I’m trying to write a recursive stored procedure or function to auto-generate large amount of hierarchical (tree) data for dissertation experiment.

What I find out is that, in MySQL, only recursive stored procedure is allowed, where stored function is not allowed. So, the following procedure works:

delimiter //
create procedure rec_seq(min int, max int, result text)
	-- Put current value into result
	set result = concat(result, min);
	if min != max then
		set result = concat(result, ' ');
	end if;
	if min = max then
		-- Output result
		select result;
		-- Recursive call
		call rec_seq(min + 1, max, result);
	end if;
delimiter ;

Where as the following very similar stored function will not run:

delimiter //

create function rec_seq(min int, max int) RETURNS text CHARSET latin1
	if min = max then
		return min;
	end if;

	set @result = '';
	set @result = concat(@result, min);
	set @result = concat(@result, ',');
	set @result = concat(@result, rec_seq(min + 1, max));
	return @result;

To run the stored procedure, we need to increase the max_sp_recursion_depth, which is set to 0 on my installation. To run the procedure, I execute the following:

set max_sp_recursion_depth = 200;
call rec_seq(1,10, '');

This produce the following output:

mysql> call rec_seq(1,10,'');
| result               |
| 1 2 3 4 5 6 7 8 9 10 |
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

When I run the stored procedure with range from 1 to 15, even with this simple script I get a stack overflow error:

mysql> call rec_seq(1,12,'');
ERROR 1436 (HY000): Thread stack overrun:  70208 bytes used of a 196608 byte stack, and 128000 bytes needed.  Use 'mysqld --thread_stack=#' to specify a bigger stack.

My solution was to edit /etc/mysql/my.cnf and change thread_stack from 192k to a higher value. The following is my change:

# * Fine Tuning
key_buffer              = 16M
max_allowed_packet      = 16M
**thread_stack            = 512K**
thread_cache_size       = 8
# This replaces the startup script and checks MyISAM tables if needed
# the first time they are touched