MySQL Bugs: #33: RAND() not seeded upon thread creation

Bug #33	RAND() not seeded upon thread creation
Submitted:	16 Jan 2003 15:18	Modified:	28 Jan 2003 16:46
Reporter:	Alexander Keremidarski	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server	Severity:	S3 (Non-critical)
Version:	4.0	OS:
Assigned to:		CPU Architecture:	Any

Description:
When first called RAND() returns 'predictable' results.

Impact is huge as it means simultaneous connections (even close in terms of time) get same value up to 2 digits after floating point.

In real world worst case is with:

SELECT ... ORDRER BY RAND() LIMIT 1;

"Random" row acrually is fixed - from 100 simultaneous web recuests for example 99 will get SAME row. Quite bad for Banners rotating systems.

How to repeat:
# while true; do mysql -B -N -u root -e "select @r:=rand(), round(@r,2)"; done

Observe the result. Depending on system clock it will be something like:

0.40013473797602        0.40
0.40938241166005        0.41
0.40776392762341        0.41
0.40366006400777        0.40
0.40051618907649        0.40
0.40239181127622        0.40
0.40593299959407        0.41
0.40348305218246        0.40
0.40552761629739        0.41

Suggested fix:
Currently RAND() depends on randominit() which is declared in mysys/my_password.c

Writing my_rand.c should be better i.e. moving it out of auth code.

Sorry, but the bug system is not the appropriate forum for asking
support questions. Your problem is not the result of a bug.
For a list of more appropriate places to ask for help using MySQL
products, please visit http://www.mysql.com/support/

Thank you for your interest in MySQL.

Not a bug, only not optimal behaviour.
To be fixed in 4.1