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Using UDFs for Geo-Distance Search in MySQL_MySQL

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Originally written by Alexander Rubin

In my previous post about geo-spatial search in MySQL I described (along with other things) how to use geo-distance functions. In this post I will describe the geo-spatial distance functions in more details.

If you need to calculate an exact distance between 2 points on Earth in MySQL (very common for geo-enabled applications) you have at least 3 choices.

  • Use stored function and implement  haversine  formula
  • Use UDF (user defined function) for haversine (see below)
  • In MySQL 5.6 you can use st_distance function (newly documented), however, you will get the distance on plane and not on earth; the value returned will be good for sorting by distance but will not represent actual miles or kilometers.

MySQL stored function for calculating distance on Earth

I previously gave an example for a MySQL-stored function which implements the haversine formula. However, the approach I used was not very precise: it was optimized for speed. If you need a more precise haversine formula implementation you can use this function (result will be in miles):

delimiter //create DEFINER = CURRENT_USER function haversine_distance_sp (lat1 double, lon1 double, lat2 double, lon2 double) returns double begin declare R int DEFAULT 3958.76; declare phi1 double; declare phi2 double; declare d_phi double; declare d_lambda double; declare a double; declare c double; declare d double; set phi1 = radians(lat1); set phi2 = radians(lat2); set d_phi = radians(lat2-lat1); set d_lambda = radians(lon2-lon1); set a = sin(d_phi/2) * sin(d_phi/2) + cos(phi1) * cos(phi2) * sin(d_lambda/2) * sin(d_lambda/2); set c = 2 * atan2(sqrt(a), sqrt(1-a)); set d = R * c; return d; end;//delimiter ;
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(the algorithm is based on the standard formula, I’ve used the well-known Movable Type scripts calculator )

This is a slower implementation as it uses arctangent , however it is more precise. 

MySQL UDF for Haversine distance

Another approach, which will give you much more performance is to use UDF. There are a number of implementations, I’ve used lib_mysqludf_haversine .

Here is the simple steps to install it in MySQL 5.6 (will also work with earlier versions):

$ wget 'https://github.com/lucasepe/lib_mysqludf_haversine/archive/master.zip'$ unzip master.zip$ cd lib_mysqludf_haversine-master/$ makemysql> show global variables like 'plugin%';+---------------+-------------------------+| Variable_name | Value |+---------------+-------------------------+| plugin_dir| /usr/lib64/mysql/plugin |+---------------+-------------------------+1 row in set (0.00 sec)$ sudo cp lib_mysqludf_haversine.so /usr/lib64/mysql/plugin/mysql> CREATE FUNCTION haversine_distance RETURNS REAL SONAME 'lib_mysqludf_haversine.so';mysql> select haversine_distance(37.470295464, -122.572938858498, 37.760150536, -122.20701914150199, 'mi') as dist_in_miles;+---------------+| dist_in_miles |+---------------+| 28.330467 |+---------------+1 row in set (0.00 sec)
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Please note:

  • Make sure you have the mysql-devel or percona-server-devel package installed (MySQL development libraries) before installing.
  • You will need to specify the last parameter to be “mi” if you want to get the results in miles, otherwise it will give you kilometers.

MySQL ST_distance function

In MySQL 5.6 you can use ST_distance function:

mysql> select st_distance(point(37.470295464, -122.572938858498), point( 37.760150536, -122.20701914150199)) as distance_plane;+---------------------+| distance_plane|+---------------------+| 0.46681174155173943 |+---------------------+1 row in set (0.00 sec)
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As we can see it does not give us an actual distance in mile or kilometers as it does not take into account that we have latitude and longitude, rather than X and Y on plane.

Geo Distance Functions Performance

The stored procedures and functions in MySQL are known to be slower, especially with trigonometrical functions. I’ve did a quick test, using MySQL function benchmark .

First I set 2 points (10 miles from SFO airport)

set @rlon1 = 122.572938858498;set @rlat1 = 37.470295464;set @rlon2 = -122.20701914150199;set @rlat2 = 37.760150536;
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Next I use 4 function to benchmark:

  • Less precise stored function (haversine)
  • More precise stored function (haversine)
  • UDF for haversine
  • MySQL 5.6 native ST_distance (plane)

The benchmark function will execute the above function 100000 times.

Here are the results:

mysql>select benchmark(100000,haversine_old_sp(@rlat1, @rlon1, @rlat2, @rlon2)) as less_precise_mysql_stored_proc;+--------------------------------+| less_precise_mysql_stored_proc |+--------------------------------+|0 |+--------------------------------+1 row in set (1.46 sec)mysql>select benchmark(100000,haversine_distance_sp(@rlat1, @rlon1, @rlat2, @rlon2)) as more_precise_mysql_stored_proc;+--------------------------------+| more_precise_mysql_stored_proc |+--------------------------------+|0 |+--------------------------------+1 row in set (2.58 sec)mysql>select benchmark(100000,haversine_distance(@rlat1, @rlon1, @rlat2, @rlon2, 'mi')) as udf_haversine_function;+------------------------+| udf_haversine_function |+------------------------+|0 |+------------------------+1 row in set (0.17 sec)mysql> select benchmark(100000, st_distance(point(@rlat1, @rlon1), point(@rlat2, @rlon1))) as mysql_builtin_st_distance;+---------------------------+| mysql_builtin_st_distance |+---------------------------+| 0 |+---------------------------+1 row in set (0.10 sec)
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As we can see the UDF gives much faster response time (which is comparable to built-in function).

Benchmark chart (smaller the better)

Using UDFs for Geo-Distance Search in MySQL_MySQL Conclusion

The lib_mysqludf_haversine  UDF provides a good function for geo-distance search in MySQL. Please let me know in the comments what geo-distance functions or approaches do you use in your applications.

Published at DZone with permission ofPeter Zaitsev, author and DZone MVB. ( source )

(Note: Opinions expressed in this article and its replies are the opinions of their respective authors and not those of DZone, Inc.)

Tags:
  • geo-distance search
  • MySQL
  • Tips and Tricks
  • SQL
  • Tools & Methods
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