Bug #87402 Redundant check in ut_rnd_gen_ulint()
Submitted: 11 Aug 2017 15:59 Modified: 14 Aug 2017 9:58
Reporter: Alexey Kopytov Email Updates:
Status: Verified Impact on me:
Category:MySQL Server: InnoDB storage engine Severity:S5 (Performance)
Version:8.0.2 OS:Any
Assigned to: CPU Architecture:Any

[11 Aug 2017 15:59] Alexey Kopytov
In 8.0.2 my_thread_local* variables have been replaced with C++11
thread-local storage. One piece of code which is now redundant due to
that change is the following part of ut_rnd_gen_ulint():

	ulint	rnd = ut_rnd_ulint_counter;
	if (rnd == 0) {
		rnd = 65654363;

The check above was only required because the combination of
my_thread_local_key, my_set_thread_local() and my_get_thread_local()
essentially emulated thread-local storage and did not allow automatic
initialization of thread-local variables.

That check on a critical code path can be avoided if
ut_rnd_ulint_counter is initialized to 65654363 rather than zero in

How to repeat:
Code analysis of ut_rnd_gen_ulint() and ut_rnd_ulint_counter

Suggested fix:
See above.
[14 Aug 2017 9:58] MySQL Verification Team
Hello Alexey,

Thank you for your feedback!
Verifying based on my internal discussion with developer.