Bug #80101 potential contention when releasing transaction locks.
Submitted: 21 Jan 2016 17:53 Modified: 28 Jun 2018 15:03
Reporter: Tingting Yu Email Updates:
Status: Not a Bug Impact on me:
None 
Category:MySQL Server Severity:S5 (Performance)
Version:5.7.10 OS:Ubuntu (14.04)
Assigned to: CPU Architecture:Any

[21 Jan 2016 17:53] Tingting Yu 
Description:
When using a read-only transaction (e.g, Select-From-Where query), lock_mutex_enter()  caused the most thread time. When examining the lock_trx_release_locks() in storage/innobase/lock/lock0lock.cc, it seems that 
the lock_mutex_enter() does not need to be acquired for transactions that do not change states. 

How to repeat:
Run Select-From-Where query with large workloads. 

Suggested fix:
Check whether a transaction is read-only, and returns without acquiring lock_mutex_enter().
[22 Jan 2016 1:17] zhai weixiang 
ref bug#76728 which is still open
[28 Jun 2018 15:03] MySQL Verification Team 
Hi,

Thank you for your performance bug report.

However, this seems to be fixed already. Bug #76728 is not open. It is fully fixed and closed. If you read the last comment, you will notice that you are using an outdated release of our 5.7 version.