $2) limit 1;if not found theninsert into tbl (id, geo) values ($1, $2);return;elseraise notice '% intersect with %,%, this row not inserted.', $2, vid,var;return;end if;end if;end loop;
end;
$$ language plpgsql strict;postgres=# select insert_tbl(1,st_makepolygon(ST_LineFromText('LINESTRING(1 1,2 1,1.5 2,1 1)') ));insert_tbl 
------------(1 row)postgres=# select insert_tbl(1,st_makepolygon(ST_LineFromText('LINESTRING(1 1,2 1,1.5 2,1 1)') ));
NOTICE:  01030000000100000004000000000000000000F03F000000000000F03F0000000000000040000000000000F03F000000000000F83F0000000000000040000000000000F03F000000000000F03F intersect with <NULL>,01030000000100000004000000000000000000F03F000000000000F03F0000000000000040000000000000F03F000000000000F83F0000000000000040000000000000F03F000000000000F03F, this row not inserted.insert_tbl 
------------(1 row)postgres=# select insert_tbl(1,st_makepolygon(ST_LineFromText('LINESTRING(1.9 1.9,3 1.9,2.5 3,1.9 1.9)') ));insert_tbl 
------------(1 row)

http://postgis.net/docs/manual-2.5/ST_Intersects.html

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

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（网点负责的片区(多边形)，某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。

使用阿里云RDS PostgreSQL，用户存放约1千万的多边形数据，单库实现了每秒29万的处理请求，单次请求平均响应时间约0.2毫秒。

惊不惊喜、意不意外。

八、参考

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

a

以上内容
来源 https://github.com/digoal/blog/blob/master/201708/20170803_01.md